chore: update maintainer list: Junjie Gao retired (#282)

Signed-off-by: Junjie Gao <junjiegao@microsoft.com>

.github/.codecov.yml

@@ -16,3 +16,6 @@ coverage:
     project:
       default:
         target: 89%
+    patch:
+      default:
+        target: 90%

.github/workflows/build.yml

@@ -22,3 +22,5 @@ on:
 jobs:
   build:
     uses: ./.github/workflows/reusable-build.yml
+    secrets:
+      CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}

.github/workflows/reusable-build.yml

@@ -15,23 +15,28 @@ name: Reusable build
 
 on:
   workflow_call:
+    secrets:
+      CODECOV_TOKEN:
+        required: true
 
 jobs:
   build:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go-version: ["1.20", "1.21"]
+        go-version: ["1.23", "1.24"]
       fail-fast: true
     steps:
       - name: Checkout
         uses: actions/checkout@v4
       - name: Set up Go ${{ matrix.go-version }} environment
-        uses: actions/setup-go@v4
+        uses: actions/setup-go@v5
         with:
           go-version: ${{ matrix.go-version }}
           check-latest: true
       - name: Run unit tests
         run: make test
       - name: Upload coverage to codecov.io
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v5
+        env:
+          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}

.github/workflows/reusable-codeql.yml

@@ -26,19 +26,19 @@ jobs:
       security-events: write
     strategy:
       matrix:
-        go-version: ["1.20", "1.21"]
+        go-version: ["1.23", "1.24"]
       fail-fast: false
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
       - name: Set up Go ${{ matrix.go-version }} environment
-        uses: actions/setup-go@v4
+        uses: actions/setup-go@v5
         with:
           go-version: ${{ matrix.go-version }}
           check-latest: true
       - name: Initialize CodeQL
-        uses: github/codeql-action/init@v2
+        uses: github/codeql-action/init@v3
         with:
           languages: go
       - name: Perform CodeQL Analysis
-        uses: github/codeql-action/analyze@v2
+        uses: github/codeql-action/analyze@v3

.github/workflows/reusable-license-checker.yml

@@ -23,11 +23,14 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
       - name: Check license header
-        uses: apache/skywalking-eyes/header@v0.4.0
+        uses: apache/skywalking-eyes/header@5c5b974209f0de5d905f37deb69369068ebfc15c
+
         with:
           mode: check
           config: .github/licenserc.yml
       - name: Check dependencies license
-        uses: apache/skywalking-eyes/dependency@v0.4.0
+        uses: apache/skywalking-eyes/dependency@5c5b974209f0de5d905f37deb69369068ebfc15c
         with:
           config: .github/licenserc.yml
+          flags:
+            --weak-compatible=true

.github/workflows/stale.yml

@@ -0,0 +1,33 @@
+# Copyright The Notary Project Authors.
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+name: "Close stale issues and PRs"
+on:
+  schedule:
+    - cron: "30 1 * * *"
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/stale@v9
+        with:
+          stale-issue-message: "This issue is stale because it has been opened for 60 days with no activity. Remove stale label or comment. Otherwise, it will be closed in 30 days."
+          stale-pr-message: "This PR is stale because it has been opened for 45 days with no activity. Remove stale label or comment. Otherwise, it will be closed in 30 days."
+          close-issue-message: "Issue closed due to no activity in the past 30 days."
+          close-pr-message: "PR closed due to no activity in the past 30 days."
+          days-before-issue-stale: 60
+          days-before-pr-stale: 45
+          days-before-issue-close: 30
+          days-before-pr-close: 30
+          exempt-all-milestones: true

CODEOWNERS

@@ -1,3 +1,3 @@
 # Repo-Level Owners (in alphabetical order)
 # Note: This is only for the notaryproject/notation-core-go repo
-* @gokarnm @JeyJeyGao @justincormack @niazfk @priteshbandi @rgnote @shizhMSFT @stevelasker @Two-Hearts
+* @gokarnm @niazfk @priteshbandi @rgnote @shizhMSFT @toddysm @Two-Hearts @vaninrao10 @yizha1

MAINTAINERS

@@ -1,14 +1,22 @@
 # Org-Level Maintainers (in alphabetical order)
 # Pattern: [First Name] [Last Name] <[Email Address]> ([GitHub Handle])
-Justin Cormack <justin.cormack@docker.com> (@justincormack)
 Niaz Khan <niazfk@amazon.com> (@niazfk)
-Steve Lasker <StevenLasker@hotmail.com> (@stevelasker)
+Pritesh Bandi <priteshbandi@gmail.com> (@priteshbandi)
+Shiwei Zhang <shizh@microsoft.com> (@shizhMSFT)
+Toddy Mladenov <toddysm@gmail.com> (@toddysm)
+Vani Rao <vaninrao@amazon.com> (@vaninrao10)
+Yi Zha <yizha1@microsoft.com> (@yizha1)
+
 
 # Repo-Level Maintainers (in alphabetical order)
 # Note: This is for the notaryproject/notation-core-go repo
-Junjie Gao <junjiegao@microsoft.com> (@JeyJeyGao)
 Milind Gokarn <gokarnm@amazon.com> (@gokarnm)
 Patrick Zheng <patrickzheng@microsoft.com> (@Two-Hearts)
-Pritesh Bandi <priteshbandi@gmail.com> (@priteshbandi)
 Rakesh Gariganti <garigant@amazon.com> (@rgnote)
-Shiwei Zhang <shizh@microsoft.com> (@shizhMSFT)
+
+# Emeritus Org Maintainers (in alphabetical order)
+Justin Cormack <justin.cormack@docker.com> (@justincormack)
+Steve Lasker <StevenLasker@hotmail.com> (@stevelasker)
+
+# Emeritus Repo-Level Maintainers (in alphabetical order)
+Junjie Gao <junjiegao@microsoft.com> (@JeyJeyGao)

Makefile

@@ -29,7 +29,7 @@ clean:
 .PHONY: check-line-endings
 check-line-endings: ## check line endings
 	! find . -name "*.go" -type f -exec file "{}" ";" | grep CRLF
-	! find scripts -name "*.sh" -type f -exec file "{}" ";" | grep CRLF
+	! find . -name "*.sh" -type f -exec file "{}" ";" | grep CRLF
 
 .PHONY: fix-line-endings
 fix-line-endings: ## fix line endings

README.md

@@ -4,4 +4,28 @@
 [![codecov](https://codecov.io/gh/notaryproject/notation-core-go/branch/main/graph/badge.svg)](https://codecov.io/gh/notaryproject/notation-core-go)
 [![Go Reference](https://pkg.go.dev/badge/github.com/notaryproject/notation-core-go.svg)](https://pkg.go.dev/github.com/notaryproject/notation-core-go@main)
 
-Contains support for Notary Project signature envelope, and format specific implementation
+notation-core-go provides core crypto functionality for notation-go and implements signature generation, parsing and revocation related functionalities based on the [Notary Project specifications](https://github.com/notaryproject/specifications). It also provides validation functionality for certificate and certificate chain.
+
+notation-core-go reached a stable release as of July 2023 and continues to be actively developed and maintained.
+
+Please visit [README](https://github.com/notaryproject/.github/blob/main/README.md) to know more about Notary Project.
+
+> [!NOTE]
+> The Notary Project documentation is available [here](https://notaryproject.dev/docs/).
+
+## Table of Contents
+- [Documentation](#documentation)
+- [Code of Conduct](#code-of-conduct)
+- [License](#license)
+ 
+## Documentation
+
+Library documentation is available at [Go Reference](https://pkg.go.dev/github.com/notaryproject/notation-core-go).
+
+## Code of Conduct
+
+This project has adopted the [CNCF Code of Conduct](https://github.com/cncf/foundation/blob/master/code-of-conduct.md). See [CODE_OF_CONDUCT.md](CODE_OF_CONDUCT.md) for further details.
+
+## License
+
+This project is covered under the Apache 2.0 license. You can read the license [here](LICENSE).

go.mod

@@ -1,12 +1,13 @@
 module github.com/notaryproject/notation-core-go
 
-go 1.20
+go 1.23.0
 
 require (
-	github.com/fxamacker/cbor/v2 v2.5.0
+	github.com/fxamacker/cbor/v2 v2.8.0
-	github.com/golang-jwt/jwt/v4 v4.5.0
+	github.com/golang-jwt/jwt/v4 v4.5.2
-	github.com/veraison/go-cose v1.1.0
+	github.com/notaryproject/tspclient-go v1.0.0
-	golang.org/x/crypto v0.14.0
+	github.com/veraison/go-cose v1.3.0
+	golang.org/x/crypto v0.37.0
 )
 
 require github.com/x448/float16 v0.8.4 // indirect

go.sum

@@ -1,10 +1,12 @@
-github.com/fxamacker/cbor/v2 v2.5.0 h1:oHsG0V/Q6E/wqTS2O1Cozzsy69nqCiguo5Q1a1ADivE=
+github.com/fxamacker/cbor/v2 v2.8.0 h1:fFtUGXUzXPHTIUdne5+zzMPTfffl3RD5qYnkY40vtxU=
-github.com/fxamacker/cbor/v2 v2.5.0/go.mod h1:TA1xS00nchWmaBnEIxPSE5oHLuJBAVvqrtAnWBwBCVo=
+github.com/fxamacker/cbor/v2 v2.8.0/go.mod h1:vM4b+DJCtHn+zz7h3FFp/hDAI9WNWCsZj23V5ytsSxQ=
-github.com/golang-jwt/jwt/v4 v4.5.0 h1:7cYmW1XlMY7h7ii7UhUyChSgS5wUJEnm9uZVTGqOWzg=
+github.com/golang-jwt/jwt/v4 v4.5.2 h1:YtQM7lnr8iZ+j5q71MGKkNw9Mn7AjHM68uc9g5fXeUI=
-github.com/golang-jwt/jwt/v4 v4.5.0/go.mod h1:m21LjoU+eqJr34lmDMbreY2eSTRJ1cv77w39/MY0Ch0=
+github.com/golang-jwt/jwt/v4 v4.5.2/go.mod h1:m21LjoU+eqJr34lmDMbreY2eSTRJ1cv77w39/MY0Ch0=
-github.com/veraison/go-cose v1.1.0 h1:AalPS4VGiKavpAzIlBjrn7bhqXiXi4jbMYY/2+UC+4o=
+github.com/notaryproject/tspclient-go v1.0.0 h1:AwQ4x0gX8IHnyiZB1tggpn5NFqHpTEm1SDX8YNv4Dg4=
-github.com/veraison/go-cose v1.1.0/go.mod h1:7ziE85vSq4ScFTg6wyoMXjucIGOf4JkFEZi/an96Ct4=
+github.com/notaryproject/tspclient-go v1.0.0/go.mod h1:LGyA/6Kwd2FlM0uk8Vc5il3j0CddbWSHBj/4kxQDbjs=
+github.com/veraison/go-cose v1.3.0 h1:2/H5w8kdSpQJyVtIhx8gmwPJ2uSz1PkyWFx0idbd7rk=
+github.com/veraison/go-cose v1.3.0/go.mod h1:df09OV91aHoQWLmy1KsDdYiagtXgyAwAl8vFeFn1gMc=
 github.com/x448/float16 v0.8.4 h1:qLwI1I70+NjRFUR3zs1JPUCgaCXSh3SW62uAKT1mSBM=
 github.com/x448/float16 v0.8.4/go.mod h1:14CWIYCyZA/cWjXOioeEpHeN/83MdbZDRQHoFcYsOfg=
-golang.org/x/crypto v0.14.0 h1:wBqGXzWJW6m1XrIKlAH0Hs1JJ7+9KBwnIO8v66Q9cHc=
+golang.org/x/crypto v0.37.0 h1:kJNSjF/Xp7kU0iB2Z+9viTPMW4EqqsrywMXLJOOsXSE=
-golang.org/x/crypto v0.14.0/go.mod h1:MVFd36DqK4CsrnJYDkBA3VC4m2GkXAM0PvzMCn4JQf4=
+golang.org/x/crypto v0.37.0/go.mod h1:vg+k43peMZ0pUMhYmVAWysMK35e6ioLh3wB8ZCAfbVc=

internal/algorithm/algorithm.go

@@ -0,0 +1,121 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package algorithm includes signature algorithms accepted by Notary Project
+package algorithm
+
+import (
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/rsa"
+	"crypto/x509"
+	"errors"
+	"fmt"
+)
+
+// Algorithm defines the signature algorithm.
+type Algorithm int
+
+// Signature algorithms supported by this library.
+//
+// Reference: https://github.com/notaryproject/notaryproject/blob/main/specs/signature-specification.md#algorithm-selection
+const (
+	AlgorithmPS256 Algorithm = 1 + iota // RSASSA-PSS with SHA-256
+	AlgorithmPS384                      // RSASSA-PSS with SHA-384
+	AlgorithmPS512                      // RSASSA-PSS with SHA-512
+	AlgorithmES256                      // ECDSA on secp256r1 with SHA-256
+	AlgorithmES384                      // ECDSA on secp384r1 with SHA-384
+	AlgorithmES512                      // ECDSA on secp521r1 with SHA-512
+)
+
+// Hash returns the hash function of the algorithm.
+func (alg Algorithm) Hash() crypto.Hash {
+	switch alg {
+	case AlgorithmPS256, AlgorithmES256:
+		return crypto.SHA256
+	case AlgorithmPS384, AlgorithmES384:
+		return crypto.SHA384
+	case AlgorithmPS512, AlgorithmES512:
+		return crypto.SHA512
+	}
+	return 0
+}
+
+// KeyType defines the key type.
+type KeyType int
+
+const (
+	KeyTypeRSA KeyType = 1 + iota // KeyType RSA
+	KeyTypeEC                     // KeyType EC
+)
+
+// KeySpec defines a key type and size.
+type KeySpec struct {
+	// KeyType is the type of the key.
+	Type KeyType
+
+	// KeySize is the size of the key in bits.
+	Size int
+}
+
+// SignatureAlgorithm returns the signing algorithm associated with the KeySpec.
+func (k KeySpec) SignatureAlgorithm() Algorithm {
+	switch k.Type {
+	case KeyTypeEC:
+		switch k.Size {
+		case 256:
+			return AlgorithmES256
+		case 384:
+			return AlgorithmES384
+		case 521:
+			return AlgorithmES512
+		}
+	case KeyTypeRSA:
+		switch k.Size {
+		case 2048:
+			return AlgorithmPS256
+		case 3072:
+			return AlgorithmPS384
+		case 4096:
+			return AlgorithmPS512
+		}
+	}
+	return 0
+}
+
+// ExtractKeySpec extracts KeySpec from the signing certificate.
+func ExtractKeySpec(signingCert *x509.Certificate) (KeySpec, error) {
+	switch key := signingCert.PublicKey.(type) {
+	case *rsa.PublicKey:
+		switch bitSize := key.Size() << 3; bitSize {
+		case 2048, 3072, 4096:
+			return KeySpec{
+				Type: KeyTypeRSA,
+				Size: bitSize,
+			}, nil
+		default:
+			return KeySpec{}, fmt.Errorf("rsa key size %d bits is not supported", bitSize)
+		}
+	case *ecdsa.PublicKey:
+		switch bitSize := key.Curve.Params().BitSize; bitSize {
+		case 256, 384, 521:
+			return KeySpec{
+				Type: KeyTypeEC,
+				Size: bitSize,
+			}, nil
+		default:
+			return KeySpec{}, fmt.Errorf("ecdsa key size %d bits is not supported", bitSize)
+		}
+	}
+	return KeySpec{}, errors.New("unsupported public key type")
+}

internal/algorithm/algorithm_test.go

@@ -0,0 +1,244 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package algorithm
+
+import (
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/ed25519"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/x509"
+	"reflect"
+	"strconv"
+	"testing"
+
+	"github.com/notaryproject/notation-core-go/testhelper"
+)
+
+func TestHash(t *testing.T) {
+	tests := []struct {
+		name   string
+		alg    Algorithm
+		expect crypto.Hash
+	}{
+		{
+			name:   "PS256",
+			alg:    AlgorithmPS256,
+			expect: crypto.SHA256,
+		},
+		{
+			name:   "ES256",
+			alg:    AlgorithmES256,
+			expect: crypto.SHA256,
+		},
+		{
+			name:   "PS384",
+			alg:    AlgorithmPS384,
+			expect: crypto.SHA384,
+		},
+		{
+			name:   "ES384",
+			alg:    AlgorithmES384,
+			expect: crypto.SHA384,
+		},
+		{
+			name:   "PS512",
+			alg:    AlgorithmPS512,
+			expect: crypto.SHA512,
+		},
+		{
+			name:   "ES512",
+			alg:    AlgorithmES512,
+			expect: crypto.SHA512,
+		},
+		{
+			name:   "UnsupportedAlgorithm",
+			alg:    0,
+			expect: 0,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			hash := tt.alg.Hash()
+			if hash != tt.expect {
+				t.Fatalf("Expected %v, got %v", tt.expect, hash)
+			}
+		})
+	}
+}
+
+func TestSignatureAlgorithm(t *testing.T) {
+	tests := []struct {
+		name    string
+		keySpec KeySpec
+		expect  Algorithm
+	}{
+		{
+			name: "EC 256",
+			keySpec: KeySpec{
+				Type: KeyTypeEC,
+				Size: 256,
+			},
+			expect: AlgorithmES256,
+		},
+		{
+			name: "EC 384",
+			keySpec: KeySpec{
+				Type: KeyTypeEC,
+				Size: 384,
+			},
+			expect: AlgorithmES384,
+		},
+		{
+			name: "EC 521",
+			keySpec: KeySpec{
+				Type: KeyTypeEC,
+				Size: 521,
+			},
+			expect: AlgorithmES512,
+		},
+		{
+			name: "RSA 2048",
+			keySpec: KeySpec{
+				Type: KeyTypeRSA,
+				Size: 2048,
+			},
+			expect: AlgorithmPS256,
+		},
+		{
+			name: "RSA 3072",
+			keySpec: KeySpec{
+				Type: KeyTypeRSA,
+				Size: 3072,
+			},
+			expect: AlgorithmPS384,
+		},
+		{
+			name: "RSA 4096",
+			keySpec: KeySpec{
+				Type: KeyTypeRSA,
+				Size: 4096,
+			},
+			expect: AlgorithmPS512,
+		},
+		{
+			name: "Unsupported key spec",
+			keySpec: KeySpec{
+				Type: 0,
+				Size: 0,
+			},
+			expect: 0,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			alg := tt.keySpec.SignatureAlgorithm()
+			if alg != tt.expect {
+				t.Errorf("unexpected signature algorithm: %v, expect: %v", alg, tt.expect)
+			}
+		})
+	}
+}
+
+func TestExtractKeySpec(t *testing.T) {
+	type testCase struct {
+		name      string
+		cert      *x509.Certificate
+		expect    KeySpec
+		expectErr bool
+	}
+	// invalid cases
+	tests := []testCase{
+		{
+			name:      "RSA wrong size",
+			cert:      testhelper.GetUnsupportedRSACert().Cert,
+			expect:    KeySpec{},
+			expectErr: true,
+		},
+		{
+			name:      "ECDSA wrong size",
+			cert:      testhelper.GetUnsupportedECCert().Cert,
+			expect:    KeySpec{},
+			expectErr: true,
+		},
+		{
+			name: "Unsupported type",
+			cert: &x509.Certificate{
+				PublicKey: ed25519.PublicKey{},
+			},
+			expect:    KeySpec{},
+			expectErr: true,
+		},
+	}
+
+	// append valid RSA cases
+	for _, k := range []int{2048, 3072, 4096} {
+		rsaRoot := testhelper.GetRSARootCertificate()
+		priv, _ := rsa.GenerateKey(rand.Reader, k)
+
+		certTuple := testhelper.GetRSACertTupleWithPK(
+			priv,
+			"Test RSA_"+strconv.Itoa(priv.Size()),
+			&rsaRoot,
+		)
+		tests = append(tests, testCase{
+			name: "RSA " + strconv.Itoa(k),
+			cert: certTuple.Cert,
+			expect: KeySpec{
+				Type: KeyTypeRSA,
+				Size: k,
+			},
+			expectErr: false,
+		})
+	}
+
+	// append valid EDCSA cases
+	for _, curve := range []elliptic.Curve{elliptic.P256(), elliptic.P384(), elliptic.P521()} {
+		ecdsaRoot := testhelper.GetECRootCertificate()
+		priv, _ := ecdsa.GenerateKey(curve, rand.Reader)
+		bitSize := priv.Params().BitSize
+
+		certTuple := testhelper.GetECDSACertTupleWithPK(
+			priv,
+			"Test EC_"+strconv.Itoa(bitSize),
+			&ecdsaRoot,
+		)
+		tests = append(tests, testCase{
+			name: "EC " + strconv.Itoa(bitSize),
+			cert: certTuple.Cert,
+			expect: KeySpec{
+				Type: KeyTypeEC,
+				Size: bitSize,
+			},
+			expectErr: false,
+		})
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			keySpec, err := ExtractKeySpec(tt.cert)
+
+			if (err != nil) != tt.expectErr {
+				t.Errorf("error = %v, expectErr = %v", err, tt.expectErr)
+			}
+			if !reflect.DeepEqual(keySpec, tt.expect) {
+				t.Errorf("expect %+v, got %+v", tt.expect, keySpec)
+			}
+		})
+	}
+}

internal/oid/oid.go

@@ -0,0 +1,31 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package oid
+
+import "encoding/asn1"
+
+// KeyUsage (id-ce-keyUsage) is defined in RFC 5280
+//
+// Reference: https://www.rfc-editor.org/rfc/rfc5280.html#section-4.2.1.3
+var KeyUsage = asn1.ObjectIdentifier{2, 5, 29, 15}
+
+// ExtKeyUsage (id-ce-extKeyUsage) is defined in RFC 5280
+//
+// Reference: https://www.rfc-editor.org/rfc/rfc5280.html#section-4.2.1.12
+var ExtKeyUsage = asn1.ObjectIdentifier{2, 5, 29, 37}
+
+// Timestamping (id-kp-timeStamping) is defined in RFC 3161 2.3
+//
+// Reference: https://datatracker.ietf.org/doc/html/rfc3161#section-2.3
+var Timestamping = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 8}

internal/timestamp/timestamp.go

@@ -0,0 +1,109 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package timestamp provides functionalities of timestamp countersignature
+package timestamp
+
+import (
+	"crypto/x509"
+	"errors"
+	"fmt"
+
+	"github.com/notaryproject/notation-core-go/revocation"
+	"github.com/notaryproject/notation-core-go/revocation/result"
+	"github.com/notaryproject/notation-core-go/signature"
+	nx509 "github.com/notaryproject/notation-core-go/x509"
+	"github.com/notaryproject/tspclient-go"
+)
+
+// Timestamp generates a timestamp request and sends to TSA. It then validates
+// the TSA certificate chain against Notary Project certificate and signature
+// algorithm requirements.
+// On success, it returns the full bytes of the timestamp token received from
+// TSA.
+//
+// Reference: https://github.com/notaryproject/specifications/blob/v1.0.0/specs/signature-specification.md#leaf-certificates
+func Timestamp(req *signature.SignRequest, opts tspclient.RequestOptions) ([]byte, error) {
+	tsaRequest, err := tspclient.NewRequest(opts)
+	if err != nil {
+		return nil, err
+	}
+	ctx := req.Context()
+	resp, err := req.Timestamper.Timestamp(ctx, tsaRequest)
+	if err != nil {
+		return nil, err
+	}
+	token, err := resp.SignedToken()
+	if err != nil {
+		return nil, err
+	}
+	tsaCertChain, err := token.Verify(ctx, x509.VerifyOptions{
+		Roots: req.TSARootCAs,
+	})
+	if err != nil {
+		return nil, err
+	}
+	if err := nx509.ValidateTimestampingCertChain(tsaCertChain); err != nil {
+		return nil, err
+	}
+	// certificate chain revocation check after timestamping
+	if req.TSARevocationValidator != nil {
+		certResults, err := req.TSARevocationValidator.ValidateContext(ctx, revocation.ValidateContextOptions{
+			CertChain: tsaCertChain,
+		})
+		if err != nil {
+			return nil, fmt.Errorf("failed to validate the revocation status of timestamping certificate chain with error: %w", err)
+		}
+		if err := revocationResult(certResults, tsaCertChain); err != nil {
+			return nil, err
+		}
+	}
+	return resp.TimestampToken.FullBytes, nil
+}
+
+// revocationResult returns an error if any cert in the cert chain has
+// a revocation status other than ResultOK or ResultNonRevokable.
+// When ResultRevoked presents, always return the revoked error.
+func revocationResult(certResults []*result.CertRevocationResult, certChain []*x509.Certificate) error {
+	//sanity check
+	if len(certResults) == 0 {
+		return errors.New("certificate revocation result cannot be empty")
+	}
+	if len(certResults) != len(certChain) {
+		return fmt.Errorf("length of certificate revocation result %d does not match length of the certificate chain %d", len(certResults), len(certChain))
+	}
+
+	numOKResults := 0
+	var problematicCertSubject string
+	var hasUnknownResult bool
+	for i := len(certResults) - 1; i >= 0; i-- {
+		cert := certChain[i]
+		certResult := certResults[i]
+		if certResult.Result == result.ResultOK || certResult.Result == result.ResultNonRevokable {
+			numOKResults++
+		} else {
+			if certResult.Result == result.ResultRevoked { // revoked
+				return fmt.Errorf("timestamping certificate with subject %q is revoked", cert.Subject.String())
+			}
+			if !hasUnknownResult { // unknown
+				// not returning because a following cert can be revoked
+				problematicCertSubject = cert.Subject.String()
+				hasUnknownResult = true
+			}
+		}
+	}
+	if numOKResults != len(certResults) {
+		return fmt.Errorf("timestamping certificate with subject %q revocation status is unknown", problematicCertSubject)
+	}
+	return nil
+}

internal/timestamp/timestamp_test.go

@@ -0,0 +1,383 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package timestamp
+
+import (
+	"context"
+	"crypto"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/asn1"
+	"errors"
+	"os"
+	"strings"
+	"testing"
+
+	"github.com/notaryproject/notation-core-go/revocation"
+	"github.com/notaryproject/notation-core-go/revocation/result"
+	"github.com/notaryproject/notation-core-go/signature"
+	nx509 "github.com/notaryproject/notation-core-go/x509"
+	"github.com/notaryproject/tspclient-go"
+	"github.com/notaryproject/tspclient-go/pki"
+)
+
+const rfc3161TSAurl = "http://timestamp.digicert.com"
+
+func TestTimestamp(t *testing.T) {
+	rootCerts, err := nx509.ReadCertificateFile("testdata/tsaRootCert.cer")
+	if err != nil || len(rootCerts) == 0 {
+		t.Fatal("failed to read root CA certificate:", err)
+	}
+	rootCert := rootCerts[0]
+	rootCAs := x509.NewCertPool()
+	rootCAs.AddCert(rootCert)
+
+	// --------------- Success case ----------------------------------
+	t.Run("Timestamping success", func(t *testing.T) {
+		timestamper, err := tspclient.NewHTTPTimestamper(nil, rfc3161TSAurl)
+		if err != nil {
+			t.Fatal(err)
+		}
+		req := &signature.SignRequest{
+			Timestamper: timestamper,
+			TSARootCAs:  rootCAs,
+		}
+		opts := tspclient.RequestOptions{
+			Content:       []byte("notation"),
+			HashAlgorithm: crypto.SHA256,
+		}
+		_, err = Timestamp(req, opts)
+		if err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	// ------------- Failure cases ------------------------
+	t.Run("Timestamping SHA-1", func(t *testing.T) {
+		timestamper, err := tspclient.NewHTTPTimestamper(nil, rfc3161TSAurl)
+		if err != nil {
+			t.Fatal(err)
+		}
+		req := &signature.SignRequest{
+			Timestamper: timestamper,
+			TSARootCAs:  rootCAs,
+		}
+		opts := tspclient.RequestOptions{
+			Content:       []byte("notation"),
+			HashAlgorithm: crypto.SHA1,
+		}
+		expectedErr := "malformed timestamping request: unsupported hashing algorithm: SHA-1"
+		_, err = Timestamp(req, opts)
+		assertErrorEqual(expectedErr, err, t)
+	})
+
+	t.Run("Timestamping failed", func(t *testing.T) {
+		req := &signature.SignRequest{
+			Timestamper: dummyTimestamper{},
+			TSARootCAs:  rootCAs,
+		}
+		opts := tspclient.RequestOptions{
+			Content:       []byte("notation"),
+			HashAlgorithm: crypto.SHA256,
+		}
+		expectedErr := "failed to timestamp"
+		_, err = Timestamp(req, opts)
+		if err == nil || !strings.Contains(err.Error(), expectedErr) {
+			t.Fatalf("expected error message to contain %s, but got %v", expectedErr, err)
+		}
+	})
+
+	t.Run("Timestamping rejected", func(t *testing.T) {
+		req := &signature.SignRequest{
+			Timestamper: dummyTimestamper{
+				respWithRejectedStatus: true,
+			},
+			TSARootCAs: rootCAs,
+		}
+		opts := tspclient.RequestOptions{
+			Content:       []byte("notation"),
+			HashAlgorithm: crypto.SHA256,
+		}
+		expectedErr := "invalid timestamping response: invalid response with status code 2: rejected"
+		_, err = Timestamp(req, opts)
+		assertErrorEqual(expectedErr, err, t)
+	})
+
+	t.Run("Timestamping with cms verification failure", func(t *testing.T) {
+		opts := tspclient.RequestOptions{
+			Content:       []byte("notation"),
+			HashAlgorithm: crypto.SHA256,
+		}
+		req := &signature.SignRequest{
+			Timestamper: dummyTimestamper{
+				invalidSignature: true,
+			},
+			TSARootCAs: rootCAs,
+		}
+		expectedErr := "failed to verify signed token: cms verification failure: x509: certificate signed by unknown authority"
+		_, err = Timestamp(req, opts)
+		assertErrorEqual(expectedErr, err, t)
+	})
+
+	t.Run("Timestamping revocation failed", func(t *testing.T) {
+		timestamper, err := tspclient.NewHTTPTimestamper(nil, rfc3161TSAurl)
+		if err != nil {
+			t.Fatal(err)
+		}
+		req := &signature.SignRequest{
+			Timestamper: timestamper,
+			TSARootCAs:  rootCAs,
+			TSARevocationValidator: &dummyTSARevocationValidator{
+				failOnValidate: true,
+			},
+		}
+		opts := tspclient.RequestOptions{
+			Content:       []byte("notation"),
+			HashAlgorithm: crypto.SHA256,
+		}
+		expectedErr := "failed to validate the revocation status of timestamping certificate chain with error: failed in ValidateContext"
+		_, err = Timestamp(req, opts)
+		assertErrorEqual(expectedErr, err, t)
+	})
+
+	t.Run("Timestamping certificate revoked", func(t *testing.T) {
+		timestamper, err := tspclient.NewHTTPTimestamper(nil, rfc3161TSAurl)
+		if err != nil {
+			t.Fatal(err)
+		}
+		req := &signature.SignRequest{
+			Timestamper: timestamper,
+			TSARootCAs:  rootCAs,
+			TSARevocationValidator: &dummyTSARevocationValidator{
+				revoked: true,
+			},
+		}
+		opts := tspclient.RequestOptions{
+			Content:       []byte("notation"),
+			HashAlgorithm: crypto.SHA256,
+		}
+		expectedErr := `timestamping certificate with subject "CN=DigiCert Timestamp 2024,O=DigiCert,C=US" is revoked`
+		_, err = Timestamp(req, opts)
+		assertErrorEqual(expectedErr, err, t)
+	})
+
+}
+
+func TestRevocationResult(t *testing.T) {
+	certResult := []*result.CertRevocationResult{
+		{
+			// update leaf cert result in each sub-test
+		},
+		{
+			Result: result.ResultNonRevokable,
+			ServerResults: []*result.ServerResult{
+				{
+					Result: result.ResultNonRevokable,
+				},
+			},
+		},
+	}
+	certChain := []*x509.Certificate{
+		{
+			Subject: pkix.Name{
+				CommonName: "leafCert",
+			},
+		},
+		{
+			Subject: pkix.Name{
+				CommonName: "rootCert",
+			},
+		},
+	}
+	t.Run("OCSP error without fallback", func(t *testing.T) {
+		certResult[0] = &result.CertRevocationResult{
+			Result: result.ResultUnknown,
+			ServerResults: []*result.ServerResult{
+				{
+					Result:           result.ResultUnknown,
+					Error:            errors.New("ocsp error"),
+					RevocationMethod: result.RevocationMethodOCSP,
+				},
+			},
+		}
+		err := revocationResult(certResult, certChain)
+		assertErrorEqual(`timestamping certificate with subject "CN=leafCert" revocation status is unknown`, err, t)
+	})
+
+	t.Run("OCSP error with fallback", func(t *testing.T) {
+		certResult[0] = &result.CertRevocationResult{
+			Result: result.ResultOK,
+			ServerResults: []*result.ServerResult{
+				{
+					Result:           result.ResultUnknown,
+					Error:            errors.New("ocsp error"),
+					RevocationMethod: result.RevocationMethodOCSP,
+				},
+				{
+					Result:           result.ResultOK,
+					RevocationMethod: result.RevocationMethodCRL,
+				},
+			},
+			RevocationMethod: result.RevocationMethodOCSPFallbackCRL,
+		}
+		if err := revocationResult(certResult, certChain); err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	t.Run("OCSP error with fallback and CRL error", func(t *testing.T) {
+		certResult[0] = &result.CertRevocationResult{
+			Result: result.ResultUnknown,
+			ServerResults: []*result.ServerResult{
+				{
+					Result:           result.ResultUnknown,
+					Error:            errors.New("ocsp error"),
+					RevocationMethod: result.RevocationMethodOCSP,
+				},
+				{
+					Result:           result.ResultUnknown,
+					Error:            errors.New("crl error"),
+					RevocationMethod: result.RevocationMethodCRL,
+				},
+			},
+			RevocationMethod: result.RevocationMethodOCSPFallbackCRL,
+		}
+		err := revocationResult(certResult, certChain)
+		assertErrorEqual(`timestamping certificate with subject "CN=leafCert" revocation status is unknown`, err, t)
+	})
+
+	t.Run("revoked", func(t *testing.T) {
+		certResult[0] = &result.CertRevocationResult{
+			Result: result.ResultRevoked,
+			ServerResults: []*result.ServerResult{
+				{
+					Result:           result.ResultRevoked,
+					Error:            errors.New("revoked"),
+					RevocationMethod: result.RevocationMethodCRL,
+				},
+			},
+		}
+		err := revocationResult(certResult, certChain)
+		assertErrorEqual(`timestamping certificate with subject "CN=leafCert" is revoked`, err, t)
+	})
+
+	t.Run("revocation method unknown error(should never reach here)", func(t *testing.T) {
+		certResult[0] = &result.CertRevocationResult{
+			Result: result.ResultUnknown,
+			ServerResults: []*result.ServerResult{
+				{
+					Result:           result.ResultUnknown,
+					Error:            errors.New("unknown error"),
+					RevocationMethod: result.RevocationMethodUnknown,
+				},
+			},
+		}
+		err := revocationResult(certResult, certChain)
+		assertErrorEqual(`timestamping certificate with subject "CN=leafCert" revocation status is unknown`, err, t)
+	})
+
+	t.Run("empty cert result", func(t *testing.T) {
+		err := revocationResult([]*result.CertRevocationResult{}, certChain)
+		assertErrorEqual("certificate revocation result cannot be empty", err, t)
+	})
+
+	t.Run("cert result length does not equal to cert chain", func(t *testing.T) {
+		err := revocationResult([]*result.CertRevocationResult{
+			certResult[1],
+		}, certChain)
+		assertErrorEqual("length of certificate revocation result 1 does not match length of the certificate chain 2", err, t)
+	})
+
+}
+
+func assertErrorEqual(expected string, err error, t *testing.T) {
+	if err == nil || expected != err.Error() {
+		t.Fatalf("Expected error \"%v\" but was \"%v\"", expected, err)
+	}
+}
+
+type dummyTimestamper struct {
+	respWithRejectedStatus bool
+	invalidSignature       bool
+}
+
+func (d dummyTimestamper) Timestamp(context.Context, *tspclient.Request) (*tspclient.Response, error) {
+	if d.respWithRejectedStatus {
+		return &tspclient.Response{
+			Status: pki.StatusInfo{
+				Status: pki.StatusRejection,
+			},
+		}, nil
+	}
+	if d.invalidSignature {
+		token, err := os.ReadFile("testdata/TimeStampTokenWithInvalidSignature.p7s")
+		if err != nil {
+			return nil, err
+		}
+		return &tspclient.Response{
+			Status: pki.StatusInfo{
+				Status: pki.StatusGranted,
+			},
+			TimestampToken: asn1.RawValue{
+				FullBytes: token,
+			},
+		}, nil
+	}
+	return nil, errors.New("failed to timestamp")
+}
+
+type dummyTSARevocationValidator struct {
+	failOnValidate bool
+	revoked        bool
+}
+
+func (v *dummyTSARevocationValidator) ValidateContext(ctx context.Context, validateContextOpts revocation.ValidateContextOptions) ([]*result.CertRevocationResult, error) {
+	if v.failOnValidate {
+		return nil, errors.New("failed in ValidateContext")
+	}
+	if v.revoked {
+		certResults := make([]*result.CertRevocationResult, len(validateContextOpts.CertChain))
+		for i := range certResults {
+			certResults[i] = &result.CertRevocationResult{
+				Result: result.ResultOK,
+				ServerResults: []*result.ServerResult{
+					{
+						Result:           result.ResultOK,
+						RevocationMethod: result.RevocationMethodOCSP,
+					},
+				},
+			}
+		}
+		certResults[0] = &result.CertRevocationResult{
+			Result: result.ResultRevoked,
+			ServerResults: []*result.ServerResult{
+				{
+					Result:           result.ResultRevoked,
+					Error:            errors.New("revoked"),
+					RevocationMethod: result.RevocationMethodCRL,
+				},
+			},
+		}
+		certResults[len(certResults)-1] = &result.CertRevocationResult{
+			Result: result.ResultNonRevokable,
+			ServerResults: []*result.ServerResult{
+				{
+					Result: result.ResultNonRevokable,
+				},
+			},
+		}
+		return certResults, nil
+	}
+	return nil, nil
+}

revocation/crl/bundle.go

@@ -0,0 +1,28 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package crl
+
+import "crypto/x509"
+
+// Bundle is a collection of CRLs, including base and delta CRLs
+type Bundle struct {
+	// BaseCRL is the parsed base CRL
+	BaseCRL *x509.RevocationList
+
+	// DeltaCRL is the parsed delta CRL
+	//
+	// TODO: support delta CRL https://github.com/notaryproject/notation-core-go/issues/228
+	// It will always be nil until we support delta CRL
+	DeltaCRL *x509.RevocationList
+}

revocation/crl/cache.go

@@ -0,0 +1,32 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package crl
+
+import "context"
+
+// Cache is an interface that specifies methods used for caching
+type Cache interface {
+	// Get retrieves the CRL bundle with the given url
+	//
+	// url is the key to retrieve the CRL bundle
+	//
+	// if the key does not exist or the content is expired, return ErrCacheMiss.
+	Get(ctx context.Context, url string) (*Bundle, error)
+
+	// Set stores the CRL bundle with the given url
+	//
+	// url is the key to store the CRL bundle
+	// bundle is the CRL collections to store
+	Set(ctx context.Context, url string, bundle *Bundle) error
+}

revocation/crl/errors.go

@@ -0,0 +1,22 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package crl
+
+import "errors"
+
+// ErrCacheMiss is returned when a cache miss occurs.
+var ErrCacheMiss = errors.New("cache miss")
+
+// errDeltaCRLNotFound is returned when a delta CRL is not found.
+var errDeltaCRLNotFound = errors.New("delta CRL not found")

revocation/crl/fetcher.go

@@ -0,0 +1,266 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package crl provides Fetcher interface with its implementation, and the
+// Cache interface.
+package crl
+
+import (
+	"context"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/asn1"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"time"
+
+	"github.com/notaryproject/notation-core-go/revocation/internal/x509util"
+	"golang.org/x/crypto/cryptobyte"
+	cbasn1 "golang.org/x/crypto/cryptobyte/asn1"
+)
+
+// oidFreshestCRL is the object identifier for the distribution point
+// for the delta CRL. (See RFC 5280, Section 5.2.6)
+var oidFreshestCRL = asn1.ObjectIdentifier{2, 5, 29, 46}
+
+// maxCRLSize is the maximum size of CRL in bytes
+//
+// The 32 MiB limit is based on investigation that even the largest CRLs
+// are less than 16 MiB. The limit is set to 32 MiB to prevent
+const maxCRLSize = 32 * 1024 * 1024 // 32 MiB
+
+// Fetcher is an interface that specifies methods used for fetching CRL
+// from the given URL
+type Fetcher interface {
+	// Fetch retrieves the CRL from the given URL.
+	Fetch(ctx context.Context, url string) (*Bundle, error)
+}
+
+// HTTPFetcher is a Fetcher implementation that fetches CRL from the given URL
+type HTTPFetcher struct {
+	// Cache stores fetched CRLs and reuses them until the CRL reaches the
+	// NextUpdate time.
+	// If Cache is nil, no cache is used.
+	Cache Cache
+
+	// DiscardCacheError specifies whether to discard any error on cache.
+	//
+	// ErrCacheMiss is not considered as an failure and will not be returned as
+	// an error if DiscardCacheError is false.
+	DiscardCacheError bool
+
+	httpClient *http.Client
+}
+
+// NewHTTPFetcher creates a new HTTPFetcher with the given HTTP client
+func NewHTTPFetcher(httpClient *http.Client) (*HTTPFetcher, error) {
+	if httpClient == nil {
+		return nil, errors.New("httpClient cannot be nil")
+	}
+
+	return &HTTPFetcher{
+		httpClient: httpClient,
+	}, nil
+}
+
+// Fetch retrieves the CRL from the given URL
+//
+// If cache is not nil, try to get the CRL from the cache first. On failure
+// (e.g. cache miss), it will download the CRL from the URL and store it to the
+// cache.
+func (f *HTTPFetcher) Fetch(ctx context.Context, url string) (*Bundle, error) {
+	if url == "" {
+		return nil, errors.New("CRL URL cannot be empty")
+	}
+
+	if f.Cache != nil {
+		bundle, err := f.Cache.Get(ctx, url)
+		if err == nil {
+			// check expiry of base CRL and delta CRL
+			if isEffective(bundle.BaseCRL) && (bundle.DeltaCRL == nil || isEffective(bundle.DeltaCRL)) {
+				return bundle, nil
+			}
+		} else if !errors.Is(err, ErrCacheMiss) && !f.DiscardCacheError {
+			return nil, fmt.Errorf("failed to retrieve CRL from cache: %w", err)
+		}
+	}
+
+	bundle, err := f.fetch(ctx, url)
+	if err != nil {
+		return nil, fmt.Errorf("failed to retrieve CRL: %w", err)
+	}
+
+	if f.Cache != nil {
+		err = f.Cache.Set(ctx, url, bundle)
+		if err != nil && !f.DiscardCacheError {
+			return nil, fmt.Errorf("failed to store CRL to cache: %w", err)
+		}
+	}
+
+	return bundle, nil
+}
+
+// isEffective checks if the CRL is effective by checking the NextUpdate time.
+func isEffective(crl *x509.RevocationList) bool {
+	return !crl.NextUpdate.IsZero() && !time.Now().After(crl.NextUpdate)
+}
+
+// fetch downloads the CRL from the given URL.
+func (f *HTTPFetcher) fetch(ctx context.Context, url string) (*Bundle, error) {
+	// fetch base CRL
+	base, err := fetchCRL(ctx, url, f.httpClient)
+	if err != nil {
+		return nil, err
+	}
+
+	// fetch delta CRL from base CRL extension
+	deltaCRL, err := f.fetchDeltaCRL(ctx, base.Extensions)
+	if err != nil && !errors.Is(err, errDeltaCRLNotFound) {
+		return nil, err
+	}
+
+	return &Bundle{
+		BaseCRL:  base,
+		DeltaCRL: deltaCRL,
+	}, nil
+}
+
+// fetchDeltaCRL fetches the delta CRL from the given extensions of base CRL.
+//
+// It returns errDeltaCRLNotFound if the delta CRL is not found.
+func (f *HTTPFetcher) fetchDeltaCRL(ctx context.Context, extensions []pkix.Extension) (*x509.RevocationList, error) {
+	extension := x509util.FindExtensionByOID(extensions, oidFreshestCRL)
+	if extension == nil {
+		return nil, errDeltaCRLNotFound
+	}
+
+	// RFC 5280, 4.2.1.15
+	//    id-ce-freshestCRL OBJECT IDENTIFIER ::=  { id-ce 46 }
+	//
+	//    FreshestCRL ::= CRLDistributionPoints
+	urls, err := parseCRLDistributionPoint(extension.Value)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse Freshest CRL extension: %w", err)
+	}
+	if len(urls) == 0 {
+		return nil, errDeltaCRLNotFound
+	}
+
+	var (
+		lastError error
+		deltaCRL  *x509.RevocationList
+	)
+	for _, cdpURL := range urls {
+		// RFC 5280, 5.2.6
+		// Delta CRLs from the base CRL have the same scope as the base
+		// CRL, so the URLs are for redundancy and should be tried in
+		// order until one succeeds.
+		deltaCRL, lastError = fetchCRL(ctx, cdpURL, f.httpClient)
+		if lastError == nil {
+			return deltaCRL, nil
+		}
+	}
+	return nil, lastError
+}
+
+// parseCRLDistributionPoint parses the CRL extension and returns the CRL URLs
+//
+// value is the raw value of the CRL distribution point extension
+func parseCRLDistributionPoint(value []byte) ([]string, error) {
+	var urls []string
+	// borrowed from crypto/x509: https://cs.opensource.google/go/go/+/refs/tags/go1.23.4:src/crypto/x509/parser.go;l=700-743
+	//
+	// RFC 5280, 4.2.1.13
+	//
+	// CRLDistributionPoints ::= SEQUENCE SIZE (1..MAX) OF DistributionPoint
+	//
+	// DistributionPoint ::= SEQUENCE {
+	//     distributionPoint       [0]     DistributionPointName OPTIONAL,
+	//     reasons                 [1]     ReasonFlags OPTIONAL,
+	//     cRLIssuer               [2]     GeneralNames OPTIONAL }
+	//
+	// DistributionPointName ::= CHOICE {
+	//     fullName                [0]     GeneralNames,
+	//     nameRelativeToCRLIssuer [1]     RelativeDistinguishedName }
+	val := cryptobyte.String(value)
+	if !val.ReadASN1(&val, cbasn1.SEQUENCE) {
+		return nil, errors.New("x509: invalid CRL distribution points")
+	}
+	for !val.Empty() {
+		var dpDER cryptobyte.String
+		if !val.ReadASN1(&dpDER, cbasn1.SEQUENCE) {
+			return nil, errors.New("x509: invalid CRL distribution point")
+		}
+		var dpNameDER cryptobyte.String
+		var dpNamePresent bool
+		if !dpDER.ReadOptionalASN1(&dpNameDER, &dpNamePresent, cbasn1.Tag(0).Constructed().ContextSpecific()) {
+			return nil, errors.New("x509: invalid CRL distribution point")
+		}
+		if !dpNamePresent {
+			continue
+		}
+		if !dpNameDER.ReadASN1(&dpNameDER, cbasn1.Tag(0).Constructed().ContextSpecific()) {
+			return nil, errors.New("x509: invalid CRL distribution point")
+		}
+		for !dpNameDER.Empty() {
+			if !dpNameDER.PeekASN1Tag(cbasn1.Tag(6).ContextSpecific()) {
+				break
+			}
+			var uri cryptobyte.String
+			if !dpNameDER.ReadASN1(&uri, cbasn1.Tag(6).ContextSpecific()) {
+				return nil, errors.New("x509: invalid CRL distribution point")
+			}
+			urls = append(urls, string(uri))
+		}
+	}
+	return urls, nil
+}
+
+func fetchCRL(ctx context.Context, crlURL string, client *http.Client) (*x509.RevocationList, error) {
+	// validate URL
+	parsedURL, err := url.Parse(crlURL)
+	if err != nil {
+		return nil, fmt.Errorf("invalid CRL URL: %w", err)
+	}
+	if parsedURL.Scheme != "http" {
+		return nil, fmt.Errorf("unsupported scheme: %s. Only supports CRL URL in HTTP protocol", parsedURL.Scheme)
+	}
+
+	// download CRL
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, crlURL, nil)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create CRL request: %w", err)
+	}
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("request failed: %w", err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("failed to download with status code: %d", resp.StatusCode)
+	}
+	// read with size limit
+	data, err := io.ReadAll(io.LimitReader(resp.Body, maxCRLSize))
+	if err != nil {
+		return nil, fmt.Errorf("failed to read CRL response: %w", err)
+	}
+	if len(data) == maxCRLSize {
+		return nil, fmt.Errorf("CRL size exceeds the limit: %d", maxCRLSize)
+	}
+
+	// parse CRL
+	return x509.ParseRevocationList(data)
+}

revocation/crl/fetcher_test.go

@@ -0,0 +1,638 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package crl
+
+import (
+	"bytes"
+	"context"
+	"crypto/rand"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/pem"
+	"errors"
+	"fmt"
+	"io"
+	"math/big"
+	"net/http"
+	"os"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/notaryproject/notation-core-go/testhelper"
+)
+
+func TestNewHTTPFetcher(t *testing.T) {
+	t.Run("httpClient is nil", func(t *testing.T) {
+		_, err := NewHTTPFetcher(nil)
+		if err.Error() != "httpClient cannot be nil" {
+			t.Errorf("NewHTTPFetcher() error = %v, want %v", err, "httpClient cannot be nil")
+		}
+	})
+}
+
+func TestFetch(t *testing.T) {
+	// prepare crl
+	certChain := testhelper.GetRevokableRSAChainWithRevocations(2, false, true)
+	crlBytes, err := x509.CreateRevocationList(rand.Reader, &x509.RevocationList{
+		Number:     big.NewInt(1),
+		NextUpdate: time.Now().Add(1 * time.Hour),
+	}, certChain[1].Cert, certChain[1].PrivateKey)
+	if err != nil {
+		t.Fatalf("failed to create base CRL: %v", err)
+	}
+	baseCRL, err := x509.ParseRevocationList(crlBytes)
+	if err != nil {
+		t.Fatalf("failed to parse base CRL: %v", err)
+	}
+	const exampleURL = "http://localhost.test"
+	const uncachedURL = "http://uncached.test"
+
+	bundle := &Bundle{
+		BaseCRL: baseCRL,
+	}
+
+	t.Run("url is empty", func(t *testing.T) {
+		c := &memoryCache{}
+		httpClient := &http.Client{}
+		f, err := NewHTTPFetcher(httpClient)
+		if err != nil {
+			t.Errorf("NewHTTPFetcher() error = %v, want nil", err)
+		}
+		f.Cache = c
+		_, err = f.Fetch(context.Background(), "")
+		if err.Error() != "CRL URL cannot be empty" {
+			t.Fatalf("Fetcher.Fetch() error = %v, want CRL URL cannot be empty", err)
+		}
+	})
+
+	t.Run("fetch without cache", func(t *testing.T) {
+		httpClient := &http.Client{
+			Transport: &expectedRoundTripperMock{Body: baseCRL.Raw},
+		}
+		f, err := NewHTTPFetcher(httpClient)
+		if err != nil {
+			t.Errorf("NewHTTPFetcher() error = %v, want nil", err)
+		}
+		bundle, err := f.Fetch(context.Background(), exampleURL)
+		if err != nil {
+			t.Errorf("Fetcher.Fetch() error = %v, want nil", err)
+		}
+		if !bytes.Equal(bundle.BaseCRL.Raw, baseCRL.Raw) {
+			t.Errorf("Fetcher.Fetch() base.Raw = %v, want %v", bundle.BaseCRL.Raw, baseCRL.Raw)
+		}
+	})
+
+	t.Run("cache hit", func(t *testing.T) {
+		// set the cache
+		c := &memoryCache{}
+		if err := c.Set(context.Background(), exampleURL, bundle); err != nil {
+			t.Errorf("Cache.Set() error = %v, want nil", err)
+		}
+
+		httpClient := &http.Client{}
+		f, err := NewHTTPFetcher(httpClient)
+		if err != nil {
+			t.Errorf("NewHTTPFetcher() error = %v, want nil", err)
+		}
+		f.Cache = c
+		bundle, err := f.Fetch(context.Background(), exampleURL)
+		if err != nil {
+			t.Errorf("Fetcher.Fetch() error = %v, want nil", err)
+		}
+		if !bytes.Equal(bundle.BaseCRL.Raw, baseCRL.Raw) {
+			t.Errorf("Fetcher.Fetch() base.Raw = %v, want %v", bundle.BaseCRL.Raw, baseCRL.Raw)
+		}
+	})
+
+	t.Run("cache miss and download failed error", func(t *testing.T) {
+		c := &memoryCache{}
+		httpClient := &http.Client{
+			Transport: errorRoundTripperMock{},
+		}
+		f, err := NewHTTPFetcher(httpClient)
+		f.Cache = c
+		if err != nil {
+			t.Errorf("NewHTTPFetcher() error = %v, want nil", err)
+		}
+		_, err = f.Fetch(context.Background(), uncachedURL)
+		if err == nil {
+			t.Errorf("Fetcher.Fetch() error = nil, want not nil")
+		}
+	})
+
+	t.Run("cache miss", func(t *testing.T) {
+		c := &memoryCache{}
+		httpClient := &http.Client{
+			Transport: &expectedRoundTripperMock{Body: baseCRL.Raw},
+		}
+		f, err := NewHTTPFetcher(httpClient)
+		if err != nil {
+			t.Errorf("NewHTTPFetcher() error = %v, want nil", err)
+		}
+		f.Cache = c
+		f.DiscardCacheError = false
+		bundle, err := f.Fetch(context.Background(), uncachedURL)
+		if err != nil {
+			t.Errorf("Fetcher.Fetch() error = %v, want nil", err)
+		}
+		if !bytes.Equal(bundle.BaseCRL.Raw, baseCRL.Raw) {
+			t.Errorf("Fetcher.Fetch() base.Raw = %v, want %v", bundle.BaseCRL.Raw, baseCRL.Raw)
+		}
+	})
+
+	t.Run("cache expired", func(t *testing.T) {
+		c := &memoryCache{}
+		// prepare an expired CRL
+		certChain := testhelper.GetRevokableRSAChainWithRevocations(2, false, true)
+		expiredCRLBytes, err := x509.CreateRevocationList(rand.Reader, &x509.RevocationList{
+			Number:     big.NewInt(1),
+			NextUpdate: time.Now().Add(-1 * time.Hour),
+		}, certChain[1].Cert, certChain[1].PrivateKey)
+		if err != nil {
+			t.Fatalf("failed to create base CRL: %v", err)
+		}
+		expiredCRL, err := x509.ParseRevocationList(expiredCRLBytes)
+		if err != nil {
+			t.Fatalf("failed to parse base CRL: %v", err)
+		}
+		// store the expired CRL
+		const expiredCRLURL = "http://localhost.test/expired"
+		bundle := &Bundle{
+			BaseCRL: expiredCRL,
+		}
+		if err := c.Set(context.Background(), expiredCRLURL, bundle); err != nil {
+			t.Errorf("Cache.Set() error = %v, want nil", err)
+		}
+
+		// fetch the expired CRL
+		httpClient := &http.Client{
+			Transport: &expectedRoundTripperMock{Body: baseCRL.Raw},
+		}
+		f, err := NewHTTPFetcher(httpClient)
+		if err != nil {
+			t.Errorf("NewHTTPFetcher() error = %v, want nil", err)
+		}
+		f.Cache = c
+		f.DiscardCacheError = true
+		bundle, err = f.Fetch(context.Background(), expiredCRLURL)
+		if err != nil {
+			t.Errorf("Fetcher.Fetch() error = %v, want nil", err)
+		}
+		// should re-download the CRL
+		if !bytes.Equal(bundle.BaseCRL.Raw, baseCRL.Raw) {
+			t.Errorf("Fetcher.Fetch() base.Raw = %v, want %v", bundle.BaseCRL.Raw, baseCRL.Raw)
+		}
+	})
+
+	t.Run("Set cache error", func(t *testing.T) {
+		c := &errorCache{
+			GetError: ErrCacheMiss,
+			SetError: errors.New("cache error"),
+		}
+		httpClient := &http.Client{
+			Transport: &expectedRoundTripperMock{Body: baseCRL.Raw},
+		}
+		f, err := NewHTTPFetcher(httpClient)
+		if err != nil {
+			t.Errorf("NewHTTPFetcher() error = %v, want nil", err)
+		}
+		f.Cache = c
+		f.DiscardCacheError = true
+		bundle, err = f.Fetch(context.Background(), exampleURL)
+		if err != nil {
+			t.Errorf("Fetcher.Fetch() error = %v, want nil", err)
+		}
+		if !bytes.Equal(bundle.BaseCRL.Raw, baseCRL.Raw) {
+			t.Errorf("Fetcher.Fetch() base.Raw = %v, want %v", bundle.BaseCRL.Raw, baseCRL.Raw)
+		}
+	})
+
+	t.Run("Get error without discard", func(t *testing.T) {
+		c := &errorCache{
+			GetError: errors.New("cache error"),
+		}
+		httpClient := &http.Client{
+			Transport: &expectedRoundTripperMock{Body: baseCRL.Raw},
+		}
+		f, err := NewHTTPFetcher(httpClient)
+		if err != nil {
+			t.Errorf("NewHTTPFetcher() error = %v, want nil", err)
+		}
+		f.Cache = c
+		f.DiscardCacheError = false
+		_, err = f.Fetch(context.Background(), exampleURL)
+		if !strings.HasPrefix(err.Error(), "failed to retrieve CRL from cache:") {
+			t.Errorf("Fetcher.Fetch() error = %v, want failed to retrieve CRL from cache:", err)
+		}
+	})
+
+	t.Run("Set error without discard", func(t *testing.T) {
+		c := &errorCache{
+			GetError: ErrCacheMiss,
+			SetError: errors.New("cache error"),
+		}
+		httpClient := &http.Client{
+			Transport: &expectedRoundTripperMock{Body: baseCRL.Raw},
+		}
+		f, err := NewHTTPFetcher(httpClient)
+		if err != nil {
+			t.Errorf("NewHTTPFetcher() error = %v, want nil", err)
+		}
+		f.Cache = c
+		f.DiscardCacheError = false
+		_, err = f.Fetch(context.Background(), exampleURL)
+		if !strings.HasPrefix(err.Error(), "failed to store CRL to cache:") {
+			t.Errorf("Fetcher.Fetch() error = %v, want failed to store CRL to cache:", err)
+		}
+	})
+
+	t.Run("test fetch delta CRL from base CRL extension failed", func(t *testing.T) {
+		crlWithDeltaCRL, err := os.ReadFile("testdata/crlWithMultipleFreshestCRLs.crl")
+		if err != nil {
+			t.Fatalf("failed to read CRL: %v", err)
+		}
+		httpClient := &http.Client{
+			Transport: &expectedRoundTripperMock{
+				Body:            crlWithDeltaCRL,
+				SecondRoundBody: []byte("invalid crl"),
+			},
+		}
+		f, err := NewHTTPFetcher(httpClient)
+		if err != nil {
+			t.Errorf("NewHTTPFetcher() error = %v, want nil", err)
+		}
+		_, err = f.Fetch(context.Background(), exampleURL)
+		expectedErrorMsg := "failed to retrieve CRL: x509: malformed crl"
+		if err == nil || err.Error() != expectedErrorMsg {
+			t.Fatalf("expected error %q, got %v", expectedErrorMsg, err)
+		}
+	})
+}
+
+func TestParseFreshestCRL(t *testing.T) {
+	loadExtentsion := func(certPath string) pkix.Extension {
+		certData, err := os.ReadFile(certPath)
+		if err != nil {
+			t.Fatalf("failed to read certificate: %v", err)
+		}
+
+		block, _ := pem.Decode(certData)
+		if block == nil {
+			t.Fatalf("failed to decode PEM block")
+		}
+
+		cert, err := x509.ParseCertificate(block.Bytes)
+		if err != nil {
+			t.Fatalf("failed to parse certificate: %v", err)
+		}
+
+		for _, ext := range cert.Extensions {
+			if ext.Id.Equal([]int{2, 5, 29, 46}) { // id-ce-freshestCRL
+				return ext
+			}
+		}
+
+		t.Fatalf("freshestCRL extension not found")
+		return pkix.Extension{}
+	}
+
+	t.Run("valid 1 delta CRL URL", func(t *testing.T) {
+		certPath := "testdata/certificateWithDeltaCRL.cer"
+		freshestCRLExtension := loadExtentsion(certPath)
+		urls, err := parseCRLDistributionPoint(freshestCRLExtension.Value)
+		if err != nil {
+			t.Fatalf("failed to parse freshest CRL: %v", err)
+		}
+
+		if len(urls) != 1 {
+			t.Fatalf("expected 1 URL, got %d", len(urls))
+		}
+
+		if !strings.HasPrefix(urls[0], "http://localhost:80") {
+			t.Fatalf("unexpected URL: %s", urls[0])
+		}
+	})
+
+	t.Run("empty extension", func(t *testing.T) {
+		_, err := parseCRLDistributionPoint(nil)
+		if err == nil {
+			t.Fatalf("expected error")
+		}
+	})
+
+	t.Run("URL doesn't exist", func(t *testing.T) {
+		certPath := "testdata/certificateWithZeroDeltaCRLURL.cer"
+		freshestCRLExtension := loadExtentsion(certPath)
+		url, err := parseCRLDistributionPoint(freshestCRLExtension.Value)
+		if err != nil {
+			t.Fatalf("failed to parse freshest CRL: %v", err)
+		}
+		if len(url) != 0 {
+			t.Fatalf("expected 0 URL, got %d", len(url))
+		}
+	})
+
+	t.Run("non URI freshest CRL extension", func(t *testing.T) {
+		certPath := "testdata/certificateWithNonURIDeltaCRL.cer"
+		freshestCRLExtension := loadExtentsion(certPath)
+		url, err := parseCRLDistributionPoint(freshestCRLExtension.Value)
+		if err != nil {
+			t.Fatalf("failed to parse freshest CRL: %v", err)
+		}
+		if len(url) != 0 {
+			t.Fatalf("expected 0 URL, got %d", len(url))
+		}
+	})
+
+	t.Run("certificate with incomplete freshest CRL extension", func(t *testing.T) {
+		certPath := "testdata/certificateWithIncompleteFreshestCRL.cer"
+		freshestCRLExtension := loadExtentsion(certPath)
+		_, err := parseCRLDistributionPoint(freshestCRLExtension.Value)
+		expectErrorMsg := "x509: invalid CRL distribution point"
+		if err == nil || err.Error() != expectErrorMsg {
+			t.Fatalf("expected error %q, got %v", expectErrorMsg, err)
+		}
+	})
+
+	t.Run("certificate with incomplete freshest CRL extension2", func(t *testing.T) {
+		certPath := "testdata/certificateWithIncompleteFreshestCRL2.cer"
+		freshestCRLExtension := loadExtentsion(certPath)
+		url, err := parseCRLDistributionPoint(freshestCRLExtension.Value)
+		if err != nil {
+			t.Fatalf("failed to parse freshest CRL: %v", err)
+		}
+		if len(url) != 0 {
+			t.Fatalf("expected 0 URL, got %d", len(url))
+		}
+	})
+}
+
+func TestFetchDeltaCRL(t *testing.T) {
+	loadExtentsion := func(certPath string) []pkix.Extension {
+		certData, err := os.ReadFile(certPath)
+		if err != nil {
+			t.Fatalf("failed to read certificate: %v", err)
+		}
+
+		block, _ := pem.Decode(certData)
+		if block == nil {
+			t.Fatalf("failed to decode PEM block")
+		}
+
+		cert, err := x509.ParseCertificate(block.Bytes)
+		if err != nil {
+			t.Fatalf("failed to parse certificate: %v", err)
+		}
+
+		return cert.Extensions
+	}
+
+	deltaCRL, err := os.ReadFile("testdata/delta.crl")
+	if err != nil {
+		t.Fatalf("failed to read delta CRL: %v", err)
+	}
+
+	fetcher, err := NewHTTPFetcher(&http.Client{
+		Transport: &expectedRoundTripperMock{Body: deltaCRL},
+	})
+	if err != nil {
+		t.Fatalf("failed to create fetcher: %v", err)
+	}
+
+	t.Run("parse freshest CRL failed", func(t *testing.T) {
+		certPath := "testdata/certificateWithIncompleteFreshestCRL.cer"
+		extensions := loadExtentsion(certPath)
+		_, err := fetcher.fetchDeltaCRL(context.Background(), extensions)
+		expectedErrorMsg := "failed to parse Freshest CRL extension: x509: invalid CRL distribution point"
+		if err == nil || err.Error() != expectedErrorMsg {
+			t.Fatalf("expected error %q, got %v", expectedErrorMsg, err)
+		}
+	})
+
+	t.Run("zero freshest CRL URL", func(t *testing.T) {
+		certPath := "testdata/certificateWithZeroDeltaCRLURL.cer"
+		extensions := loadExtentsion(certPath)
+		_, err := fetcher.fetchDeltaCRL(context.Background(), extensions)
+		expectedErr := errDeltaCRLNotFound
+		if err == nil || !errors.Is(err, expectedErr) {
+			t.Fatalf("expected error %v, got %v", expectedErr, err)
+		}
+	})
+
+	t.Run("one freshest CRL URL", func(t *testing.T) {
+		certPath := "testdata/certificateWithDeltaCRL.cer"
+		extensions := loadExtentsion(certPath)
+		deltaCRL, err := fetcher.fetchDeltaCRL(context.Background(), extensions)
+		if err != nil {
+			t.Fatalf("failed to process delta CRL: %v", err)
+		}
+		if deltaCRL == nil {
+			t.Fatalf("expected non-nil delta CRL")
+		}
+	})
+
+	t.Run("multiple freshest CRL URLs failed", func(t *testing.T) {
+		fetcherWithError, err := NewHTTPFetcher(&http.Client{
+			Transport: errorRoundTripperMock{},
+		})
+		if err != nil {
+			t.Fatalf("failed to create fetcher: %v", err)
+		}
+		certPath := "testdata/certificateWith2DeltaCRL.cer"
+		extensions := loadExtentsion(certPath)
+		_, err = fetcherWithError.fetchDeltaCRL(context.Background(), extensions)
+		expectedErrorMsg := "request failed"
+		if err == nil || !strings.Contains(err.Error(), expectedErrorMsg) {
+			t.Fatalf("expected error %q, got %v", expectedErrorMsg, err)
+		}
+	})
+
+	t.Run("process delta crl from certificate extension failed", func(t *testing.T) {
+		certPath := "testdata/certificateWithIncompleteFreshestCRL.cer"
+		extensions := loadExtentsion(certPath)
+		_, err := fetcher.fetchDeltaCRL(context.Background(), extensions)
+		expectedErrorMsg := "failed to parse Freshest CRL extension: x509: invalid CRL distribution point"
+		if err == nil || err.Error() != expectedErrorMsg {
+			t.Fatalf("expected error %q, got %v", expectedErrorMsg, err)
+		}
+	})
+}
+
+func TestDownload(t *testing.T) {
+	t.Run("parse url error", func(t *testing.T) {
+		_, err := fetchCRL(context.Background(), ":", http.DefaultClient)
+		if err == nil {
+			t.Fatal("expected error")
+		}
+	})
+	t.Run("https download", func(t *testing.T) {
+		_, err := fetchCRL(context.Background(), "https://localhost.test", http.DefaultClient)
+		if err == nil {
+			t.Fatal("expected error")
+		}
+	})
+
+	t.Run("http.NewRequestWithContext error", func(t *testing.T) {
+		var ctx context.Context = nil
+		_, err := fetchCRL(ctx, "http://localhost.test", &http.Client{})
+		if err == nil {
+			t.Fatal("expected error")
+		}
+	})
+
+	t.Run("client.Do error", func(t *testing.T) {
+		_, err := fetchCRL(context.Background(), "http://localhost.test", &http.Client{
+			Transport: errorRoundTripperMock{},
+		})
+
+		if err == nil {
+			t.Fatal("expected error")
+		}
+	})
+
+	t.Run("status code is not 2xx", func(t *testing.T) {
+		_, err := fetchCRL(context.Background(), "http://localhost.test", &http.Client{
+			Transport: serverErrorRoundTripperMock{},
+		})
+		if err == nil {
+			t.Fatal("expected error")
+		}
+	})
+
+	t.Run("readAll error", func(t *testing.T) {
+		_, err := fetchCRL(context.Background(), "http://localhost.test", &http.Client{
+			Transport: readFailedRoundTripperMock{},
+		})
+		if err == nil {
+			t.Fatal("expected error")
+		}
+	})
+
+	t.Run("exceed the size limit", func(t *testing.T) {
+		_, err := fetchCRL(context.Background(), "http://localhost.test", &http.Client{
+			Transport: &expectedRoundTripperMock{Body: make([]byte, maxCRLSize+1)},
+		})
+		if err == nil {
+			t.Fatal("expected error")
+		}
+	})
+
+	t.Run("invalid crl", func(t *testing.T) {
+		_, err := fetchCRL(context.Background(), "http://localhost.test", &http.Client{
+			Transport: &expectedRoundTripperMock{Body: []byte("invalid crl")},
+		})
+		if err == nil {
+			t.Fatal("expected error")
+		}
+	})
+}
+
+type errorRoundTripperMock struct{}
+
+func (rt errorRoundTripperMock) RoundTrip(req *http.Request) (*http.Response, error) {
+	return nil, fmt.Errorf("error")
+}
+
+type serverErrorRoundTripperMock struct{}
+
+func (rt serverErrorRoundTripperMock) RoundTrip(req *http.Request) (*http.Response, error) {
+	return &http.Response{
+		Request:    req,
+		StatusCode: http.StatusInternalServerError,
+	}, nil
+}
+
+type readFailedRoundTripperMock struct{}
+
+func (rt readFailedRoundTripperMock) RoundTrip(req *http.Request) (*http.Response, error) {
+	return &http.Response{
+		StatusCode: http.StatusOK,
+		Body:       errorReaderMock{},
+	}, nil
+}
+
+type errorReaderMock struct{}
+
+func (r errorReaderMock) Read(p []byte) (n int, err error) {
+	return 0, fmt.Errorf("error")
+}
+
+func (r errorReaderMock) Close() error {
+	return nil
+}
+
+type expectedRoundTripperMock struct {
+	Body            []byte
+	SecondRoundBody []byte
+	count           int
+}
+
+func (rt *expectedRoundTripperMock) RoundTrip(req *http.Request) (*http.Response, error) {
+	if rt.count == 0 {
+		rt.count += 1
+		return &http.Response{
+			Request:    req,
+			StatusCode: http.StatusOK,
+			Body:       io.NopCloser(bytes.NewBuffer(rt.Body)),
+		}, nil
+	}
+	return &http.Response{
+		Request:    req,
+		StatusCode: http.StatusOK,
+		Body:       io.NopCloser(bytes.NewBuffer(rt.SecondRoundBody)),
+	}, nil
+}
+
+// memoryCache is an in-memory cache that stores CRL bundles for testing.
+type memoryCache struct {
+	store sync.Map
+}
+
+// Get retrieves the CRL from the memory store.
+//
+// - if the key does not exist, return ErrNotFound
+// - if the CRL is expired, return ErrCacheMiss
+func (c *memoryCache) Get(ctx context.Context, url string) (*Bundle, error) {
+	value, ok := c.store.Load(url)
+	if !ok {
+		return nil, ErrCacheMiss
+	}
+	bundle, ok := value.(*Bundle)
+	if !ok {
+		return nil, fmt.Errorf("invalid type: %T", value)
+	}
+
+	return bundle, nil
+}
+
+// Set stores the CRL in the memory store.
+func (c *memoryCache) Set(ctx context.Context, url string, bundle *Bundle) error {
+	c.store.Store(url, bundle)
+	return nil
+}
+
+type errorCache struct {
+	GetError error
+	SetError error
+}
+
+func (c *errorCache) Get(ctx context.Context, url string) (*Bundle, error) {
+	return nil, c.GetError
+}
+
+func (c *errorCache) Set(ctx context.Context, url string, bundle *Bundle) error {
+	return c.SetError
+}

revocation/crl/testdata/certificateWith2DeltaCRL.cer

@@ -0,0 +1,32 @@
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+dRTSOVkICjWU
+-----END CERTIFICATE-----

revocation/crl/testdata/certificateWithDeltaCRL.cer

@@ -0,0 +1,28 @@
+-----BEGIN CERTIFICATE-----
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+ewhVgLUqtg/YqnmNYJp0u8jC7YHSPt4D4vA3YwFZ2WF1FNI5WQgKNZQ=
+-----END CERTIFICATE-----

revocation/crl/testdata/certificateWithIncompleteFreshestCRL.cer

@@ -0,0 +1,22 @@
+-----BEGIN CERTIFICATE-----
+MIIDmTCCAgGgAwIBAgIUaHnHWrIVx0qzAZIwvELkQUEs+3cwDQYJKoZIhvcNAQEL
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+AVnZYXUU0jlZCAo1lA==
+-----END CERTIFICATE-----

revocation/crl/testdata/certificateWithIncompleteFreshestCRL2.cer

@@ -0,0 +1,22 @@
+-----BEGIN CERTIFICATE-----
+MIIDlzCCAf+gAwIBAgIUaHnHWrIVx0qzAZIwvELkQUEs+3cwDQYJKoZIhvcNAQEL
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+2WF1FNI5WQgKNZQ=
+-----END CERTIFICATE-----

revocation/crl/testdata/certificateWithNonURIDeltaCRL.cer

@@ -0,0 +1,22 @@
+-----BEGIN CERTIFICATE-----
+MIIDnjCCAgagAwIBAgIUaHnHWrIVx0qzAZIwvELkQUEs+3cwDQYJKoZIhvcNAQEL
+BQAwYTEjMCEGCgmSJomT8ixkAQEME2MtMG53d296cXZhd3ZhbzNlY2gxFTATBgNV
+BAMMDE1hbmFnZW1lbnRDQTEjMCEGA1UECgwaRUpCQ0EgQ29udGFpbmVyIFF1aWNr
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+DA1Ob3RhdGlvblRlc3QzMIGbMBAGByqGSM49AgEGBSuBBAAjA4GGAAQAuJlXlrTm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+-----END CERTIFICATE-----

revocation/crl/testdata/certificateWithZeroDeltaCRLURL.cer

@@ -0,0 +1,25 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----

revocation/internal/crl/crl.go

@@ -0,0 +1,388 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package crl provides methods for checking the revocation status of a
+// certificate using CRL
+package crl
+
+import (
+	"context"
+	"crypto/x509"
+	"encoding/asn1"
+	"errors"
+	"fmt"
+	"math/big"
+	"time"
+
+	"github.com/notaryproject/notation-core-go/revocation/crl"
+	"github.com/notaryproject/notation-core-go/revocation/internal/x509util"
+	"github.com/notaryproject/notation-core-go/revocation/result"
+	"golang.org/x/crypto/cryptobyte"
+)
+
+// RFC 5280, 5.3.1
+//
+//	CRLReason ::= ENUMERATED {
+//	  unspecified             (0),
+//	  keyCompromise           (1),
+//	  cACompromise            (2),
+//	  affiliationChanged      (3),
+//	  superseded              (4),
+//	  cessationOfOperation    (5),
+//	  certificateHold         (6),
+//	       -- value 7 is not used
+//	  removeFromCRL           (8),
+//	  privilegeWithdrawn      (9),
+//	  aACompromise           (10) }
+const (
+	reasonCodeCertificateHold = 6 // certificateHold
+	reasonCodeRemoveFromCRL   = 8 // removeFromCRL
+)
+
+var (
+	// oidFreshestCRL is the object identifier for the distribution point
+	// for the delta CRL. (See RFC 5280, Section 5.2.6)
+	oidFreshestCRL = asn1.ObjectIdentifier{2, 5, 29, 46}
+
+	// oidIssuingDistributionPoint is the object identifier for the issuing
+	// distribution point CRL extension. (See RFC 5280, Section 5.2.5)
+	oidIssuingDistributionPoint = asn1.ObjectIdentifier{2, 5, 29, 28}
+
+	// oidDeltaCRLIndicator is the object identifier for the delta CRL indicator
+	// (See RFC 5280, Section 5.2.4)
+	oidDeltaCRLIndicator = asn1.ObjectIdentifier{2, 5, 29, 27}
+
+	// oidInvalidityDate is the object identifier for the invalidity date
+	// CRL entry extension. (See RFC 5280, Section 5.3.2)
+	oidInvalidityDate = asn1.ObjectIdentifier{2, 5, 29, 24}
+)
+
+// CertCheckStatusOptions specifies values that are needed to check CRL.
+type CertCheckStatusOptions struct {
+	// Fetcher is used to fetch the CRL from the CRL distribution points.
+	Fetcher crl.Fetcher
+
+	// SigningTime is used to compare with the invalidity date during revocation
+	// check.
+	SigningTime time.Time
+}
+
+// CertCheckStatus checks the revocation status of a certificate using CRL
+//
+// The function checks the revocation status of the certificate by downloading
+// the CRL from the CRL distribution points specified in the certificate.
+//
+// If the invalidity date extension is present in the CRL entry and SigningTime
+// is not zero, the certificate is considered revoked if the SigningTime is
+// after the invalidity date. (See RFC 5280, Section 5.3.2)
+func CertCheckStatus(ctx context.Context, cert, issuer *x509.Certificate, opts CertCheckStatusOptions) *result.CertRevocationResult {
+	if !Supported(cert) {
+		// CRL not enabled for this certificate.
+		return &result.CertRevocationResult{
+			Result: result.ResultNonRevokable,
+			ServerResults: []*result.ServerResult{{
+				RevocationMethod: result.RevocationMethodCRL,
+				Error:            errors.New("CRL is not supported"),
+				Result:           result.ResultNonRevokable,
+			}},
+			RevocationMethod: result.RevocationMethodCRL,
+		}
+	}
+
+	if opts.Fetcher == nil {
+		return &result.CertRevocationResult{
+			Result: result.ResultUnknown,
+			ServerResults: []*result.ServerResult{{
+				RevocationMethod: result.RevocationMethodCRL,
+				Error:            errors.New("CRL fetcher cannot be nil"),
+				Result:           result.ResultUnknown,
+			}},
+			RevocationMethod: result.RevocationMethodCRL,
+		}
+	}
+
+	var (
+		serverResults               = make([]*result.ServerResult, 0, len(cert.CRLDistributionPoints))
+		lastErr                     error
+		crlURL                      string
+		hasFreshestCRLInCertificate = x509util.FindExtensionByOID(cert.Extensions, oidFreshestCRL) != nil
+	)
+
+	// The CRLDistributionPoints contains the URIs of all the CRL distribution
+	// points. Since it does not distinguish the reason field, it needs to check
+	// all the URIs to avoid missing any partial CRLs.
+	//
+	// For the majority of the certificates, there is only one CRL distribution
+	// point with one CRL URI, which will be cached, so checking all the URIs is
+	// not a performance issue.
+	for _, crlURL = range cert.CRLDistributionPoints {
+		bundle, err := opts.Fetcher.Fetch(ctx, crlURL)
+		if err != nil {
+			lastErr = fmt.Errorf("failed to download CRL from %s: %w", crlURL, err)
+			break
+		}
+
+		if hasFreshestCRLInCertificate && bundle.DeltaCRL == nil {
+			// | deltaCRL URL in cert | deltaCRL URL in baseCRL | support it? |
+			// |----------------------|-------------------------|-------------|
+			// | True                 | True                    | Yes         |
+			// | True                 | False                   | No          |
+			// | False                | True                    | Yes         |
+			// | False                | False                   | Yes         |
+			//
+			// if only the certificate has the freshest CRL, the bundle.DeltaCRL
+			// should be nil. We don't support this case now because the delta
+			// CRLs may have different scopes, but the Go built-in function
+			// skips the scope of the base CRL when parsing the certificate.
+			lastErr = errors.New("freshest CRL from certificate extension is not supported")
+			break
+		}
+
+		if err = validate(bundle, issuer); err != nil {
+			lastErr = fmt.Errorf("failed to validate CRL from %s: %w", crlURL, err)
+			break
+		}
+
+		crlResult, err := checkRevocation(cert, bundle, opts.SigningTime, crlURL)
+		if err != nil {
+			lastErr = fmt.Errorf("failed to check revocation status from %s: %w", crlURL, err)
+			break
+		}
+
+		if crlResult.Result == result.ResultRevoked {
+			return &result.CertRevocationResult{
+				Result:           result.ResultRevoked,
+				ServerResults:    []*result.ServerResult{crlResult},
+				RevocationMethod: result.RevocationMethodCRL,
+			}
+		}
+
+		serverResults = append(serverResults, crlResult)
+	}
+
+	if lastErr != nil {
+		return &result.CertRevocationResult{
+			Result: result.ResultUnknown,
+			ServerResults: []*result.ServerResult{
+				{
+					Result:           result.ResultUnknown,
+					Server:           crlURL,
+					Error:            lastErr,
+					RevocationMethod: result.RevocationMethodCRL,
+				}},
+			RevocationMethod: result.RevocationMethodCRL,
+		}
+	}
+
+	return &result.CertRevocationResult{
+		Result:           result.ResultOK,
+		ServerResults:    serverResults,
+		RevocationMethod: result.RevocationMethodCRL,
+	}
+}
+
+// Supported checks if the certificate supports CRL.
+func Supported(cert *x509.Certificate) bool {
+	return cert != nil && len(cert.CRLDistributionPoints) > 0
+}
+
+func validate(bundle *crl.Bundle, issuer *x509.Certificate) error {
+	// validate base CRL
+	baseCRL := bundle.BaseCRL
+	if err := validateCRL(baseCRL, issuer); err != nil {
+		return fmt.Errorf("failed to validate base CRL: %w", err)
+	}
+
+	if bundle.DeltaCRL == nil {
+		return nil
+	}
+
+	// validate delta CRL
+	// RFC 5280, Section 5.2.4
+	deltaCRL := bundle.DeltaCRL
+	if err := validateCRL(deltaCRL, issuer); err != nil {
+		return fmt.Errorf("failed to validate delta CRL: %w", err)
+	}
+	if deltaCRL.Number.Cmp(baseCRL.Number) <= 0 {
+		return fmt.Errorf("delta CRL number %d is not greater than the base CRL number %d", deltaCRL.Number, baseCRL.Number)
+	}
+
+	// check delta CRL indicator extension
+	extension := x509util.FindExtensionByOID(deltaCRL.Extensions, oidDeltaCRLIndicator)
+	if extension == nil {
+		return errors.New("delta CRL indicator extension is not found")
+	}
+	minimumBaseCRLNumber := new(big.Int)
+	value := cryptobyte.String(extension.Value)
+	if !value.ReadASN1Integer(minimumBaseCRLNumber) {
+		return errors.New("failed to parse delta CRL indicator extension")
+	}
+	if minimumBaseCRLNumber.Cmp(baseCRL.Number) > 0 {
+		return fmt.Errorf("delta CRL indicator %d is not less than or equal to the base CRL number %d", minimumBaseCRLNumber, baseCRL.Number)
+	}
+	return nil
+}
+
+func validateCRL(crl *x509.RevocationList, issuer *x509.Certificate) error {
+	// check signature
+	if err := crl.CheckSignatureFrom(issuer); err != nil {
+		return fmt.Errorf("CRL is not signed by CA %s: %w,", issuer.Subject, err)
+	}
+
+	// check validity
+	if crl.NextUpdate.IsZero() {
+		return errors.New("CRL NextUpdate is not set")
+	}
+	now := time.Now()
+	if now.After(crl.NextUpdate) {
+		return fmt.Errorf("expired CRL. Current time %v is after CRL NextUpdate %v", now, crl.NextUpdate)
+	}
+
+	for _, ext := range crl.Extensions {
+		switch {
+		case ext.Id.Equal(oidIssuingDistributionPoint):
+			// IssuingDistributionPoint is a critical extension that identifies
+			// the scope of the CRL. Since we will check all the CRL
+			// distribution points, it is not necessary to check this extension.
+		case ext.Id.Equal(oidDeltaCRLIndicator):
+			// will be checked in validate()
+		default:
+			if ext.Critical {
+				// unsupported critical extensions is not allowed. (See RFC 5280, Section 5.2)
+				return fmt.Errorf("unsupported critical extension found in CRL: %v", ext.Id)
+			}
+		}
+	}
+
+	return nil
+}
+
+// checkRevocation checks if the certificate is revoked or not
+func checkRevocation(cert *x509.Certificate, b *crl.Bundle, signingTime time.Time, crlURL string) (*result.ServerResult, error) {
+	if cert == nil {
+		return nil, errors.New("certificate cannot be nil")
+	}
+	if b == nil {
+		return nil, errors.New("CRL bundle cannot be nil")
+	}
+	if b.BaseCRL == nil {
+		return nil, errors.New("baseCRL cannot be nil")
+	}
+
+	// merge the base and delta CRLs in a single iterator
+	revocationListIter := func(yield func(*x509.RevocationListEntry) bool) {
+		for i := range b.BaseCRL.RevokedCertificateEntries {
+			if !yield(&b.BaseCRL.RevokedCertificateEntries[i]) {
+				return
+			}
+		}
+		if b.DeltaCRL != nil {
+			for i := range b.DeltaCRL.RevokedCertificateEntries {
+				if !yield(&b.DeltaCRL.RevokedCertificateEntries[i]) {
+					return
+				}
+			}
+		}
+	}
+
+	// latestTempRevokedEntry contains the most recent revocation entry with
+	// reasons such as CertificateHold or RemoveFromCRL.
+	//
+	// If the certificate is revoked with CertificateHold, it is temporarily
+	// revoked. If the certificate is shown in the CRL with RemoveFromCRL,
+	// it is unrevoked.
+	var latestTempRevokedEntry *x509.RevocationListEntry
+
+	// iterate over all the entries in the base and delta CRLs
+	for revocationEntry := range revocationListIter {
+		if revocationEntry.SerialNumber.Cmp(cert.SerialNumber) == 0 {
+			extensions, err := parseEntryExtensions(revocationEntry)
+			if err != nil {
+				return nil, err
+			}
+
+			// validate signingTime and invalidityDate
+			if !signingTime.IsZero() && !extensions.invalidityDate.IsZero() &&
+				signingTime.Before(extensions.invalidityDate) {
+				// signing time is before the invalidity date which means the
+				// certificate is not revoked at the time of signing.
+				return &result.ServerResult{
+					Result:           result.ResultOK,
+					Server:           crlURL,
+					RevocationMethod: result.RevocationMethodCRL,
+				}, nil
+			}
+
+			switch revocationEntry.ReasonCode {
+			case reasonCodeCertificateHold, reasonCodeRemoveFromCRL:
+				// temporarily revoked or unrevoked
+				if latestTempRevokedEntry == nil || latestTempRevokedEntry.RevocationTime.Before(revocationEntry.RevocationTime) {
+					// the revocation status depends on the most recent reason
+					latestTempRevokedEntry = revocationEntry
+				}
+			default:
+				// permanently revoked
+				return &result.ServerResult{
+					Result:           result.ResultRevoked,
+					Server:           crlURL,
+					RevocationMethod: result.RevocationMethodCRL,
+				}, nil
+			}
+		}
+	}
+	if latestTempRevokedEntry != nil && latestTempRevokedEntry.ReasonCode == reasonCodeCertificateHold {
+		// revoked with CertificateHold
+		return &result.ServerResult{
+			Result:           result.ResultRevoked,
+			Server:           crlURL,
+			RevocationMethod: result.RevocationMethodCRL,
+		}, nil
+	}
+
+	return &result.ServerResult{
+		Result:           result.ResultOK,
+		Server:           crlURL,
+		RevocationMethod: result.RevocationMethodCRL,
+	}, nil
+}
+
+type entryExtensions struct {
+	// invalidityDate is the date when the key is invalid.
+	invalidityDate time.Time
+}
+
+func parseEntryExtensions(entry *x509.RevocationListEntry) (entryExtensions, error) {
+	var extensions entryExtensions
+	for _, ext := range entry.Extensions {
+		switch {
+		case ext.Id.Equal(oidInvalidityDate):
+			var invalidityDate time.Time
+			rest, err := asn1.UnmarshalWithParams(ext.Value, &invalidityDate, "generalized")
+			if err != nil {
+				return entryExtensions{}, fmt.Errorf("failed to parse invalidity date: %w", err)
+			}
+			if len(rest) > 0 {
+				return entryExtensions{}, fmt.Errorf("invalid invalidity date extension: trailing data")
+			}
+
+			extensions.invalidityDate = invalidityDate
+		default:
+			if ext.Critical {
+				// unsupported critical extensions is not allowed. (See RFC 5280, Section 5.2)
+				return entryExtensions{}, fmt.Errorf("unsupported critical extension found in CRL: %v", ext.Id)
+			}
+		}
+	}
+
+	return extensions, nil
+}

revocation/internal/ocsp/errors.go

@@ -0,0 +1,68 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package ocsp provides methods for checking the OCSP revocation status of a
+// certificate chain, as well as errors related to these checks
+package ocsp
+
+import (
+	"fmt"
+	"time"
+)
+
+// RevokedError is returned when the certificate's status for OCSP is
+// ocsp.Revoked
+type RevokedError struct{}
+
+func (e RevokedError) Error() string {
+	return "certificate is revoked via OCSP"
+}
+
+// UnknownStatusError is returned when the certificate's status for OCSP is
+// ocsp.Unknown
+type UnknownStatusError struct{}
+
+func (e UnknownStatusError) Error() string {
+	return "certificate has unknown status via OCSP"
+}
+
+// GenericError is returned when there is an error during the OCSP revocation
+// check, not necessarily a revocation
+type GenericError struct {
+	Err error
+}
+
+func (e GenericError) Error() string {
+	msg := "error checking revocation status via OCSP"
+	if e.Err != nil {
+		return fmt.Sprintf("%s: %v", msg, e.Err)
+	}
+	return msg
+}
+
+// NoServerError is returned when the OCSPServer is not specified.
+type NoServerError struct{}
+
+func (e NoServerError) Error() string {
+	return "no valid OCSP server found"
+}
+
+// TimeoutError is returned when the connection attempt to an OCSP URL exceeds
+// the specified threshold
+type TimeoutError struct {
+	timeout time.Duration
+}
+
+func (e TimeoutError) Error() string {
+	return fmt.Sprintf("exceeded timeout threshold of %.2f seconds for OCSP check", e.timeout.Seconds())
+}

revocation/internal/ocsp/ocsp.go

@@ -0,0 +1,254 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package ocsp provides methods for checking the OCSP revocation status of a
+// certificate chain, as well as errors related to these checks
+package ocsp
+
+import (
+	"bytes"
+	"context"
+	"crypto"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/asn1"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+
+	"github.com/notaryproject/notation-core-go/revocation/result"
+	"golang.org/x/crypto/ocsp"
+)
+
+// CertCheckStatusOptions specifies values that are needed to check OCSP revocation
+type CertCheckStatusOptions struct {
+	// HTTPClient is the HTTP client used to perform the OCSP request
+	HTTPClient *http.Client
+
+	// SigningTime is used to compare with the invalidity date during revocation
+	SigningTime time.Time
+}
+
+const (
+	pkixNoCheckOID    string = "1.3.6.1.5.5.7.48.1.5"
+	invalidityDateOID string = "2.5.29.24"
+	// Max size determined from https://www.ibm.com/docs/en/sva/9.0.6?topic=stanza-ocsp-max-response-size.
+	// Typical size is ~4 KB
+	ocspMaxResponseSize int64 = 20480 //bytes
+)
+
+// CertCheckStatus checks the revocation status of a certificate using OCSP
+func CertCheckStatus(ctx context.Context, cert, issuer *x509.Certificate, opts CertCheckStatusOptions) *result.CertRevocationResult {
+	if !Supported(cert) {
+		// OCSP not enabled for this certificate.
+		return &result.CertRevocationResult{
+			Result:           result.ResultNonRevokable,
+			ServerResults:    []*result.ServerResult{toServerResult("", NoServerError{})},
+			RevocationMethod: result.RevocationMethodOCSP,
+		}
+	}
+	ocspURLs := cert.OCSPServer
+
+	serverResults := make([]*result.ServerResult, len(ocspURLs))
+	for serverIndex, server := range ocspURLs {
+		serverResult := checkStatusFromServer(ctx, cert, issuer, server, opts)
+		if serverResult.Result == result.ResultOK ||
+			serverResult.Result == result.ResultRevoked ||
+			(serverResult.Result == result.ResultUnknown && errors.Is(serverResult.Error, UnknownStatusError{})) {
+			// A valid response has been received from an OCSP server
+			// Result should be based on only this response, not any errors from
+			// other servers
+			return serverResultsToCertRevocationResult([]*result.ServerResult{serverResult})
+		}
+		serverResults[serverIndex] = serverResult
+	}
+	return serverResultsToCertRevocationResult(serverResults)
+}
+
+// Supported returns true if the certificate supports OCSP.
+func Supported(cert *x509.Certificate) bool {
+	return cert != nil && len(cert.OCSPServer) > 0
+}
+
+func checkStatusFromServer(ctx context.Context, cert, issuer *x509.Certificate, server string, opts CertCheckStatusOptions) *result.ServerResult {
+	// Check valid server
+	if serverURL, err := url.Parse(server); err != nil || !strings.EqualFold(serverURL.Scheme, "http") {
+		// This function is only able to check servers that are accessible via HTTP
+		return toServerResult(server, GenericError{Err: fmt.Errorf("OCSPServer protocol %s is not supported", serverURL.Scheme)})
+	}
+
+	// Create OCSP Request
+	resp, err := executeOCSPCheck(ctx, cert, issuer, server, opts)
+	if err != nil {
+		// If there is a server error, attempt all servers before determining what to return
+		// to the user
+		return toServerResult(server, err)
+	}
+
+	// Validate OCSP response isn't expired
+	if time.Now().After(resp.NextUpdate) {
+		return toServerResult(server, GenericError{Err: errors.New("expired OCSP response")})
+	}
+
+	// Handle pkix-ocsp-no-check and id-ce-invalidityDate extensions if present
+	// in response
+	extensionMap := extensionsToMap(resp.Extensions)
+	if _, foundNoCheck := extensionMap[pkixNoCheckOID]; !foundNoCheck {
+		// This will be ignored until CRL is implemented
+		// If it isn't found, CRL should be used to verify the OCSP response
+		_ = foundNoCheck // needed to bypass linter warnings (Remove after adding CRL)
+		// TODO: add CRL support
+		// https://github.com/notaryproject/notation-core-go/issues/125
+	}
+	if invalidityDateBytes, foundInvalidityDate := extensionMap[invalidityDateOID]; foundInvalidityDate && !opts.SigningTime.IsZero() && resp.Status == ocsp.Revoked {
+		var invalidityDate time.Time
+		rest, err := asn1.UnmarshalWithParams(invalidityDateBytes, &invalidityDate, "generalized")
+		if len(rest) == 0 && err == nil && opts.SigningTime.Before(invalidityDate) {
+			return toServerResult(server, nil)
+		}
+	}
+
+	// No errors, valid server response
+	switch resp.Status {
+	case ocsp.Good:
+		return toServerResult(server, nil)
+	case ocsp.Revoked:
+		return toServerResult(server, RevokedError{})
+	default:
+		// ocsp.Unknown
+		return toServerResult(server, UnknownStatusError{})
+	}
+}
+
+func extensionsToMap(extensions []pkix.Extension) map[string][]byte {
+	extensionMap := make(map[string][]byte)
+	for _, extension := range extensions {
+		extensionMap[extension.Id.String()] = extension.Value
+	}
+	return extensionMap
+}
+
+func executeOCSPCheck(ctx context.Context, cert, issuer *x509.Certificate, server string, opts CertCheckStatusOptions) (*ocsp.Response, error) {
+	// TODO: Look into other alternatives for specifying the Hash
+	// https://github.com/notaryproject/notation-core-go/issues/139
+	// The following do not support SHA256 hashes:
+	//  - Microsoft
+	//  - Entrust
+	//  - Let's Encrypt
+	//  - Digicert (sometimes)
+	// As this represents a large percentage of public CAs, we are using the
+	// hashing algorithm SHA1, which has been confirmed to be supported by all
+	// that were tested.
+	ocspRequest, err := ocsp.CreateRequest(cert, issuer, &ocsp.RequestOptions{Hash: crypto.SHA1})
+	if err != nil {
+		return nil, GenericError{Err: err}
+	}
+
+	var resp *http.Response
+	postRequired := base64.StdEncoding.EncodedLen(len(ocspRequest)) >= 255
+	if !postRequired {
+		encodedReq := url.QueryEscape(base64.StdEncoding.EncodeToString(ocspRequest))
+		if len(encodedReq) < 255 {
+			var reqURL string
+			reqURL, err = url.JoinPath(server, encodedReq)
+			if err != nil {
+				return nil, GenericError{Err: err}
+			}
+			var httpReq *http.Request
+			httpReq, err = http.NewRequestWithContext(ctx, http.MethodGet, reqURL, nil)
+			if err != nil {
+				return nil, err
+			}
+			resp, err = opts.HTTPClient.Do(httpReq)
+		} else {
+			resp, err = postRequest(ctx, ocspRequest, server, opts.HTTPClient)
+		}
+	} else {
+		resp, err = postRequest(ctx, ocspRequest, server, opts.HTTPClient)
+	}
+
+	if err != nil {
+		var urlErr *url.Error
+		if errors.As(err, &urlErr) && urlErr.Timeout() {
+			return nil, TimeoutError{
+				timeout: opts.HTTPClient.Timeout,
+			}
+		}
+		return nil, GenericError{Err: err}
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("failed to retrieve OCSP: response had status code %d", resp.StatusCode)
+	}
+
+	body, err := io.ReadAll(io.LimitReader(resp.Body, ocspMaxResponseSize))
+	if err != nil {
+		return nil, GenericError{Err: err}
+	}
+
+	switch {
+	case bytes.Equal(body, ocsp.UnauthorizedErrorResponse):
+		return nil, GenericError{Err: errors.New("OCSP unauthorized")}
+	case bytes.Equal(body, ocsp.MalformedRequestErrorResponse):
+		return nil, GenericError{Err: errors.New("OCSP malformed")}
+	case bytes.Equal(body, ocsp.InternalErrorErrorResponse):
+		return nil, GenericError{Err: errors.New("OCSP internal error")}
+	case bytes.Equal(body, ocsp.TryLaterErrorResponse):
+		return nil, GenericError{Err: errors.New("OCSP try later")}
+	case bytes.Equal(body, ocsp.SigRequredErrorResponse):
+		return nil, GenericError{Err: errors.New("OCSP signature required")}
+	}
+
+	return ocsp.ParseResponseForCert(body, cert, issuer)
+}
+
+func postRequest(ctx context.Context, req []byte, server string, httpClient *http.Client) (*http.Response, error) {
+	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, server, bytes.NewReader(req))
+	if err != nil {
+		return nil, err
+	}
+	httpReq.Header.Set("Content-Type", "application/ocsp-request")
+	return httpClient.Do(httpReq)
+}
+
+func toServerResult(server string, err error) *result.ServerResult {
+	var serverResult *result.ServerResult
+	switch t := err.(type) {
+	case nil:
+		serverResult = result.NewServerResult(result.ResultOK, server, nil)
+	case NoServerError:
+		serverResult = result.NewServerResult(result.ResultNonRevokable, server, nil)
+	case RevokedError:
+		serverResult = result.NewServerResult(result.ResultRevoked, server, t)
+	default:
+		// Includes GenericError, UnknownStatusError, result.InvalidChainError,
+		// and TimeoutError
+		serverResult = result.NewServerResult(result.ResultUnknown, server, t)
+	}
+	serverResult.RevocationMethod = result.RevocationMethodOCSP
+	return serverResult
+}
+
+func serverResultsToCertRevocationResult(serverResults []*result.ServerResult) *result.CertRevocationResult {
+	return &result.CertRevocationResult{
+		Result:           serverResults[len(serverResults)-1].Result,
+		ServerResults:    serverResults,
+		RevocationMethod: result.RevocationMethodOCSP,
+	}
+}

revocation/internal/ocsp/ocsp_test.go

@@ -0,0 +1,296 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package ocsp
+
+import (
+	"context"
+	"crypto/x509"
+	"fmt"
+	"net/http"
+	"net/url"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/notaryproject/notation-core-go/revocation/result"
+	"github.com/notaryproject/notation-core-go/testhelper"
+	"golang.org/x/crypto/ocsp"
+)
+
+func validateEquivalentCertResults(certResults, expectedCertResults []*result.CertRevocationResult, t *testing.T) {
+	if len(certResults) != len(expectedCertResults) {
+		t.Errorf("Length of certResults (%d) did not match expected length (%d)", len(certResults), len(expectedCertResults))
+		return
+	}
+	for i, certResult := range certResults {
+		if certResult.Result != expectedCertResults[i].Result {
+			t.Errorf("Expected certResults[%d].Result to be %s, but got %s", i, expectedCertResults[i].Result, certResult.Result)
+		}
+		if len(certResult.ServerResults) != len(expectedCertResults[i].ServerResults) {
+			t.Errorf("Length of certResults[%d].ServerResults (%d) did not match expected length (%d)", i, len(certResult.ServerResults), len(expectedCertResults[i].ServerResults))
+			return
+		}
+		for j, serverResult := range certResult.ServerResults {
+			if serverResult.Result != expectedCertResults[i].ServerResults[j].Result {
+				t.Errorf("Expected certResults[%d].ServerResults[%d].Result to be %s, but got %s", i, j, expectedCertResults[i].ServerResults[j].Result, serverResult.Result)
+			}
+			if serverResult.Server != expectedCertResults[i].ServerResults[j].Server {
+				t.Errorf("Expected certResults[%d].ServerResults[%d].Server to be %s, but got %s", i, j, expectedCertResults[i].ServerResults[j].Server, serverResult.Server)
+			}
+			if serverResult.Error == nil {
+				if expectedCertResults[i].ServerResults[j].Error == nil {
+					continue
+				}
+				t.Errorf("certResults[%d].ServerResults[%d].Error was nil, but expected %v", i, j, expectedCertResults[i].ServerResults[j].Error)
+			} else if expectedCertResults[i].ServerResults[j].Error == nil {
+				t.Errorf("Unexpected error for certResults[%d].ServerResults[%d].Error: %v", i, j, serverResult.Error)
+			} else if serverResult.Error.Error() != expectedCertResults[i].ServerResults[j].Error.Error() {
+				t.Errorf("Expected certResults[%d].ServerResults[%d].Error to be %v, but got %v", i, j, expectedCertResults[i].ServerResults[j].Error, serverResult.Error)
+			}
+		}
+	}
+}
+
+func getOKCertResult(server string) *result.CertRevocationResult {
+	return &result.CertRevocationResult{
+		Result: result.ResultOK,
+		ServerResults: []*result.ServerResult{
+			result.NewServerResult(result.ResultOK, server, nil),
+		},
+	}
+}
+
+func TestCheckStatus(t *testing.T) {
+	revokableCertTuple := testhelper.GetRevokableRSALeafCertificate()
+	revokableIssuerTuple := testhelper.GetRSARootCertificate()
+	ocspServer := revokableCertTuple.Cert.OCSPServer[0]
+	revokableChain := []*x509.Certificate{revokableCertTuple.Cert, revokableIssuerTuple.Cert}
+	testChain := []testhelper.RSACertTuple{revokableCertTuple, revokableIssuerTuple}
+	ctx := context.Background()
+
+	t.Run("check non-revoked cert", func(t *testing.T) {
+		client := testhelper.MockClient(testChain, []ocsp.ResponseStatus{ocsp.Good}, nil, true)
+		opts := CertCheckStatusOptions{
+			SigningTime: time.Now(),
+			HTTPClient:  client,
+		}
+
+		certResult := CertCheckStatus(ctx, revokableChain[0], revokableChain[1], opts)
+		expectedCertResults := []*result.CertRevocationResult{getOKCertResult(ocspServer)}
+		validateEquivalentCertResults([]*result.CertRevocationResult{certResult}, expectedCertResults, t)
+	})
+	t.Run("check cert with Unknown OCSP response", func(t *testing.T) {
+		client := testhelper.MockClient(testChain, []ocsp.ResponseStatus{ocsp.Unknown}, nil, true)
+		opts := CertCheckStatusOptions{
+			SigningTime: time.Now(),
+			HTTPClient:  client,
+		}
+
+		certResult := CertCheckStatus(ctx, revokableChain[0], revokableChain[1], opts)
+		expectedCertResults := []*result.CertRevocationResult{{
+			Result: result.ResultUnknown,
+			ServerResults: []*result.ServerResult{
+				result.NewServerResult(result.ResultUnknown, ocspServer, UnknownStatusError{}),
+			},
+		}}
+		validateEquivalentCertResults([]*result.CertRevocationResult{certResult}, expectedCertResults, t)
+	})
+	t.Run("check OCSP revoked cert", func(t *testing.T) {
+		client := testhelper.MockClient(testChain, []ocsp.ResponseStatus{ocsp.Revoked}, nil, true)
+		opts := CertCheckStatusOptions{
+			SigningTime: time.Now(),
+			HTTPClient:  client,
+		}
+
+		certResult := CertCheckStatus(ctx, revokableChain[0], revokableChain[1], opts)
+		expectedCertResults := []*result.CertRevocationResult{{
+			Result: result.ResultRevoked,
+			ServerResults: []*result.ServerResult{
+				result.NewServerResult(result.ResultRevoked, ocspServer, RevokedError{}),
+			},
+		}}
+		validateEquivalentCertResults([]*result.CertRevocationResult{certResult}, expectedCertResults, t)
+	})
+	t.Run("check OCSP future revoked cert", func(t *testing.T) {
+		revokedTime := time.Now().Add(time.Hour)
+		client := testhelper.MockClient(testChain, []ocsp.ResponseStatus{ocsp.Revoked}, &revokedTime, true)
+		opts := CertCheckStatusOptions{
+			SigningTime: time.Now(),
+			HTTPClient:  client,
+		}
+
+		certResult := CertCheckStatus(ctx, revokableChain[0], revokableChain[1], opts)
+		expectedCertResults := []*result.CertRevocationResult{getOKCertResult(ocspServer)}
+		validateEquivalentCertResults([]*result.CertRevocationResult{certResult}, expectedCertResults, t)
+	})
+
+	t.Run("certificate doesn't support OCSP", func(t *testing.T) {
+		ocspResult := CertCheckStatus(ctx, &x509.Certificate{}, revokableIssuerTuple.Cert, CertCheckStatusOptions{})
+		expectedResult := &result.CertRevocationResult{
+			Result:        result.ResultNonRevokable,
+			ServerResults: []*result.ServerResult{toServerResult("", NoServerError{})},
+		}
+
+		validateEquivalentCertResults([]*result.CertRevocationResult{ocspResult}, []*result.CertRevocationResult{expectedResult}, t)
+	})
+}
+
+func TestCheckStatusFromServer(t *testing.T) {
+	revokableCertTuple := testhelper.GetRevokableRSALeafCertificate()
+	revokableIssuerTuple := testhelper.GetRSARootCertificate()
+	ctx := context.Background()
+
+	t.Run("server url is not http", func(t *testing.T) {
+		server := "https://localhost.test"
+		serverResult := checkStatusFromServer(ctx, revokableCertTuple.Cert, revokableIssuerTuple.Cert, server, CertCheckStatusOptions{})
+		expectedResult := toServerResult(server, GenericError{Err: fmt.Errorf("OCSPServer protocol %s is not supported", "https")})
+		if serverResult.Result != expectedResult.Result {
+			t.Errorf("Expected Result to be %s, but got %s", expectedResult.Result, serverResult.Result)
+		}
+		if serverResult.Server != expectedResult.Server {
+			t.Errorf("Expected Server to be %s, but got %s", expectedResult.Server, serverResult.Server)
+		}
+		if serverResult.Error == nil {
+			t.Errorf("Expected Error to be %v, but got nil", expectedResult.Error)
+		} else if serverResult.Error.Error() != expectedResult.Error.Error() {
+			t.Errorf("Expected Error to be %v, but got %v", expectedResult.Error, serverResult.Error)
+		}
+	})
+
+	t.Run("request error", func(t *testing.T) {
+		server := "http://localhost.test"
+		serverResult := checkStatusFromServer(ctx, revokableCertTuple.Cert, revokableIssuerTuple.Cert, server, CertCheckStatusOptions{
+			HTTPClient: &http.Client{
+				Transport: &failedTransport{},
+			},
+		})
+		errorMessage := "failed to execute request"
+		if !strings.Contains(serverResult.Error.Error(), errorMessage) {
+			t.Errorf("Expected Error to contain %v, but got %v", errorMessage, serverResult.Error)
+		}
+	})
+
+	t.Run("ocsp expired", func(t *testing.T) {
+		client := testhelper.MockClient([]testhelper.RSACertTuple{revokableCertTuple, revokableIssuerTuple}, []ocsp.ResponseStatus{ocsp.Good}, nil, true)
+		server := "http://localhost.test/expired_ocsp"
+		serverResult := checkStatusFromServer(ctx, revokableCertTuple.Cert, revokableIssuerTuple.Cert, server, CertCheckStatusOptions{
+			HTTPClient: client,
+		})
+		errorMessage := "expired OCSP response"
+		if !strings.Contains(serverResult.Error.Error(), errorMessage) {
+			t.Errorf("Expected Error to contain %v, but got %v", errorMessage, serverResult.Error)
+		}
+	})
+
+	t.Run("ocsp request roundtrip failed", func(t *testing.T) {
+		client := testhelper.MockClient([]testhelper.RSACertTuple{revokableCertTuple, revokableIssuerTuple}, []ocsp.ResponseStatus{ocsp.Good}, nil, true)
+		server := "http://localhost.test"
+		serverResult := checkStatusFromServer(nil, revokableCertTuple.Cert, revokableIssuerTuple.Cert, server, CertCheckStatusOptions{
+			HTTPClient: client,
+		})
+		errorMessage := "net/http: nil Context"
+		if !strings.Contains(serverResult.Error.Error(), errorMessage) {
+			t.Errorf("Expected Error to contain %v, but got %v", errorMessage, serverResult.Error)
+		}
+	})
+
+	t.Run("ocsp request roundtrip timeout", func(t *testing.T) {
+		server := "http://localhost.test"
+		serverResult := checkStatusFromServer(ctx, revokableCertTuple.Cert, revokableIssuerTuple.Cert, server, CertCheckStatusOptions{
+			HTTPClient: &http.Client{
+				Timeout: 1 * time.Second,
+				Transport: &failedTransport{
+					timeout: true,
+				},
+			},
+		})
+		errorMessage := "exceeded timeout threshold of 1.00 seconds for OCSP check"
+		if !strings.Contains(serverResult.Error.Error(), errorMessage) {
+			t.Errorf("Expected Error to contain %v, but got %v", errorMessage, serverResult.Error)
+		}
+	})
+}
+
+func TestPostRequest(t *testing.T) {
+	t.Run("failed to generate request", func(t *testing.T) {
+		_, err := postRequest(nil, nil, "http://localhost.test", &http.Client{
+			Transport: &failedTransport{},
+		})
+		expectedErrMsg := "net/http: nil Context"
+		if err == nil || err.Error() != expectedErrMsg {
+			t.Errorf("Expected error %s, but got %s", expectedErrMsg, err)
+		}
+	})
+
+	t.Run("failed to execute request", func(t *testing.T) {
+		_, err := postRequest(context.Background(), nil, "http://localhost.test", &http.Client{
+			Transport: &failedTransport{},
+		})
+		expectedErrMsg := "Post \"http://localhost.test\": failed to execute request"
+		if err == nil || err.Error() != expectedErrMsg {
+			t.Errorf("Expected error %s, but got %s", expectedErrMsg, err)
+		}
+	})
+}
+
+func TestExecuteOCSPCheck(t *testing.T) {
+	revokableCertTuple := testhelper.GetRevokableRSALeafCertificate()
+	revokableIssuerTuple := testhelper.GetRSARootCertificate()
+	ctx := context.Background()
+
+	t.Run("http response status is not 200", func(t *testing.T) {
+		_, err := executeOCSPCheck(ctx, revokableCertTuple.Cert, revokableIssuerTuple.Cert, "localhost.test", CertCheckStatusOptions{
+			HTTPClient: &http.Client{
+				Transport: &failedTransport{
+					statusCode: http.StatusNotFound,
+				},
+			},
+		})
+		expectedErrMsg := "failed to retrieve OCSP: response had status code 404"
+		if err == nil || err.Error() != expectedErrMsg {
+			t.Errorf("Expected error %s, but got %s", expectedErrMsg, err)
+		}
+	})
+}
+
+type testTimeoutError struct{}
+
+func (e testTimeoutError) Error() string {
+	return "test timeout"
+}
+
+func (e testTimeoutError) Timeout() bool {
+	return true
+}
+
+type failedTransport struct {
+	timeout    bool
+	statusCode int
+}
+
+func (f *failedTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	if f.timeout {
+		return nil, &url.Error{
+			Err: testTimeoutError{},
+		}
+	}
+
+	if f.statusCode != 0 {
+		return &http.Response{
+			StatusCode: f.statusCode,
+		}, nil
+	}
+
+	return nil, fmt.Errorf("failed to execute request")
+}

revocation/internal/x509util/extension.go

@@ -0,0 +1,31 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package x509util
+
+import (
+	"crypto/x509/pkix"
+	"encoding/asn1"
+	"slices"
+)
+
+// FindExtensionByOID finds the extension by the given OID.
+func FindExtensionByOID(extensions []pkix.Extension, oid asn1.ObjectIdentifier) *pkix.Extension {
+	idx := slices.IndexFunc(extensions, func(ext pkix.Extension) bool {
+		return ext.Id.Equal(oid)
+	})
+	if idx < 0 {
+		return nil
+	}
+	return &extensions[idx]
+}

revocation/internal/x509util/extension_test.go

@@ -0,0 +1,58 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package x509util
+
+import (
+	"crypto/x509/pkix"
+	"encoding/asn1"
+	"testing"
+)
+
+func TestFindExtensionByOID(t *testing.T) {
+	oid1 := asn1.ObjectIdentifier{1, 2, 3, 4}
+	oid2 := asn1.ObjectIdentifier{1, 2, 3, 5}
+	extensions := []pkix.Extension{
+		{Id: oid1, Value: []byte("value1")},
+		{Id: oid2, Value: []byte("value2")},
+	}
+
+	tests := []struct {
+		name       string
+		oid        asn1.ObjectIdentifier
+		extensions []pkix.Extension
+		expected   *pkix.Extension
+	}{
+		{
+			name:       "Extension found",
+			oid:        oid1,
+			extensions: extensions,
+			expected:   &extensions[0],
+		},
+		{
+			name:       "Extension not found",
+			oid:        asn1.ObjectIdentifier{1, 2, 3, 6},
+			extensions: extensions,
+			expected:   nil,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := FindExtensionByOID(tt.extensions, tt.oid)
+			if result != tt.expected {
+				t.Errorf("expected %v, got %v", tt.expected, result)
+			}
+		})
+	}
+}

revocation/internal/x509util/validate.go

@@ -0,0 +1,48 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package x509util provides the method to validate the certificate chain for a
+// specific purpose, including code signing and timestamping. It also provides
+// the method to find the extension by the given OID.
+package x509util
+
+import (
+	"crypto/x509"
+	"fmt"
+
+	"github.com/notaryproject/notation-core-go/revocation/purpose"
+	"github.com/notaryproject/notation-core-go/revocation/result"
+	coreX509 "github.com/notaryproject/notation-core-go/x509"
+)
+
+// ValidateChain checks the certificate chain for a specific purpose, including
+// code signing and timestamping.
+func ValidateChain(certChain []*x509.Certificate, certChainPurpose purpose.Purpose) error {
+	switch certChainPurpose {
+	case purpose.CodeSigning:
+		// Since ValidateCodeSigningCertChain is using authentic signing time,
+		// signing time may be zero.
+		// Thus, it is better to pass nil here than fail for a cert's NotBefore
+		// being after zero time
+		if err := coreX509.ValidateCodeSigningCertChain(certChain, nil); err != nil {
+			return result.InvalidChainError{Err: err}
+		}
+	case purpose.Timestamping:
+		if err := coreX509.ValidateTimestampingCertChain(certChain); err != nil {
+			return result.InvalidChainError{Err: err}
+		}
+	default:
+		return result.InvalidChainError{Err: fmt.Errorf("unsupported certificate chain purpose %v", certChainPurpose)}
+	}
+	return nil
+}

revocation/internal/x509util/validate_test.go

@@ -0,0 +1,60 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package x509util
+
+import (
+	"crypto/x509"
+	"testing"
+
+	"github.com/notaryproject/notation-core-go/revocation/purpose"
+	"github.com/notaryproject/notation-core-go/testhelper"
+)
+
+func TestValidate(t *testing.T) {
+	t.Run("unsupported_certificate_chain_purpose", func(t *testing.T) {
+		certChain := []*x509.Certificate{}
+		certChainPurpose := purpose.Purpose(-1)
+		err := ValidateChain(certChain, certChainPurpose)
+		if err == nil {
+			t.Errorf("Validate() failed, expected error, got nil")
+		}
+	})
+
+	t.Run("invalid code signing certificate chain", func(t *testing.T) {
+		certChain := []*x509.Certificate{}
+		certChainPurpose := purpose.CodeSigning
+		err := ValidateChain(certChain, certChainPurpose)
+		if err == nil {
+			t.Errorf("Validate() failed, expected error, got nil")
+		}
+	})
+
+	t.Run("invalid timestamping certificate chain", func(t *testing.T) {
+		certChain := []*x509.Certificate{}
+		certChainPurpose := purpose.Timestamping
+		err := ValidateChain(certChain, certChainPurpose)
+		if err == nil {
+			t.Errorf("Validate() failed, expected error, got nil")
+		}
+	})
+
+	t.Run("valid code signing certificate chain", func(t *testing.T) {
+		certChain := testhelper.GetRevokableRSAChain(2)
+		certChainPurpose := purpose.CodeSigning
+		err := ValidateChain([]*x509.Certificate{certChain[0].Cert, certChain[1].Cert}, certChainPurpose)
+		if err != nil {
+			t.Errorf("Validate() failed, expected nil, got %v", err)
+		}
+	})
+}

revocation/ocsp/errors.go

@@ -11,58 +11,27 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// Package ocsp provides methods for checking the OCSP revocation status of a
-// certificate chain, as well as errors related to these checks
 package ocsp
 
-import (
+import "github.com/notaryproject/notation-core-go/revocation/internal/ocsp"
-	"fmt"
+
-	"time"
+type (
+	// RevokedError is returned when the certificate's status for OCSP is
+	// ocsp.Revoked
+	RevokedError = ocsp.RevokedError
+
+	// UnknownStatusError is returned when the certificate's status for OCSP is
+	// ocsp.Unknown
+	UnknownStatusError = ocsp.UnknownStatusError
+
+	// GenericError is returned when there is an error during the OCSP revocation
+	// check, not necessarily a revocation
+	GenericError = ocsp.GenericError
+
+	// NoServerError is returned when the OCSPServer is not specified.
+	NoServerError = ocsp.NoServerError
+
+	// TimeoutError is returned when the connection attempt to an OCSP URL exceeds
+	// the specified threshold
+	TimeoutError = ocsp.TimeoutError
 )
-
-// RevokedError is returned when the certificate's status for OCSP is
-// ocsp.Revoked
-type RevokedError struct{}
-
-func (e RevokedError) Error() string {
-	return "certificate is revoked via OCSP"
-}
-
-// UnknownStatusError is returned when the certificate's status for OCSP is
-// ocsp.Unknown
-type UnknownStatusError struct{}
-
-func (e UnknownStatusError) Error() string {
-	return "certificate has unknown status via OCSP"
-}
-
-// GenericError is returned when there is an error during the OCSP revocation
-// check, not necessarily a revocation
-type GenericError struct {
-	Err error
-}
-
-func (e GenericError) Error() string {
-	msg := "error checking revocation status via OCSP"
-	if e.Err != nil {
-		return fmt.Sprintf("%s: %v", msg, e.Err)
-	}
-	return msg
-}
-
-// NoServerError is returned when the OCSPServer is not specified.
-type NoServerError struct{}
-
-func (e NoServerError) Error() string {
-	return "no valid OCSP server found"
-}
-
-// TimeoutError is returned when the connection attempt to an OCSP URL exceeds
-// the specified threshold
-type TimeoutError struct {
-	timeout time.Duration
-}
-
-func (e TimeoutError) Error() string {
-	return fmt.Sprintf("exceeded timeout threshold of %.2f seconds for OCSP check", e.timeout.Seconds())
-}

revocation/ocsp/ocsp.go

@@ -16,41 +16,31 @@
 package ocsp
 
 import (
-	"bytes"
+	"context"
-	"crypto"
 	"crypto/x509"
-	"crypto/x509/pkix"
-	"encoding/asn1"
-	"encoding/base64"
 	"errors"
-	"fmt"
-	"io"
 	"net/http"
-	"net/url"
-	"strings"
 	"sync"
 	"time"
 
+	"github.com/notaryproject/notation-core-go/revocation/internal/ocsp"
+	"github.com/notaryproject/notation-core-go/revocation/internal/x509util"
+	"github.com/notaryproject/notation-core-go/revocation/purpose"
 	"github.com/notaryproject/notation-core-go/revocation/result"
-	coreX509 "github.com/notaryproject/notation-core-go/x509"
-	"golang.org/x/crypto/ocsp"
 )
 
 // Options specifies values that are needed to check OCSP revocation
 type Options struct {
 	CertChain []*x509.Certificate
+
+	// CertChainPurpose is the purpose of the certificate chain. Supported
+	// values are CodeSigning and Timestamping.
+	// When not provided, the default value is CodeSigning.
+	CertChainPurpose purpose.Purpose
 	SigningTime      time.Time
 	HTTPClient       *http.Client
 }
 
-const (
-	pkixNoCheckOID    string = "1.3.6.1.5.5.7.48.1.5"
-	invalidityDateOID string = "2.5.29.24"
-	// Max size determined from https://www.ibm.com/docs/en/sva/9.0.6?topic=stanza-ocsp-max-response-size.
-	// Typical size is ~4 KB
-	ocspMaxResponseSize int64 = 20480 //bytes
-)
-
 // CheckStatus checks OCSP based on the passed options and returns an array of
 // result.CertRevocationResult objects that contains the results and error. The
 // length of this array will always be equal to the length of the certificate
@@ -60,24 +50,25 @@ func CheckStatus(opts Options) ([]*result.CertRevocationResult, error) {
 		return nil, result.InvalidChainError{Err: errors.New("chain does not contain any certificates")}
 	}
 
-	// Validate cert chain structure
+	if err := x509util.ValidateChain(opts.CertChain, opts.CertChainPurpose); err != nil {
-	// Since this is using authentic signing time, signing time may be zero.
+		return nil, err
-	// Thus, it is better to pass nil here than fail for a cert's NotBefore
-	// being after zero time
-	if err := coreX509.ValidateCodeSigningCertChain(opts.CertChain, nil); err != nil {
-		return nil, result.InvalidChainError{Err: err}
 	}
 
 	certResults := make([]*result.CertRevocationResult, len(opts.CertChain))
+	certCheckStatusOptions := ocsp.CertCheckStatusOptions{
+		SigningTime: opts.SigningTime,
+		HTTPClient:  opts.HTTPClient,
+	}
 
 	// Check status for each cert in cert chain
 	var wg sync.WaitGroup
+	ctx := context.Background()
 	for i, cert := range opts.CertChain[:len(opts.CertChain)-1] {
 		wg.Add(1)
 		// Assume cert chain is accurate and next cert in chain is the issuer
 		go func(i int, cert *x509.Certificate) {
 			defer wg.Done()
-			certResults[i] = certCheckStatus(cert, opts.CertChain[i+1], opts)
+			certResults[i] = ocsp.CertCheckStatus(ctx, cert, opts.CertChain[i+1], certCheckStatusOptions)
 		}(i, cert)
 	}
 	// Last is root cert, which will never be revoked by OCSP
@@ -92,182 +83,3 @@ func CheckStatus(opts Options) ([]*result.CertRevocationResult, error) {
 	wg.Wait()
 	return certResults, nil
 }
-
-func certCheckStatus(cert, issuer *x509.Certificate, opts Options) *result.CertRevocationResult {
-	ocspURLs := cert.OCSPServer
-	if len(ocspURLs) == 0 {
-		// OCSP not enabled for this certificate.
-		return &result.CertRevocationResult{
-			Result:        result.ResultNonRevokable,
-			ServerResults: []*result.ServerResult{toServerResult("", NoServerError{})},
-		}
-	}
-
-	serverResults := make([]*result.ServerResult, len(ocspURLs))
-	for serverIndex, server := range ocspURLs {
-		serverResult := checkStatusFromServer(cert, issuer, server, opts)
-		if serverResult.Result == result.ResultOK ||
-			serverResult.Result == result.ResultRevoked ||
-			(serverResult.Result == result.ResultUnknown && errors.Is(serverResult.Error, UnknownStatusError{})) {
-			// A valid response has been received from an OCSP server
-			// Result should be based on only this response, not any errors from
-			// other servers
-			return serverResultsToCertRevocationResult([]*result.ServerResult{serverResult})
-		}
-		serverResults[serverIndex] = serverResult
-	}
-	return serverResultsToCertRevocationResult(serverResults)
-}
-
-func checkStatusFromServer(cert, issuer *x509.Certificate, server string, opts Options) *result.ServerResult {
-	// Check valid server
-	if serverURL, err := url.Parse(server); err != nil || !strings.EqualFold(serverURL.Scheme, "http") {
-		// This function is only able to check servers that are accessible via HTTP
-		return toServerResult(server, GenericError{Err: fmt.Errorf("OCSPServer protocol %s is not supported", serverURL.Scheme)})
-	}
-
-	// Create OCSP Request
-	resp, err := executeOCSPCheck(cert, issuer, server, opts)
-	if err != nil {
-		// If there is a server error, attempt all servers before determining what to return
-		// to the user
-		return toServerResult(server, err)
-	}
-
-	// Validate OCSP response isn't expired
-	if time.Now().After(resp.NextUpdate) {
-		return toServerResult(server, GenericError{Err: errors.New("expired OCSP response")})
-	}
-
-	// Handle pkix-ocsp-no-check and id-ce-invalidityDate extensions if present
-	// in response
-	extensionMap := extensionsToMap(resp.Extensions)
-	if _, foundNoCheck := extensionMap[pkixNoCheckOID]; !foundNoCheck {
-		// This will be ignored until CRL is implemented
-		// If it isn't found, CRL should be used to verify the OCSP response
-		_ = foundNoCheck // needed to bypass linter warnings (Remove after adding CRL)
-		// TODO: add CRL support
-		// https://github.com/notaryproject/notation-core-go/issues/125
-	}
-	if invalidityDateBytes, foundInvalidityDate := extensionMap[invalidityDateOID]; foundInvalidityDate && !opts.SigningTime.IsZero() && resp.Status == ocsp.Revoked {
-		var invalidityDate time.Time
-		rest, err := asn1.UnmarshalWithParams(invalidityDateBytes, &invalidityDate, "generalized")
-		if len(rest) == 0 && err == nil && opts.SigningTime.Before(invalidityDate) {
-			return toServerResult(server, nil)
-		}
-	}
-
-	// No errors, valid server response
-	switch resp.Status {
-	case ocsp.Good:
-		return toServerResult(server, nil)
-	case ocsp.Revoked:
-		return toServerResult(server, RevokedError{})
-	default:
-		// ocsp.Unknown
-		return toServerResult(server, UnknownStatusError{})
-	}
-}
-
-func extensionsToMap(extensions []pkix.Extension) map[string][]byte {
-	extensionMap := make(map[string][]byte)
-	for _, extension := range extensions {
-		extensionMap[extension.Id.String()] = extension.Value
-	}
-	return extensionMap
-}
-
-func executeOCSPCheck(cert, issuer *x509.Certificate, server string, opts Options) (*ocsp.Response, error) {
-	// TODO: Look into other alternatives for specifying the Hash
-	// https://github.com/notaryproject/notation-core-go/issues/139
-	// The following do not support SHA256 hashes:
-	//  - Microsoft
-	//  - Entrust
-	//  - Let's Encrypt
-	//  - Digicert (sometimes)
-	// As this represents a large percentage of public CAs, we are using the
-	// hashing algorithm SHA1, which has been confirmed to be supported by all
-	// that were tested.
-	ocspRequest, err := ocsp.CreateRequest(cert, issuer, &ocsp.RequestOptions{Hash: crypto.SHA1})
-	if err != nil {
-		return nil, GenericError{Err: err}
-	}
-
-	var resp *http.Response
-	postRequired := base64.StdEncoding.EncodedLen(len(ocspRequest)) >= 255
-	if !postRequired {
-		encodedReq := url.QueryEscape(base64.StdEncoding.EncodeToString(ocspRequest))
-		if len(encodedReq) < 255 {
-			var reqURL string
-			reqURL, err = url.JoinPath(server, encodedReq)
-			if err != nil {
-				return nil, GenericError{Err: err}
-			}
-			resp, err = opts.HTTPClient.Get(reqURL)
-		} else {
-			resp, err = postRequest(ocspRequest, server, opts.HTTPClient)
-		}
-	} else {
-		resp, err = postRequest(ocspRequest, server, opts.HTTPClient)
-	}
-
-	if err != nil {
-		var urlErr *url.Error
-		if errors.As(err, &urlErr) && urlErr.Timeout() {
-			return nil, TimeoutError{}
-		}
-		return nil, GenericError{Err: err}
-	}
-	defer resp.Body.Close()
-
-	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
-		return nil, fmt.Errorf("failed to retrieve OCSP: response had status code %d", resp.StatusCode)
-	}
-
-	body, err := io.ReadAll(io.LimitReader(resp.Body, ocspMaxResponseSize))
-	if err != nil {
-		return nil, GenericError{Err: err}
-	}
-
-	switch {
-	case bytes.Equal(body, ocsp.UnauthorizedErrorResponse):
-		return nil, GenericError{Err: errors.New("OCSP unauthorized")}
-	case bytes.Equal(body, ocsp.MalformedRequestErrorResponse):
-		return nil, GenericError{Err: errors.New("OCSP malformed")}
-	case bytes.Equal(body, ocsp.InternalErrorErrorResponse):
-		return nil, GenericError{Err: errors.New("OCSP internal error")}
-	case bytes.Equal(body, ocsp.TryLaterErrorResponse):
-		return nil, GenericError{Err: errors.New("OCSP try later")}
-	case bytes.Equal(body, ocsp.SigRequredErrorResponse):
-		return nil, GenericError{Err: errors.New("OCSP signature required")}
-	}
-
-	return ocsp.ParseResponseForCert(body, cert, issuer)
-}
-
-func postRequest(req []byte, server string, httpClient *http.Client) (*http.Response, error) {
-	reader := bytes.NewReader(req)
-	return httpClient.Post(server, "application/ocsp-request", reader)
-}
-
-func toServerResult(server string, err error) *result.ServerResult {
-	switch t := err.(type) {
-	case nil:
-		return result.NewServerResult(result.ResultOK, server, nil)
-	case NoServerError:
-		return result.NewServerResult(result.ResultNonRevokable, server, nil)
-	case RevokedError:
-		return result.NewServerResult(result.ResultRevoked, server, t)
-	default:
-		// Includes GenericError, UnknownStatusError, result.InvalidChainError,
-		// and TimeoutError
-		return result.NewServerResult(result.ResultUnknown, server, t)
-	}
-}
-
-func serverResultsToCertRevocationResult(serverResults []*result.ServerResult) *result.CertRevocationResult {
-	return &result.CertRevocationResult{
-		Result:        serverResults[len(serverResults)-1].Result,
-		ServerResults: serverResults,
-	}
-}

revocation/ocsp/ocsp_test.go

@@ -21,6 +21,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/notaryproject/notation-core-go/revocation/purpose"
 	"github.com/notaryproject/notation-core-go/revocation/result"
 	"github.com/notaryproject/notation-core-go/testhelper"
 	"golang.org/x/crypto/ocsp"
@@ -78,79 +79,12 @@ func getRootCertResult() *result.CertRevocationResult {
 	}
 }
 
-func TestCheckStatus(t *testing.T) {
-	revokableCertTuple := testhelper.GetRevokableRSALeafCertificate()
-	revokableIssuerTuple := testhelper.GetRSARootCertificate()
-	ocspServer := revokableCertTuple.Cert.OCSPServer[0]
-	revokableChain := []*x509.Certificate{revokableCertTuple.Cert, revokableIssuerTuple.Cert}
-	testChain := []testhelper.RSACertTuple{revokableCertTuple, revokableIssuerTuple}
-
-	t.Run("check non-revoked cert", func(t *testing.T) {
-		client := testhelper.MockClient(testChain, []ocsp.ResponseStatus{ocsp.Good}, nil, true)
-		opts := Options{
-			CertChain:   revokableChain,
-			SigningTime: time.Now(),
-			HTTPClient:  client,
-		}
-
-		certResult := certCheckStatus(revokableChain[0], revokableChain[1], opts)
-		expectedCertResults := []*result.CertRevocationResult{getOKCertResult(ocspServer)}
-		validateEquivalentCertResults([]*result.CertRevocationResult{certResult}, expectedCertResults, t)
-	})
-	t.Run("check cert with Unknown OCSP response", func(t *testing.T) {
-		client := testhelper.MockClient(testChain, []ocsp.ResponseStatus{ocsp.Unknown}, nil, true)
-		opts := Options{
-			CertChain:   revokableChain,
-			SigningTime: time.Now(),
-			HTTPClient:  client,
-		}
-
-		certResult := certCheckStatus(revokableChain[0], revokableChain[1], opts)
-		expectedCertResults := []*result.CertRevocationResult{{
-			Result: result.ResultUnknown,
-			ServerResults: []*result.ServerResult{
-				result.NewServerResult(result.ResultUnknown, ocspServer, UnknownStatusError{}),
-			},
-		}}
-		validateEquivalentCertResults([]*result.CertRevocationResult{certResult}, expectedCertResults, t)
-	})
-	t.Run("check OCSP revoked cert", func(t *testing.T) {
-		client := testhelper.MockClient(testChain, []ocsp.ResponseStatus{ocsp.Revoked}, nil, true)
-		opts := Options{
-			CertChain:   revokableChain,
-			SigningTime: time.Now(),
-			HTTPClient:  client,
-		}
-
-		certResult := certCheckStatus(revokableChain[0], revokableChain[1], opts)
-		expectedCertResults := []*result.CertRevocationResult{{
-			Result: result.ResultRevoked,
-			ServerResults: []*result.ServerResult{
-				result.NewServerResult(result.ResultRevoked, ocspServer, RevokedError{}),
-			},
-		}}
-		validateEquivalentCertResults([]*result.CertRevocationResult{certResult}, expectedCertResults, t)
-	})
-	t.Run("check OCSP future revoked cert", func(t *testing.T) {
-		revokedTime := time.Now().Add(time.Hour)
-		client := testhelper.MockClient(testChain, []ocsp.ResponseStatus{ocsp.Revoked}, &revokedTime, true)
-		opts := Options{
-			CertChain:   revokableChain,
-			SigningTime: time.Now(),
-			HTTPClient:  client,
-		}
-
-		certResult := certCheckStatus(revokableChain[0], revokableChain[1], opts)
-		expectedCertResults := []*result.CertRevocationResult{getOKCertResult(ocspServer)}
-		validateEquivalentCertResults([]*result.CertRevocationResult{certResult}, expectedCertResults, t)
-	})
-}
-
 func TestCheckStatusForSelfSignedCert(t *testing.T) {
 	selfSignedTuple := testhelper.GetRSASelfSignedSigningCertTuple("Notation revocation test self-signed cert")
 	client := testhelper.MockClient([]testhelper.RSACertTuple{selfSignedTuple}, []ocsp.ResponseStatus{ocsp.Good}, nil, true)
 	opts := Options{
 		CertChain:        []*x509.Certificate{selfSignedTuple.Cert},
+		CertChainPurpose: purpose.CodeSigning,
 		SigningTime:      time.Now(),
 		HTTPClient:       client,
 	}
@@ -168,6 +102,7 @@ func TestCheckStatusForRootCert(t *testing.T) {
 	client := testhelper.MockClient([]testhelper.RSACertTuple{rootTuple}, []ocsp.ResponseStatus{ocsp.Good}, nil, true)
 	opts := Options{
 		CertChain:        []*x509.Certificate{rootTuple.Cert},
+		CertChainPurpose: purpose.CodeSigning,
 		SigningTime:      time.Now(),
 		HTTPClient:       client,
 	}
@@ -187,6 +122,7 @@ func TestCheckStatusForNonSelfSignedSingleCert(t *testing.T) {
 	client := testhelper.MockClient([]testhelper.RSACertTuple{certTuple}, []ocsp.ResponseStatus{ocsp.Good}, nil, true)
 	opts := Options{
 		CertChain:        []*x509.Certificate{certTuple.Cert},
+		CertChainPurpose: purpose.CodeSigning,
 		SigningTime:      time.Now(),
 		HTTPClient:       client,
 	}
@@ -213,6 +149,7 @@ func TestCheckStatusForChain(t *testing.T) {
 	t.Run("empty chain", func(t *testing.T) {
 		opts := Options{
 			CertChain:        []*x509.Certificate{},
+			CertChainPurpose: purpose.CodeSigning,
 			SigningTime:      time.Now(),
 			HTTPClient:       http.DefaultClient,
 		}
@@ -229,6 +166,7 @@ func TestCheckStatusForChain(t *testing.T) {
 		client := testhelper.MockClient(testChain, []ocsp.ResponseStatus{ocsp.Good}, nil, true)
 		opts := Options{
 			CertChain:        revokableChain,
+			CertChainPurpose: purpose.CodeSigning,
 			SigningTime:      time.Now(),
 			HTTPClient:       client,
 		}
@@ -252,6 +190,7 @@ func TestCheckStatusForChain(t *testing.T) {
 		// 3rd cert will be unknown, the rest will be good
 		opts := Options{
 			CertChain:        revokableChain,
+			CertChainPurpose: purpose.CodeSigning,
 			SigningTime:      time.Now(),
 			HTTPClient:       client,
 		}
@@ -280,6 +219,7 @@ func TestCheckStatusForChain(t *testing.T) {
 		// 3rd cert will be revoked, the rest will be good
 		opts := Options{
 			CertChain:        revokableChain,
+			CertChainPurpose: purpose.CodeSigning,
 			SigningTime:      time.Now(),
 			HTTPClient:       client,
 		}
@@ -308,6 +248,7 @@ func TestCheckStatusForChain(t *testing.T) {
 		// 3rd cert will be unknown, 5th will be revoked, the rest will be good
 		opts := Options{
 			CertChain:        revokableChain,
+			CertChainPurpose: purpose.CodeSigning,
 			SigningTime:      time.Now(),
 			HTTPClient:       client,
 		}
@@ -342,6 +283,7 @@ func TestCheckStatusForChain(t *testing.T) {
 		// 3rd cert will be revoked, the rest will be good
 		opts := Options{
 			CertChain:        revokableChain,
+			CertChainPurpose: purpose.CodeSigning,
 			SigningTime:      time.Now(),
 			HTTPClient:       client,
 		}
@@ -366,6 +308,7 @@ func TestCheckStatusForChain(t *testing.T) {
 		// 3rd cert will be unknown, 5th will be revoked, the rest will be good
 		opts := Options{
 			CertChain:        revokableChain,
+			CertChainPurpose: purpose.CodeSigning,
 			SigningTime:      time.Now(),
 			HTTPClient:       client,
 		}
@@ -394,6 +337,7 @@ func TestCheckStatusForChain(t *testing.T) {
 		// 3rd cert will be revoked, the rest will be good
 		opts := Options{
 			CertChain:        revokableChain,
+			CertChainPurpose: purpose.CodeSigning,
 			SigningTime:      time.Now().Add(time.Hour),
 			HTTPClient:       client,
 		}
@@ -423,6 +367,7 @@ func TestCheckStatusForChain(t *testing.T) {
 		// 3rd cert will be revoked, the rest will be good
 		opts := Options{
 			CertChain:        revokableChain,
+			CertChainPurpose: purpose.CodeSigning,
 			SigningTime:      zeroTime,
 			HTTPClient:       client,
 		}
@@ -465,15 +410,16 @@ func TestCheckStatusErrors(t *testing.T) {
 	expiredLeaf, _ := x509.ParseCertificate(revokableTuples[0].Cert.Raw)
 	expiredLeaf.IsCA = false
 	expiredLeaf.KeyUsage = x509.KeyUsageDigitalSignature
-	expiredLeaf.OCSPServer = []string{"http://example.com/expired_ocsp"}
+	expiredLeaf.OCSPServer = []string{"http://localhost.test/expired_ocsp"}
 	expiredChain := []*x509.Certificate{expiredLeaf, revokableTuples[1].Cert, revokableTuples[2].Cert}
 
 	noHTTPLeaf, _ := x509.ParseCertificate(revokableTuples[0].Cert.Raw)
 	noHTTPLeaf.IsCA = false
 	noHTTPLeaf.KeyUsage = x509.KeyUsageDigitalSignature
-	noHTTPLeaf.OCSPServer = []string{"ldap://ds.example.com:123/chain_ocsp/0"}
+	noHTTPLeaf.OCSPServer = []string{"ldap://ds.localhost.test:123/chain_ocsp/0"}
 	noHTTPChain := []*x509.Certificate{noHTTPLeaf, revokableTuples[1].Cert, revokableTuples[2].Cert}
 
+	timestampSigningCertErr := result.InvalidChainError{Err: errors.New("timestamp signing certificate with subject \"CN=Notation Test Revokable RSA Chain Cert 3,O=Notary,L=Seattle,ST=WA,C=US\" must have and only have Timestamping as extended key usage")}
 	backwardsChainErr := result.InvalidChainError{Err: errors.New("leaf certificate with subject \"CN=Notation Test Revokable RSA Chain Cert Root,O=Notary,L=Seattle,ST=WA,C=US\" is self-signed. Certificate chain must not contain self-signed leaf certificate")}
 	chainRootErr := result.InvalidChainError{Err: errors.New("root certificate with subject \"CN=Notation Test Revokable RSA Chain Cert 2,O=Notary,L=Seattle,ST=WA,C=US\" is not self-signed. Certificate chain must end with a valid self-signed root certificate")}
 	expiredRespErr := GenericError{Err: errors.New("expired OCSP response")}
@@ -482,6 +428,7 @@ func TestCheckStatusErrors(t *testing.T) {
 	t.Run("no OCSPServer specified", func(t *testing.T) {
 		opts := Options{
 			CertChain:        noOCSPChain,
+			CertChainPurpose: purpose.CodeSigning,
 			SigningTime:      time.Now(),
 			HTTPClient:       http.DefaultClient,
 		}
@@ -504,6 +451,7 @@ func TestCheckStatusErrors(t *testing.T) {
 	t.Run("chain missing root", func(t *testing.T) {
 		opts := Options{
 			CertChain:        noRootChain,
+			CertChainPurpose: purpose.CodeSigning,
 			SigningTime:      time.Now(),
 			HTTPClient:       http.DefaultClient,
 		}
@@ -519,6 +467,7 @@ func TestCheckStatusErrors(t *testing.T) {
 	t.Run("backwards chain", func(t *testing.T) {
 		opts := Options{
 			CertChain:        backwardsChain,
+			CertChainPurpose: purpose.CodeSigning,
 			SigningTime:      time.Now(),
 			HTTPClient:       http.DefaultClient,
 		}
@@ -531,10 +480,55 @@ func TestCheckStatusErrors(t *testing.T) {
 		}
 	})
 
+	t.Run("check codesigning cert with PurposeTimestamping", func(t *testing.T) {
+		opts := Options{
+			CertChain:        okChain,
+			CertChainPurpose: purpose.Timestamping,
+			SigningTime:      time.Now(),
+			HTTPClient:       http.DefaultClient,
+		}
+		certResults, err := CheckStatus(opts)
+		if err == nil || err.Error() != timestampSigningCertErr.Error() {
+			t.Errorf("Expected CheckStatus to fail with %v, but got: %v", timestampSigningCertErr, err)
+		}
+		if certResults != nil {
+			t.Error("Expected certResults to be nil when there is an error")
+		}
+	})
+
+	t.Run("check with default CertChainPurpose", func(t *testing.T) {
+		opts := Options{
+			CertChain:   okChain,
+			SigningTime: time.Now(),
+			HTTPClient:  http.DefaultClient,
+		}
+		_, err := CheckStatus(opts)
+		if err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	t.Run("check with unknwon CertChainPurpose", func(t *testing.T) {
+		opts := Options{
+			CertChain:        okChain,
+			CertChainPurpose: -1,
+			SigningTime:      time.Now(),
+			HTTPClient:       http.DefaultClient,
+		}
+		certResults, err := CheckStatus(opts)
+		if err == nil || err.Error() != "invalid chain: expected chain to be correct and complete: unsupported certificate chain purpose -1" {
+			t.Errorf("Expected CheckStatus to fail with %v, but got: %v", timestampSigningCertErr, err)
+		}
+		if certResults != nil {
+			t.Error("Expected certResults to be nil when there is an error")
+		}
+	})
+
 	t.Run("timeout", func(t *testing.T) {
 		timeoutClient := &http.Client{Timeout: 1 * time.Nanosecond}
 		opts := Options{
 			CertChain:        okChain,
+			CertChainPurpose: purpose.CodeSigning,
 			SigningTime:      time.Now(),
 			HTTPClient:       timeoutClient,
 		}
@@ -564,6 +558,7 @@ func TestCheckStatusErrors(t *testing.T) {
 		client := testhelper.MockClient(revokableTuples, []ocsp.ResponseStatus{ocsp.Good}, nil, true)
 		opts := Options{
 			CertChain:        expiredChain,
+			CertChainPurpose: purpose.CodeSigning,
 			SigningTime:      time.Now(),
 			HTTPClient:       client,
 		}
@@ -588,6 +583,7 @@ func TestCheckStatusErrors(t *testing.T) {
 		client := testhelper.MockClient(revokableTuples, []ocsp.ResponseStatus{ocsp.Good}, nil, false)
 		opts := Options{
 			CertChain:        okChain,
+			CertChainPurpose: purpose.CodeSigning,
 			SigningTime:      time.Now(),
 			HTTPClient:       client,
 		}
@@ -608,6 +604,7 @@ func TestCheckStatusErrors(t *testing.T) {
 		client := testhelper.MockClient(revokableTuples, []ocsp.ResponseStatus{ocsp.Good}, nil, true)
 		opts := Options{
 			CertChain:        noHTTPChain,
+			CertChainPurpose: purpose.CodeSigning,
 			SigningTime:      time.Now(),
 			HTTPClient:       client,
 		}
@@ -636,7 +633,7 @@ func TestCheckOCSPInvalidChain(t *testing.T) {
 	for i, cert := range misorderedIntermediateChain {
 		if i != (len(misorderedIntermediateChain) - 1) {
 			// Skip root which won't have an OCSP Server
-			cert.OCSPServer[0] = fmt.Sprintf("http://example.com/chain_ocsp/%d", i)
+			cert.OCSPServer[0] = fmt.Sprintf("http://localhost.test/chain_ocsp/%d", i)
 		}
 	}
 
@@ -644,7 +641,7 @@ func TestCheckOCSPInvalidChain(t *testing.T) {
 	for i, cert := range missingIntermediateChain {
 		if i != (len(missingIntermediateChain) - 1) {
 			// Skip root which won't have an OCSP Server
-			cert.OCSPServer[0] = fmt.Sprintf("http://example.com/chain_ocsp/%d", i)
+			cert.OCSPServer[0] = fmt.Sprintf("http://localhost.test/chain_ocsp/%d", i)
 		}
 	}
 
@@ -655,6 +652,7 @@ func TestCheckOCSPInvalidChain(t *testing.T) {
 		client := testhelper.MockClient(revokableTuples, []ocsp.ResponseStatus{ocsp.Good}, nil, true)
 		opts := Options{
 			CertChain:        missingIntermediateChain,
+			CertChainPurpose: purpose.CodeSigning,
 			SigningTime:      time.Now(),
 			HTTPClient:       client,
 		}
@@ -671,6 +669,7 @@ func TestCheckOCSPInvalidChain(t *testing.T) {
 		client := testhelper.MockClient(misorderedIntermediateTuples, []ocsp.ResponseStatus{ocsp.Good}, nil, true)
 		opts := Options{
 			CertChain:        misorderedIntermediateChain,
+			CertChainPurpose: purpose.CodeSigning,
 			SigningTime:      time.Now(),
 			HTTPClient:       client,
 		}

revocation/purpose/purpose.go

@@ -0,0 +1,28 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package purpose provides purposes of the certificate chain whose revocation
+// status is checked
+package purpose
+
+// Purpose is an enum for purpose of the certificate chain whose revocation
+// status is checked
+type Purpose int
+
+const (
+	// CodeSigning means the certificate chain is a code signing chain
+	CodeSigning Purpose = iota
+
+	// Timestamping means the certificate chain is a timestamping chain
+	Timestamping
+)

revocation/result/results.go

@@ -16,23 +16,27 @@ package result
 
 import "strconv"
 
-// Result is a type of enumerated value to help characterize errors. It can be
+// Result is a type of enumerated value to help characterize revocation result.
-// OK, Unknown, or Revoked
+// It can be OK, Unknown, NonRevokable, or Revoked
 type Result int
 
 const (
 	// ResultUnknown is a Result that indicates that some error other than a
-	// revocation was encountered during the revocation check
+	// revocation was encountered during the revocation check.
 	ResultUnknown Result = iota
-	// ResultOK is a Result that indicates that the revocation check resulted in no
+
-	// important errors
+	// ResultOK is a Result that indicates that the revocation check resulted in
+	// no important errors.
 	ResultOK
-	// ResultNonRevokable is a Result that indicates that the certificate cannot be
+
-	// checked for revocation. This may be a result of no OCSP servers being
+	// ResultNonRevokable is a Result that indicates that the certificate cannot
-	// specified, the cert is a root certificate, or other related situations.
+	// be checked for revocation. This may be due to the absence of OCSP servers
+	// or CRL distribution points, or because the certificate is a root
+	// certificate.
 	ResultNonRevokable
+
 	// ResultRevoked is a Result that indicates that at least one certificate was
-	// revoked when performing a revocation check on the certificate chain
+	// revoked when performing a revocation check on the certificate chain.
 	ResultRevoked
 )
 
@@ -52,8 +56,45 @@ func (r Result) String() string {
 	}
 }
 
-// ServerResult encapsulates the result for a single server for a single
+// RevocationMethod defines the method used to check the revocation status of a
-// certificate in the chain
+// certificate.
+type RevocationMethod int
+
+const (
+	// RevocationMethodUnknown is used for root certificates or when the method
+	// used to check the revocation status of a certificate is unknown.
+	RevocationMethodUnknown RevocationMethod = iota
+
+	// RevocationMethodOCSP represents OCSP as the method used to check the
+	// revocation status of a certificate.
+	RevocationMethodOCSP
+
+	// RevocationMethodCRL represents CRL as the method used to check the
+	// revocation status of a certificate.
+	RevocationMethodCRL
+
+	// RevocationMethodOCSPFallbackCRL represents OCSP check with unknown error
+	// fallback to CRL as the method used to check the revocation status of a
+	// certificate.
+	RevocationMethodOCSPFallbackCRL
+)
+
+// String provides a conversion from a Method to a string
+func (m RevocationMethod) String() string {
+	switch m {
+	case RevocationMethodOCSP:
+		return "OCSP"
+	case RevocationMethodCRL:
+		return "CRL"
+	case RevocationMethodOCSPFallbackCRL:
+		return "OCSPFallbackCRL"
+	default:
+		return "Unknown"
+	}
+}
+
+// ServerResult encapsulates the OCSP result for a single server or the CRL
+// result for a single CRL URI for a certificate in the chain
 type ServerResult struct {
 	// Result of revocation for this server (Unknown if there is an error which
 	// prevents the retrieval of a valid status)
@@ -67,6 +108,11 @@ type ServerResult struct {
 	// Error is set if there is an error associated with the revocation check
 	// to this server
 	Error error
+
+	// RevocationMethod is the method used to check the revocation status of the
+	// certificate, including RevocationMethodUnknown, RevocationMethodOCSP,
+	// RevocationMethodCRL
+	RevocationMethod RevocationMethod
 }
 
 // NewServerResult creates a ServerResult object from its individual parts: a
@@ -83,21 +129,31 @@ func NewServerResult(result Result, server string, err error) *ServerResult {
 // chain as well as the results from individual servers associated with this
 // certificate
 type CertRevocationResult struct {
-	// Result of revocation for a specific cert in the chain
+	// Result of revocation for a specific certificate in the chain.
-	//
-	// If there are multiple ServerResults, this is because no responses were
-	// able to be retrieved, leaving each ServerResult with a Result of Unknown.
-	// Thus, in the case of more than one ServerResult, this will be ResultUnknown
 	Result Result
 
-	// An array of results for each server associated with the certificate.
+	// ServerResults is an array of results for each server associated with the
-	// The length will be either 1 or the number of OCSPServers for the cert.
+	// certificate.
 	//
-	// If the length is 1, then a valid status was able to be retrieved. Only
+	// When RevocationMethod is MethodOCSP, the length will be
+	// either 1 or the number of OCSPServers for the certificate.
+	// If the length is 1, then a valid status was retrieved. Only
 	// this server result is contained. Any errors for other servers are
 	// discarded in favor of this valid response.
-	//
 	// Otherwise, every server specified had some error that prevented the
-	// status from being retrieved. These are all contained here for evaluation
+	// status from being retrieved. These are all contained here for evaluation.
+	//
+	// When RevocationMethod is MethodCRL, the length will be the number of
+	// CRL distribution points' URIs checked. If the result is Revoked, or
+	// there is an error, the length will be 1.
+	//
+	// When RevocationMethod is MethodOCSPFallbackCRL, the length
+	// will be the sum of the previous two cases. The CRL result will be
+	// appended after the OCSP results.
 	ServerResults []*ServerResult
+
+	// RevocationMethod is the method used to check the revocation status of the
+	// certificate, including RevocationMethodUnknown, RevocationMethodOCSP,
+	// RevocationMethodCRL and RevocationMethodOCSPFallbackCRL
+	RevocationMethod RevocationMethod
 }

revocation/result/results_test.go

@@ -46,6 +46,27 @@ func TestResultString(t *testing.T) {
 	})
 }
 
+func TestMethodString(t *testing.T) {
+	tests := []struct {
+		method   RevocationMethod
+		expected string
+	}{
+		{RevocationMethodOCSP, "OCSP"},
+		{RevocationMethodCRL, "CRL"},
+		{RevocationMethodOCSPFallbackCRL, "OCSPFallbackCRL"},
+		{RevocationMethod(999), "Unknown"}, // Test for default case
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.expected, func(t *testing.T) {
+			result := tt.method.String()
+			if result != tt.expected {
+				t.Errorf("expected %s, got %s", tt.expected, result)
+			}
+		})
+	}
+}
+
 func TestNewServerResult(t *testing.T) {
 	expectedR := &ServerResult{
 		Result: ResultNonRevokable,

revocation/revocation.go

@@ -16,50 +16,256 @@
 package revocation
 
 import (
+	"context"
 	"crypto/x509"
 	"errors"
+	"fmt"
 	"net/http"
+	"sync"
 	"time"
 
-	"github.com/notaryproject/notation-core-go/revocation/ocsp"
+	crlutil "github.com/notaryproject/notation-core-go/revocation/crl"
+	"github.com/notaryproject/notation-core-go/revocation/internal/crl"
+	"github.com/notaryproject/notation-core-go/revocation/internal/ocsp"
+	"github.com/notaryproject/notation-core-go/revocation/internal/x509util"
+	"github.com/notaryproject/notation-core-go/revocation/purpose"
 	"github.com/notaryproject/notation-core-go/revocation/result"
 )
 
-// Revocation is an interface that specifies methods used for revocation checking
+// Revocation is an interface that specifies methods used for revocation checking.
+//
+// Deprecated: Revocation exists for backwards compatibility and should not be used.
+// To perform revocation check, use [Validator].
 type Revocation interface {
 	// Validate checks the revocation status for a certificate chain using OCSP
+	// and CRL if OCSP is not available. It returns an array of
+	// CertRevocationResults that contain the results and any errors that are
+	// encountered during the process
+	Validate(certChain []*x509.Certificate, signingTime time.Time) ([]*result.CertRevocationResult, error)
+}
+
+// ValidateContextOptions provides configuration options for revocation checks
+type ValidateContextOptions struct {
+	// CertChain denotes the certificate chain whose revocation status is
+	// been validated. REQUIRED.
+	CertChain []*x509.Certificate
+
+	// AuthenticSigningTime denotes the authentic signing time of the signature.
+	// It is used to compare with the InvalidityDate during revocation check.
+	// OPTIONAL.
+	//
+	// Reference: https://github.com/notaryproject/specifications/blob/v1.0.0/specs/trust-store-trust-policy.md#revocation-checking-with-ocsp
+	AuthenticSigningTime time.Time
+}
+
+// Validator is an interface that provides revocation checking with
+// context
+type Validator interface {
+	// ValidateContext checks the revocation status given caller provided options
 	// and returns an array of CertRevocationResults that contain the results
 	// and any errors that are encountered during the process
-	Validate(certChain []*x509.Certificate, signingTime time.Time) ([]*result.CertRevocationResult, error)
+	ValidateContext(ctx context.Context, validateContextOpts ValidateContextOptions) ([]*result.CertRevocationResult, error)
 }
 
 // revocation is an internal struct used for revocation checking
 type revocation struct {
-	httpClient *http.Client
+	ocspHTTPClient   *http.Client
+	crlFetcher       crlutil.Fetcher
+	certChainPurpose purpose.Purpose
 }
 
-// New constructs a revocation object
+// New constructs a revocation object for code signing certificate chain.
+//
+// Deprecated: New exists for backwards compatibility and should not be used.
+// To create a revocation object, use [NewWithOptions].
 func New(httpClient *http.Client) (Revocation, error) {
 	if httpClient == nil {
 		return nil, errors.New("invalid input: a non-nil httpClient must be specified")
 	}
+	fetcher, err := crlutil.NewHTTPFetcher(httpClient)
+	if err != nil {
+		return nil, err
+	}
+
 	return &revocation{
-		httpClient: httpClient,
+		ocspHTTPClient:   httpClient,
+		crlFetcher:       fetcher,
+		certChainPurpose: purpose.CodeSigning,
+	}, nil
+}
+
+// Options specifies values that are needed to check revocation
+type Options struct {
+	// OCSPHTTPClient is the HTTP client for OCSP request. If not provided,
+	// a default *http.Client with timeout of 2 seconds will be used.
+	// OPTIONAL.
+	OCSPHTTPClient *http.Client
+
+	// CRLFetcher is a fetcher for CRL with cache. If not provided, a default
+	// fetcher with an HTTP client and a timeout of 5 seconds will be used
+	// without cache.
+	CRLFetcher crlutil.Fetcher
+
+	// CertChainPurpose is the purpose of the certificate chain. Supported
+	// values are CodeSigning and Timestamping. Default value is CodeSigning.
+	// OPTIONAL.
+	CertChainPurpose purpose.Purpose
+}
+
+// NewWithOptions constructs a Validator with the specified options
+func NewWithOptions(opts Options) (Validator, error) {
+	if opts.OCSPHTTPClient == nil {
+		opts.OCSPHTTPClient = &http.Client{Timeout: 2 * time.Second}
+	}
+
+	fetcher := opts.CRLFetcher
+	if fetcher == nil {
+		newFetcher, err := crlutil.NewHTTPFetcher(&http.Client{Timeout: 5 * time.Second})
+		if err != nil {
+			return nil, err
+		}
+		fetcher = newFetcher
+	}
+
+	switch opts.CertChainPurpose {
+	case purpose.CodeSigning, purpose.Timestamping:
+	default:
+		return nil, fmt.Errorf("unsupported certificate chain purpose %v", opts.CertChainPurpose)
+	}
+
+	return &revocation{
+		ocspHTTPClient:   opts.OCSPHTTPClient,
+		crlFetcher:       fetcher,
+		certChainPurpose: opts.CertChainPurpose,
 	}, nil
 }
 
 // Validate checks the revocation status for a certificate chain using OCSP and
-// returns an array of CertRevocationResults that contain the results and any
+// CRL if OCSP is not available. It returns an array of CertRevocationResults
-// errors that are encountered during the process
+// that contain the results and any errors that are encountered during the
+// process.
 //
-// TODO: add CRL support
+// This function tries OCSP and falls back to CRL when:
-// https://github.com/notaryproject/notation-core-go/issues/125
+// - OCSP is not supported by the certificate
+// - OCSP returns an unknown status
+//
+// NOTE: The certificate chain is expected to be in the order of leaf to root.
 func (r *revocation) Validate(certChain []*x509.Certificate, signingTime time.Time) ([]*result.CertRevocationResult, error) {
-	return ocsp.CheckStatus(ocsp.Options{
+	return r.ValidateContext(context.Background(), ValidateContextOptions{
 		CertChain:            certChain,
-		SigningTime: signingTime,
+		AuthenticSigningTime: signingTime,
-		HTTPClient:  r.httpClient,
 	})
-	// TODO: add CRL support
+}
-	// https://github.com/notaryproject/notation-core-go/issues/125
+
+// ValidateContext checks the revocation status for a certificate chain using OCSP and
+// CRL if OCSP is not available. It returns an array of CertRevocationResults
+// that contain the results and any errors that are encountered during the
+// process.
+//
+// This function tries OCSP and falls back to CRL when:
+// - OCSP is not supported by the certificate
+// - OCSP returns an unknown status
+//
+// NOTE: The certificate chain is expected to be in the order of leaf to root.
+func (r *revocation) ValidateContext(ctx context.Context, validateContextOpts ValidateContextOptions) ([]*result.CertRevocationResult, error) {
+	// validate certificate chain
+	if len(validateContextOpts.CertChain) == 0 {
+		return nil, result.InvalidChainError{Err: errors.New("chain does not contain any certificates")}
+	}
+	certChain := validateContextOpts.CertChain
+	if err := x509util.ValidateChain(certChain, r.certChainPurpose); err != nil {
+		return nil, err
+	}
+
+	ocspOpts := ocsp.CertCheckStatusOptions{
+		HTTPClient:  r.ocspHTTPClient,
+		SigningTime: validateContextOpts.AuthenticSigningTime,
+	}
+
+	crlOpts := crl.CertCheckStatusOptions{
+		Fetcher:     r.crlFetcher,
+		SigningTime: validateContextOpts.AuthenticSigningTime,
+	}
+
+	// panicChain is used to store the panic in goroutine and handle it
+	panicChan := make(chan any, len(certChain))
+	defer close(panicChan)
+
+	certResults := make([]*result.CertRevocationResult, len(certChain))
+	var wg sync.WaitGroup
+	for i, cert := range certChain[:len(certChain)-1] {
+		switch {
+		case ocsp.Supported(cert):
+			// do OCSP check for the certificate
+			wg.Add(1)
+
+			go func(i int, cert *x509.Certificate) {
+				defer wg.Done()
+				defer func() {
+					if r := recover(); r != nil {
+						// catch panic and send it to panicChan to avoid
+						// losing the panic
+						panicChan <- r
+					}
+				}()
+
+				ocspResult := ocsp.CertCheckStatus(ctx, cert, certChain[i+1], ocspOpts)
+				if ocspResult != nil && ocspResult.Result == result.ResultUnknown && crl.Supported(cert) {
+					// try CRL check if OCSP serverResult is unknown
+					serverResult := crl.CertCheckStatus(ctx, cert, certChain[i+1], crlOpts)
+					// append CRL result to OCSP result
+					serverResult.ServerResults = append(ocspResult.ServerResults, serverResult.ServerResults...)
+					serverResult.RevocationMethod = result.RevocationMethodOCSPFallbackCRL
+					certResults[i] = serverResult
+				} else {
+					certResults[i] = ocspResult
+				}
+			}(i, cert)
+		case crl.Supported(cert):
+			// do CRL check for the certificate
+			wg.Add(1)
+
+			go func(i int, cert *x509.Certificate) {
+				defer wg.Done()
+				defer func() {
+					if r := recover(); r != nil {
+						// catch panic and send it to panicChan to avoid
+						// losing the panic
+						panicChan <- r
+					}
+				}()
+
+				certResults[i] = crl.CertCheckStatus(ctx, cert, certChain[i+1], crlOpts)
+			}(i, cert)
+		default:
+			certResults[i] = &result.CertRevocationResult{
+				Result: result.ResultNonRevokable,
+				ServerResults: []*result.ServerResult{{
+					Result:           result.ResultNonRevokable,
+					RevocationMethod: result.RevocationMethodUnknown,
+				}},
+				RevocationMethod: result.RevocationMethodUnknown,
+			}
+		}
+	}
+
+	// Last is root cert, which will never be revoked by OCSP or CRL
+	certResults[len(certChain)-1] = &result.CertRevocationResult{
+		Result: result.ResultNonRevokable,
+		ServerResults: []*result.ServerResult{{
+			Result:           result.ResultNonRevokable,
+			RevocationMethod: result.RevocationMethodUnknown,
+		}},
+		RevocationMethod: result.RevocationMethodUnknown,
+	}
+	wg.Wait()
+
+	// handle panic
+	select {
+	case p := <-panicChan:
+		panic(p)
+	default:
+	}
+
+	return certResults, nil
 }

revocation/revocation_test.go

@@ -14,14 +14,23 @@
 package revocation
 
 import (
+	"bytes"
+	"context"
+	"crypto/rand"
 	"crypto/x509"
 	"errors"
 	"fmt"
+	"io"
+	"math/big"
 	"net/http"
+	"strconv"
+	"strings"
 	"testing"
 	"time"
 
-	revocationocsp "github.com/notaryproject/notation-core-go/revocation/ocsp"
+	"github.com/notaryproject/notation-core-go/revocation/crl"
+	revocationocsp "github.com/notaryproject/notation-core-go/revocation/internal/ocsp"
+	"github.com/notaryproject/notation-core-go/revocation/purpose"
 	"github.com/notaryproject/notation-core-go/revocation/result"
 	"github.com/notaryproject/notation-core-go/testhelper"
 	"golang.org/x/crypto/ocsp"
@@ -58,6 +67,9 @@ func validateEquivalentCertResults(certResults, expectedCertResults []*result.Ce
 				t.Errorf("Expected certResults[%d].ServerResults[%d].Error to be %v, but got %v", i, j, expectedCertResults[i].ServerResults[j].Error, serverResult.Error)
 			}
 		}
+		if certResult.RevocationMethod != expectedCertResults[i].RevocationMethod {
+			t.Errorf("Expected certResults[%d].RevocationMethod to be %d, but got %d", i, expectedCertResults[i].RevocationMethod, certResult.RevocationMethod)
+		}
 	}
 }
 
@@ -67,6 +79,7 @@ func getOKCertResult(server string) *result.CertRevocationResult {
 		ServerResults: []*result.ServerResult{
 			result.NewServerResult(result.ResultOK, server, nil),
 		},
+		RevocationMethod: result.RevocationMethodOCSP,
 	}
 }
 
@@ -94,11 +107,34 @@ func TestNew(t *testing.T) {
 	revR, ok := r.(*revocation)
 	if !ok {
 		t.Error("Expected New to create an object matching the internal revocation struct")
-	} else if revR.httpClient != client {
+	} else if revR.ocspHTTPClient != client {
-		t.Errorf("Expected New to set client to %v, but it was set to %v", client, revR.httpClient)
+		t.Errorf("Expected New to set client to %v, but it was set to %v", client, revR.ocspHTTPClient)
 	}
 }
 
+func TestNewWithOptions(t *testing.T) {
+	t.Run("nil OCSP HTTP Client", func(t *testing.T) {
+		_, err := NewWithOptions(Options{
+			CertChainPurpose: purpose.CodeSigning,
+		})
+		if err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	t.Run("invalid CertChainPurpose", func(t *testing.T) {
+		_, err := NewWithOptions(Options{
+			OCSPHTTPClient:   &http.Client{},
+			CertChainPurpose: -1,
+		})
+		expectedErrMsg := "unsupported certificate chain purpose -1"
+		if err == nil || err.Error() != expectedErrMsg {
+			t.Fatalf("expected %s, but got %s", expectedErrMsg, err.Error())
+		}
+	})
+
+}
+
 func TestCheckRevocationStatusForSingleCert(t *testing.T) {
 	revokableCertTuple := testhelper.GetRevokableRSALeafCertificate()
 	revokableIssuerTuple := testhelper.GetRSARootCertificate()
@@ -136,6 +172,7 @@ func TestCheckRevocationStatusForSingleCert(t *testing.T) {
 				ServerResults: []*result.ServerResult{
 					result.NewServerResult(result.ResultUnknown, revokableChain[0].OCSPServer[0], revocationocsp.UnknownStatusError{}),
 				},
+				RevocationMethod: result.RevocationMethodOCSP,
 			},
 			getRootCertResult(),
 		}
@@ -158,6 +195,7 @@ func TestCheckRevocationStatusForSingleCert(t *testing.T) {
 				ServerResults: []*result.ServerResult{
 					result.NewServerResult(result.ResultRevoked, revokableChain[0].OCSPServer[0], revocationocsp.RevokedError{}),
 				},
+				RevocationMethod: result.RevocationMethodOCSP,
 			},
 			getRootCertResult(),
 		}
@@ -280,6 +318,7 @@ func TestCheckRevocationStatusForChain(t *testing.T) {
 				ServerResults: []*result.ServerResult{
 					result.NewServerResult(result.ResultUnknown, revokableChain[2].OCSPServer[0], revocationocsp.UnknownStatusError{}),
 				},
+				RevocationMethod: result.RevocationMethodOCSP,
 			},
 			getOKCertResult(revokableChain[3].OCSPServer[0]),
 			getOKCertResult(revokableChain[4].OCSPServer[0]),
@@ -307,6 +346,7 @@ func TestCheckRevocationStatusForChain(t *testing.T) {
 				ServerResults: []*result.ServerResult{
 					result.NewServerResult(result.ResultRevoked, revokableChain[2].OCSPServer[0], revocationocsp.RevokedError{}),
 				},
+				RevocationMethod: result.RevocationMethodOCSP,
 			},
 			getOKCertResult(revokableChain[3].OCSPServer[0]),
 			getOKCertResult(revokableChain[4].OCSPServer[0]),
@@ -334,6 +374,7 @@ func TestCheckRevocationStatusForChain(t *testing.T) {
 				ServerResults: []*result.ServerResult{
 					result.NewServerResult(result.ResultUnknown, revokableChain[2].OCSPServer[0], revocationocsp.UnknownStatusError{}),
 				},
+				RevocationMethod: result.RevocationMethodOCSP,
 			},
 			getOKCertResult(revokableChain[3].OCSPServer[0]),
 			{
@@ -341,6 +382,7 @@ func TestCheckRevocationStatusForChain(t *testing.T) {
 				ServerResults: []*result.ServerResult{
 					result.NewServerResult(result.ResultRevoked, revokableChain[4].OCSPServer[0], revocationocsp.RevokedError{}),
 				},
+				RevocationMethod: result.RevocationMethodOCSP,
 			},
 			getRootCertResult(),
 		}
@@ -390,6 +432,7 @@ func TestCheckRevocationStatusForChain(t *testing.T) {
 				ServerResults: []*result.ServerResult{
 					result.NewServerResult(result.ResultUnknown, revokableChain[2].OCSPServer[0], revocationocsp.UnknownStatusError{}),
 				},
+				RevocationMethod: result.RevocationMethodOCSP,
 			},
 			getOKCertResult(revokableChain[3].OCSPServer[0]),
 			getOKCertResult(revokableChain[4].OCSPServer[0]),
@@ -417,6 +460,7 @@ func TestCheckRevocationStatusForChain(t *testing.T) {
 				ServerResults: []*result.ServerResult{
 					result.NewServerResult(result.ResultRevoked, revokableChain[2].OCSPServer[0], revocationocsp.RevokedError{}),
 				},
+				RevocationMethod: result.RevocationMethodOCSP,
 			},
 			getOKCertResult(revokableChain[3].OCSPServer[0]),
 			getOKCertResult(revokableChain[4].OCSPServer[0]),
@@ -450,6 +494,313 @@ func TestCheckRevocationStatusForChain(t *testing.T) {
 				ServerResults: []*result.ServerResult{
 					result.NewServerResult(result.ResultRevoked, revokableChain[2].OCSPServer[0], revocationocsp.RevokedError{}),
 				},
+				RevocationMethod: result.RevocationMethodOCSP,
+			},
+			getOKCertResult(revokableChain[3].OCSPServer[0]),
+			getOKCertResult(revokableChain[4].OCSPServer[0]),
+			getRootCertResult(),
+		}
+		validateEquivalentCertResults(certResults, expectedCertResults, t)
+	})
+}
+
+func TestCheckRevocationStatusForTimestampChain(t *testing.T) {
+	zeroTime := time.Time{}
+	testChain := testhelper.GetRevokableRSATimestampChain(6)
+	revokableChain := make([]*x509.Certificate, 6)
+	for i, tuple := range testChain {
+		revokableChain[i] = tuple.Cert
+		revokableChain[i].NotBefore = zeroTime
+	}
+
+	t.Run("invalid revocation purpose", func(t *testing.T) {
+		revocationClient := &revocation{
+			ocspHTTPClient:   &http.Client{Timeout: 5 * time.Second},
+			certChainPurpose: -1,
+		}
+
+		_, err := revocationClient.Validate(revokableChain, time.Now())
+		if err == nil {
+			t.Error("Expected Validate to fail with an error, but it succeeded")
+		}
+	})
+
+	t.Run("empty chain", func(t *testing.T) {
+		r, err := NewWithOptions(Options{
+			OCSPHTTPClient:   &http.Client{Timeout: 5 * time.Second},
+			CertChainPurpose: purpose.Timestamping,
+		})
+		if err != nil {
+			t.Errorf("Expected successful creation of revocation, but received error: %v", err)
+		}
+		certResults, err := r.ValidateContext(context.Background(), ValidateContextOptions{
+			CertChain:            []*x509.Certificate{},
+			AuthenticSigningTime: time.Now(),
+		})
+		expectedErr := result.InvalidChainError{Err: errors.New("chain does not contain any certificates")}
+		if err == nil || err.Error() != expectedErr.Error() {
+			t.Errorf("Expected CheckStatus to fail with %v, but got: %v", expectedErr, err)
+		}
+		if certResults != nil {
+			t.Error("Expected certResults to be nil when there is an error")
+		}
+	})
+	t.Run("check non-revoked chain", func(t *testing.T) {
+		client := testhelper.MockClient(testChain, []ocsp.ResponseStatus{ocsp.Good}, nil, true)
+		r, err := NewWithOptions(Options{
+			OCSPHTTPClient:   client,
+			CertChainPurpose: purpose.Timestamping,
+		})
+		if err != nil {
+			t.Errorf("Expected successful creation of revocation, but received error: %v", err)
+		}
+		certResults, err := r.ValidateContext(context.Background(), ValidateContextOptions{
+			CertChain:            revokableChain,
+			AuthenticSigningTime: time.Now(),
+		})
+		if err != nil {
+			t.Errorf("Expected CheckStatus to succeed, but got error: %v", err)
+		}
+		expectedCertResults := []*result.CertRevocationResult{
+			getOKCertResult(revokableChain[0].OCSPServer[0]),
+			getOKCertResult(revokableChain[1].OCSPServer[0]),
+			getOKCertResult(revokableChain[2].OCSPServer[0]),
+			getOKCertResult(revokableChain[3].OCSPServer[0]),
+			getOKCertResult(revokableChain[4].OCSPServer[0]),
+			getRootCertResult(),
+		}
+		validateEquivalentCertResults(certResults, expectedCertResults, t)
+	})
+	t.Run("check chain with 1 Unknown cert", func(t *testing.T) {
+		// 3rd cert will be unknown, the rest will be good
+		client := testhelper.MockClient(testChain, []ocsp.ResponseStatus{ocsp.Good, ocsp.Good, ocsp.Unknown, ocsp.Good}, nil, true)
+		r, err := NewWithOptions(Options{
+			OCSPHTTPClient:   client,
+			CertChainPurpose: purpose.Timestamping,
+		})
+		if err != nil {
+			t.Errorf("Expected successful creation of revocation, but received error: %v", err)
+		}
+		certResults, err := r.ValidateContext(context.Background(), ValidateContextOptions{
+			CertChain:            revokableChain,
+			AuthenticSigningTime: time.Now(),
+		})
+		if err != nil {
+			t.Errorf("Expected CheckStatus to succeed, but got error: %v", err)
+		}
+		expectedCertResults := []*result.CertRevocationResult{
+			getOKCertResult(revokableChain[0].OCSPServer[0]),
+			getOKCertResult(revokableChain[1].OCSPServer[0]),
+			{
+				Result: result.ResultUnknown,
+				ServerResults: []*result.ServerResult{
+					result.NewServerResult(result.ResultUnknown, revokableChain[2].OCSPServer[0], revocationocsp.UnknownStatusError{}),
+				},
+				RevocationMethod: result.RevocationMethodOCSP,
+			},
+			getOKCertResult(revokableChain[3].OCSPServer[0]),
+			getOKCertResult(revokableChain[4].OCSPServer[0]),
+			getRootCertResult(),
+		}
+		validateEquivalentCertResults(certResults, expectedCertResults, t)
+	})
+	t.Run("check OCSP with 1 revoked cert", func(t *testing.T) {
+		// 3rd cert will be revoked, the rest will be good
+		client := testhelper.MockClient(testChain, []ocsp.ResponseStatus{ocsp.Good, ocsp.Good, ocsp.Revoked, ocsp.Good}, nil, true)
+		r, err := NewWithOptions(Options{
+			OCSPHTTPClient:   client,
+			CertChainPurpose: purpose.Timestamping,
+		})
+		if err != nil {
+			t.Errorf("Expected successful creation of revocation, but received error: %v", err)
+		}
+		certResults, err := r.ValidateContext(context.Background(), ValidateContextOptions{
+			CertChain:            revokableChain,
+			AuthenticSigningTime: time.Now(),
+		})
+		if err != nil {
+			t.Errorf("Expected CheckStatus to succeed, but got error: %v", err)
+		}
+		expectedCertResults := []*result.CertRevocationResult{
+			getOKCertResult(revokableChain[0].OCSPServer[0]),
+			getOKCertResult(revokableChain[1].OCSPServer[0]),
+			{
+				Result: result.ResultRevoked,
+				ServerResults: []*result.ServerResult{
+					result.NewServerResult(result.ResultRevoked, revokableChain[2].OCSPServer[0], revocationocsp.RevokedError{}),
+				},
+				RevocationMethod: result.RevocationMethodOCSP,
+			},
+			getOKCertResult(revokableChain[3].OCSPServer[0]),
+			getOKCertResult(revokableChain[4].OCSPServer[0]),
+			getRootCertResult(),
+		}
+		validateEquivalentCertResults(certResults, expectedCertResults, t)
+	})
+	t.Run("check OCSP with 1 unknown and 1 revoked cert", func(t *testing.T) {
+		// 3rd cert will be unknown, 5th will be revoked, the rest will be good
+		client := testhelper.MockClient(testChain, []ocsp.ResponseStatus{ocsp.Good, ocsp.Good, ocsp.Unknown, ocsp.Good, ocsp.Revoked, ocsp.Good}, nil, true)
+		r, err := NewWithOptions(Options{
+			OCSPHTTPClient:   client,
+			CertChainPurpose: purpose.Timestamping,
+		})
+		if err != nil {
+			t.Errorf("Expected successful creation of revocation, but received error: %v", err)
+		}
+		certResults, err := r.ValidateContext(context.Background(), ValidateContextOptions{
+			CertChain:            revokableChain,
+			AuthenticSigningTime: time.Now(),
+		})
+		if err != nil {
+			t.Errorf("Expected CheckStatus to succeed, but got error: %v", err)
+		}
+		expectedCertResults := []*result.CertRevocationResult{
+			getOKCertResult(revokableChain[0].OCSPServer[0]),
+			getOKCertResult(revokableChain[1].OCSPServer[0]),
+			{
+				Result: result.ResultUnknown,
+				ServerResults: []*result.ServerResult{
+					result.NewServerResult(result.ResultUnknown, revokableChain[2].OCSPServer[0], revocationocsp.UnknownStatusError{}),
+				},
+				RevocationMethod: result.RevocationMethodOCSP,
+			},
+			getOKCertResult(revokableChain[3].OCSPServer[0]),
+			{
+				Result: result.ResultRevoked,
+				ServerResults: []*result.ServerResult{
+					result.NewServerResult(result.ResultRevoked, revokableChain[4].OCSPServer[0], revocationocsp.RevokedError{}),
+				},
+				RevocationMethod: result.RevocationMethodOCSP,
+			},
+			getRootCertResult(),
+		}
+		validateEquivalentCertResults(certResults, expectedCertResults, t)
+	})
+	t.Run("check OCSP with 1 future revoked cert", func(t *testing.T) {
+		revokedTime := time.Now().Add(time.Hour)
+		// 3rd cert will be future revoked, the rest will be good
+		client := testhelper.MockClient(testChain, []ocsp.ResponseStatus{ocsp.Good, ocsp.Good, ocsp.Revoked, ocsp.Good}, &revokedTime, true)
+		r, err := NewWithOptions(Options{
+			OCSPHTTPClient:   client,
+			CertChainPurpose: purpose.Timestamping,
+		})
+		if err != nil {
+			t.Errorf("Expected successful creation of revocation, but received error: %v", err)
+		}
+		certResults, err := r.ValidateContext(context.Background(), ValidateContextOptions{
+			CertChain:            revokableChain,
+			AuthenticSigningTime: time.Now(),
+		})
+		if err != nil {
+			t.Errorf("Expected CheckStatus to succeed, but got error: %v", err)
+		}
+		expectedCertResults := []*result.CertRevocationResult{
+			getOKCertResult(revokableChain[0].OCSPServer[0]),
+			getOKCertResult(revokableChain[1].OCSPServer[0]),
+			getOKCertResult(revokableChain[2].OCSPServer[0]),
+			getOKCertResult(revokableChain[3].OCSPServer[0]),
+			getOKCertResult(revokableChain[4].OCSPServer[0]),
+			getRootCertResult(),
+		}
+		validateEquivalentCertResults(certResults, expectedCertResults, t)
+	})
+	t.Run("check OCSP with 1 unknown and 1 future revoked cert", func(t *testing.T) {
+		revokedTime := time.Now().Add(time.Hour)
+		// 3rd cert will be unknown, 5th will be future revoked, the rest will be good
+		client := testhelper.MockClient(testChain, []ocsp.ResponseStatus{ocsp.Good, ocsp.Good, ocsp.Unknown, ocsp.Good, ocsp.Revoked, ocsp.Good}, &revokedTime, true)
+		r, err := NewWithOptions(Options{
+			OCSPHTTPClient:   client,
+			CertChainPurpose: purpose.Timestamping,
+		})
+		if err != nil {
+			t.Errorf("Expected successful creation of revocation, but received error: %v", err)
+		}
+		certResults, err := r.ValidateContext(context.Background(), ValidateContextOptions{
+			CertChain:            revokableChain,
+			AuthenticSigningTime: time.Now(),
+		})
+		if err != nil {
+			t.Errorf("Expected CheckStatus to succeed, but got error: %v", err)
+		}
+		expectedCertResults := []*result.CertRevocationResult{
+			getOKCertResult(revokableChain[0].OCSPServer[0]),
+			getOKCertResult(revokableChain[1].OCSPServer[0]),
+			{
+				Result: result.ResultUnknown,
+				ServerResults: []*result.ServerResult{
+					result.NewServerResult(result.ResultUnknown, revokableChain[2].OCSPServer[0], revocationocsp.UnknownStatusError{}),
+				},
+				RevocationMethod: result.RevocationMethodOCSP,
+			},
+			getOKCertResult(revokableChain[3].OCSPServer[0]),
+			getOKCertResult(revokableChain[4].OCSPServer[0]),
+			getRootCertResult(),
+		}
+		validateEquivalentCertResults(certResults, expectedCertResults, t)
+	})
+	t.Run("check OCSP with 1 revoked cert before signing time", func(t *testing.T) {
+		// 3rd cert will be revoked, the rest will be good
+		client := testhelper.MockClient(testChain, []ocsp.ResponseStatus{ocsp.Good, ocsp.Good, ocsp.Revoked, ocsp.Good}, nil, true)
+		r, err := NewWithOptions(Options{
+			OCSPHTTPClient:   client,
+			CertChainPurpose: purpose.Timestamping,
+		})
+		if err != nil {
+			t.Errorf("Expected successful creation of revocation, but received error: %v", err)
+		}
+		certResults, err := r.ValidateContext(context.Background(), ValidateContextOptions{
+			CertChain:            revokableChain,
+			AuthenticSigningTime: time.Now().Add(time.Hour),
+		})
+		if err != nil {
+			t.Errorf("Expected CheckStatus to succeed, but got error: %v", err)
+		}
+		expectedCertResults := []*result.CertRevocationResult{
+			getOKCertResult(revokableChain[0].OCSPServer[0]),
+			getOKCertResult(revokableChain[1].OCSPServer[0]),
+			{
+				Result: result.ResultRevoked,
+				ServerResults: []*result.ServerResult{
+					result.NewServerResult(result.ResultRevoked, revokableChain[2].OCSPServer[0], revocationocsp.RevokedError{}),
+				},
+				RevocationMethod: result.RevocationMethodOCSP,
+			},
+			getOKCertResult(revokableChain[3].OCSPServer[0]),
+			getOKCertResult(revokableChain[4].OCSPServer[0]),
+			getRootCertResult(),
+		}
+		validateEquivalentCertResults(certResults, expectedCertResults, t)
+	})
+	t.Run("check OCSP with 1 revoked cert after zero signing time", func(t *testing.T) {
+		revokedTime := time.Now().Add(time.Hour)
+		// 3rd cert will be revoked, the rest will be good
+		client := testhelper.MockClient(testChain, []ocsp.ResponseStatus{ocsp.Good, ocsp.Good, ocsp.Revoked, ocsp.Good}, &revokedTime, true)
+		if !zeroTime.IsZero() {
+			t.Errorf("exected zeroTime.IsZero() to be true")
+		}
+		r, err := NewWithOptions(Options{
+			OCSPHTTPClient:   client,
+			CertChainPurpose: purpose.Timestamping,
+		})
+		if err != nil {
+			t.Errorf("Expected successful creation of revocation, but received error: %v", err)
+		}
+		certResults, err := r.ValidateContext(context.Background(), ValidateContextOptions{
+			CertChain:            revokableChain,
+			AuthenticSigningTime: time.Now().Add(time.Hour),
+		})
+		if err != nil {
+			t.Errorf("Expected CheckStatus to succeed, but got error: %v", err)
+		}
+		expectedCertResults := []*result.CertRevocationResult{
+			getOKCertResult(revokableChain[0].OCSPServer[0]),
+			getOKCertResult(revokableChain[1].OCSPServer[0]),
+			{
+				Result: result.ResultRevoked,
+				ServerResults: []*result.ServerResult{
+					result.NewServerResult(result.ResultRevoked, revokableChain[2].OCSPServer[0], revocationocsp.RevokedError{}),
+				},
+				RevocationMethod: result.RevocationMethodOCSP,
 			},
 			getOKCertResult(revokableChain[3].OCSPServer[0]),
 			getOKCertResult(revokableChain[4].OCSPServer[0]),
@@ -472,13 +823,13 @@ func TestCheckRevocationErrors(t *testing.T) {
 	expiredLeaf, _ := x509.ParseCertificate(revokableTuples[0].Cert.Raw)
 	expiredLeaf.IsCA = false
 	expiredLeaf.KeyUsage = x509.KeyUsageDigitalSignature
-	expiredLeaf.OCSPServer = []string{"http://example.com/expired_ocsp"}
+	expiredLeaf.OCSPServer = []string{"http://localhost.test/expired_ocsp"}
 	expiredChain := []*x509.Certificate{expiredLeaf, revokableTuples[1].Cert, revokableTuples[2].Cert}
 
 	noHTTPLeaf, _ := x509.ParseCertificate(revokableTuples[0].Cert.Raw)
 	noHTTPLeaf.IsCA = false
 	noHTTPLeaf.KeyUsage = x509.KeyUsageDigitalSignature
-	noHTTPLeaf.OCSPServer = []string{"ldap://ds.example.com:123/chain_ocsp/0"}
+	noHTTPLeaf.OCSPServer = []string{"ldap://ds.localhost.test:123/chain_ocsp/0"}
 	noHTTPChain := []*x509.Certificate{noHTTPLeaf, revokableTuples[1].Cert, revokableTuples[2].Cert}
 
 	backwardsChainErr := result.InvalidChainError{Err: errors.New("leaf certificate with subject \"CN=Notation Test Revokable RSA Chain Cert Root,O=Notary,L=Seattle,ST=WA,C=US\" is self-signed. Certificate chain must not contain self-signed leaf certificate")}
@@ -544,12 +895,14 @@ func TestCheckRevocationErrors(t *testing.T) {
 				ServerResults: []*result.ServerResult{
 					result.NewServerResult(result.ResultUnknown, okChain[0].OCSPServer[0], revocationocsp.TimeoutError{}),
 				},
+				RevocationMethod: result.RevocationMethodOCSP,
 			},
 			{
 				Result: result.ResultUnknown,
 				ServerResults: []*result.ServerResult{
 					result.NewServerResult(result.ResultUnknown, okChain[1].OCSPServer[0], revocationocsp.TimeoutError{}),
 				},
+				RevocationMethod: result.RevocationMethodOCSP,
 			},
 			getRootCertResult(),
 		}
@@ -572,6 +925,7 @@ func TestCheckRevocationErrors(t *testing.T) {
 				ServerResults: []*result.ServerResult{
 					result.NewServerResult(result.ResultUnknown, expiredChain[0].OCSPServer[0], expiredRespErr),
 				},
+				RevocationMethod: result.RevocationMethodOCSP,
 			},
 			getOKCertResult(expiredChain[1].OCSPServer[0]),
 			getRootCertResult(),
@@ -614,6 +968,7 @@ func TestCheckRevocationErrors(t *testing.T) {
 				ServerResults: []*result.ServerResult{
 					result.NewServerResult(result.ResultUnknown, noHTTPChain[0].OCSPServer[0], noHTTPErr),
 				},
+				RevocationMethod: result.RevocationMethodOCSP,
 			},
 			getOKCertResult(noHTTPChain[1].OCSPServer[0]),
 			getRootCertResult(),
@@ -629,7 +984,7 @@ func TestCheckRevocationInvalidChain(t *testing.T) {
 	for i, cert := range misorderedIntermediateChain {
 		if i != (len(misorderedIntermediateChain) - 1) {
 			// Skip root which won't have an OCSP Server
-			cert.OCSPServer[0] = fmt.Sprintf("http://example.com/chain_ocsp/%d", i)
+			cert.OCSPServer[0] = fmt.Sprintf("http://localhost.test/chain_ocsp/%d", i)
 		}
 	}
 
@@ -637,7 +992,7 @@ func TestCheckRevocationInvalidChain(t *testing.T) {
 	for i, cert := range missingIntermediateChain {
 		if i != (len(missingIntermediateChain) - 1) {
 			// Skip root which won't have an OCSP Server
-			cert.OCSPServer[0] = fmt.Sprintf("http://example.com/chain_ocsp/%d", i)
+			cert.OCSPServer[0] = fmt.Sprintf("http://localhost.test/chain_ocsp/%d", i)
 		}
 	}
 
@@ -676,3 +1031,349 @@ func TestCheckRevocationInvalidChain(t *testing.T) {
 		}
 	})
 }
+
+func TestCRL(t *testing.T) {
+	t.Run("CRL check valid", func(t *testing.T) {
+		chain := testhelper.GetRevokableRSAChainWithRevocations(3, false, true)
+
+		fetcher, err := crl.NewHTTPFetcher(&http.Client{
+			Timeout: 5 * time.Second,
+			Transport: &crlRoundTripper{
+				CertChain: chain,
+				Revoked:   false,
+			},
+		})
+		if err != nil {
+			t.Errorf("Expected successful creation of fetcher, but received error: %v", err)
+		}
+
+		revocationClient, err := NewWithOptions(Options{
+			OCSPHTTPClient:   &http.Client{},
+			CRLFetcher:       fetcher,
+			CertChainPurpose: purpose.CodeSigning,
+		})
+		if err != nil {
+			t.Errorf("Expected successful creation of revocation, but received error: %v", err)
+		}
+
+		certResults, err := revocationClient.ValidateContext(context.Background(), ValidateContextOptions{
+			CertChain:            []*x509.Certificate{chain[0].Cert, chain[1].Cert, chain[2].Cert},
+			AuthenticSigningTime: time.Now(),
+		})
+		if err != nil {
+			t.Errorf("Expected CheckStatus to succeed, but got error: %v", err)
+		}
+
+		expectedCertResults := []*result.CertRevocationResult{
+			{
+				Result: result.ResultOK,
+				ServerResults: []*result.ServerResult{{
+					Result: result.ResultOK,
+					Server: "http://localhost.test/chain_crl/0",
+				}},
+				RevocationMethod: result.RevocationMethodCRL,
+			},
+			{
+				Result: result.ResultOK,
+				ServerResults: []*result.ServerResult{{
+					Result: result.ResultOK,
+					Server: "http://localhost.test/chain_crl/1",
+				}},
+				RevocationMethod: result.RevocationMethodCRL,
+			},
+			getRootCertResult(),
+		}
+
+		validateEquivalentCertResults(certResults, expectedCertResults, t)
+	})
+
+	t.Run("CRL check with revoked status", func(t *testing.T) {
+		chain := testhelper.GetRevokableRSAChainWithRevocations(3, false, true)
+
+		fetcher, err := crl.NewHTTPFetcher(&http.Client{
+			Timeout: 5 * time.Second,
+			Transport: &crlRoundTripper{
+				CertChain: chain,
+				Revoked:   true,
+			},
+		})
+		if err != nil {
+			t.Errorf("Expected successful creation of fetcher, but received error: %v", err)
+		}
+
+		revocationClient, err := NewWithOptions(Options{
+			OCSPHTTPClient:   &http.Client{},
+			CRLFetcher:       fetcher,
+			CertChainPurpose: purpose.CodeSigning,
+		})
+		if err != nil {
+			t.Errorf("Expected successful creation of revocation, but received error: %v", err)
+		}
+
+		certResults, err := revocationClient.ValidateContext(context.Background(), ValidateContextOptions{
+			CertChain: []*x509.Certificate{
+				chain[0].Cert, // leaf
+				chain[1].Cert, // intermediate
+				chain[2].Cert, // root
+			},
+			AuthenticSigningTime: time.Now(),
+		})
+		if err != nil {
+			t.Errorf("Expected CheckStatus to succeed, but got error: %v", err)
+		}
+
+		expectedCertResults := []*result.CertRevocationResult{
+			{
+				Result: result.ResultRevoked,
+				ServerResults: []*result.ServerResult{
+					{
+						Result: result.ResultRevoked,
+						Server: "http://localhost.test/chain_crl/0",
+					},
+				},
+				RevocationMethod: result.RevocationMethodCRL,
+			},
+			{
+				Result: result.ResultRevoked,
+				ServerResults: []*result.ServerResult{
+					{
+						Result: result.ResultRevoked,
+						Server: "http://localhost.test/chain_crl/1",
+					},
+				},
+				RevocationMethod: result.RevocationMethodCRL,
+			},
+			getRootCertResult(),
+		}
+
+		validateEquivalentCertResults(certResults, expectedCertResults, t)
+	})
+
+	t.Run("OCSP fallback to CRL", func(t *testing.T) {
+		chain := testhelper.GetRevokableRSAChainWithRevocations(3, true, true)
+		fetcher, err := crl.NewHTTPFetcher(&http.Client{
+			Timeout: 5 * time.Second,
+			Transport: &crlRoundTripper{
+				CertChain: chain,
+				Revoked:   true,
+				FailOCSP:  true,
+			},
+		})
+		if err != nil {
+			t.Errorf("Expected successful creation of fetcher, but received error: %v", err)
+		}
+
+		revocationClient, err := NewWithOptions(Options{
+			OCSPHTTPClient: &http.Client{
+				Transport: &serverErrorTransport{},
+			},
+			CRLFetcher:       fetcher,
+			CertChainPurpose: purpose.CodeSigning,
+		})
+		if err != nil {
+			t.Errorf("Expected successful creation of revocation, but received error: %v", err)
+		}
+
+		certResults, err := revocationClient.ValidateContext(context.Background(), ValidateContextOptions{
+			CertChain: []*x509.Certificate{
+				chain[0].Cert, // leaf
+				chain[1].Cert, // intermediate
+				chain[2].Cert, // root
+			},
+			AuthenticSigningTime: time.Now(),
+		})
+		if err != nil {
+			t.Errorf("Expected CheckStatus to succeed, but got error: %v", err)
+		}
+
+		expectedCertResults := []*result.CertRevocationResult{
+			{
+				Result: result.ResultRevoked,
+				ServerResults: []*result.ServerResult{
+					{
+						Result:           result.ResultUnknown,
+						Server:           "http://localhost.test/chain_ocsp/0",
+						Error:            errors.New("failed to retrieve OCSP: response had status code 500"),
+						RevocationMethod: result.RevocationMethodOCSP,
+					},
+					{
+						Result:           result.ResultRevoked,
+						Server:           "http://localhost.test/chain_crl/0",
+						RevocationMethod: result.RevocationMethodCRL,
+					},
+				},
+				RevocationMethod: result.RevocationMethodOCSPFallbackCRL,
+			},
+			{
+				Result: result.ResultRevoked,
+				ServerResults: []*result.ServerResult{
+					{
+						Result:           result.ResultUnknown,
+						Server:           "http://localhost.test/chain_ocsp/1",
+						Error:            errors.New("failed to retrieve OCSP: response had status code 500"),
+						RevocationMethod: result.RevocationMethodOCSPFallbackCRL,
+					},
+					{
+						Result:           result.ResultRevoked,
+						Server:           "http://localhost.test/chain_crl/1",
+						RevocationMethod: result.RevocationMethodCRL,
+					},
+				},
+				RevocationMethod: result.RevocationMethodOCSPFallbackCRL,
+			},
+			getRootCertResult(),
+		}
+
+		validateEquivalentCertResults(certResults, expectedCertResults, t)
+	})
+}
+
+func TestPanicHandling(t *testing.T) {
+	t.Run("panic in OCSP", func(t *testing.T) {
+		chain := testhelper.GetRevokableRSAChainWithRevocations(2, true, false)
+		client := &http.Client{
+			Transport: panicTransport{},
+		}
+
+		fetcher, err := crl.NewHTTPFetcher(client)
+		if err != nil {
+			t.Errorf("Expected successful creation of fetcher, but received error: %v", err)
+		}
+
+		r, err := NewWithOptions(Options{
+			OCSPHTTPClient:   client,
+			CRLFetcher:       fetcher,
+			CertChainPurpose: purpose.CodeSigning,
+		})
+		if err != nil {
+			t.Errorf("Expected successful creation of revocation, but received error: %v", err)
+		}
+
+		defer func() {
+			if r := recover(); r == nil {
+				t.Error("Expected panic, but got nil")
+			}
+		}()
+		_, _ = r.ValidateContext(context.Background(), ValidateContextOptions{
+			CertChain:            []*x509.Certificate{chain[0].Cert, chain[1].Cert},
+			AuthenticSigningTime: time.Now(),
+		})
+
+	})
+
+	t.Run("panic in CRL", func(t *testing.T) {
+		chain := testhelper.GetRevokableRSAChainWithRevocations(2, false, true)
+		client := &http.Client{
+			Transport: panicTransport{},
+		}
+
+		fetcher, err := crl.NewHTTPFetcher(client)
+		if err != nil {
+			t.Errorf("Expected successful creation of fetcher, but received error: %v", err)
+		}
+
+		r, err := NewWithOptions(Options{
+			OCSPHTTPClient:   client,
+			CRLFetcher:       fetcher,
+			CertChainPurpose: purpose.CodeSigning,
+		})
+		if err != nil {
+			t.Errorf("Expected successful creation of revocation, but received error: %v", err)
+		}
+
+		defer func() {
+			if r := recover(); r == nil {
+				t.Error("Expected panic, but got nil")
+			}
+		}()
+		_, _ = r.ValidateContext(context.Background(), ValidateContextOptions{
+			CertChain:            []*x509.Certificate{chain[0].Cert, chain[1].Cert},
+			AuthenticSigningTime: time.Now(),
+		})
+	})
+}
+
+type crlRoundTripper struct {
+	CertChain []testhelper.RSACertTuple
+	Revoked   bool
+	FailOCSP  bool
+}
+
+func (rt *crlRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	// e.g. ocsp URL: http://localhost.test/chain_ocsp/0
+	// e.g. crl URL: http://localhost.test/chain_crl/0
+	parts := strings.Split(req.URL.Path, "/")
+
+	isOCSP := parts[len(parts)-2] == "chain_ocsp"
+	// fail OCSP
+	if rt.FailOCSP && isOCSP {
+		return nil, errors.New("OCSP failed")
+	}
+
+	// choose the cert suffix based on suffix of request url
+	// e.g. http://localhost.test/chain_crl/0 -> 0
+	i, err := strconv.Atoi(parts[len(parts)-1])
+	if err != nil {
+		return nil, err
+	}
+	if i >= len(rt.CertChain) {
+		return nil, errors.New("invalid index")
+	}
+
+	cert := rt.CertChain[i].Cert
+	crl := &x509.RevocationList{
+		NextUpdate: time.Now().Add(time.Hour),
+		Number:     big.NewInt(20240720),
+	}
+
+	if rt.Revoked {
+		crl.RevokedCertificateEntries = []x509.RevocationListEntry{
+			{
+				SerialNumber:   cert.SerialNumber,
+				RevocationTime: time.Now().Add(-time.Hour),
+			},
+		}
+	}
+
+	issuerCert := rt.CertChain[i+1].Cert
+	issuerKey := rt.CertChain[i+1].PrivateKey
+	crlBytes, err := x509.CreateRevocationList(rand.Reader, crl, issuerCert, issuerKey)
+	if err != nil {
+		return nil, err
+	}
+
+	return &http.Response{
+		StatusCode: http.StatusOK,
+		Body:       io.NopCloser(bytes.NewReader(crlBytes)),
+	}, nil
+}
+
+type panicTransport struct{}
+
+func (t panicTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	panic("panic")
+}
+
+type serverErrorTransport struct{}
+
+func (t serverErrorTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	return &http.Response{
+		StatusCode: http.StatusInternalServerError,
+		Body:       io.NopCloser(bytes.NewReader([]byte{})),
+	}, nil
+}
+
+func TestValidateContext(t *testing.T) {
+	r, err := NewWithOptions(Options{
+		OCSPHTTPClient:   &http.Client{},
+		CertChainPurpose: purpose.CodeSigning,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	expectedErrMsg := "invalid chain: expected chain to be correct and complete: chain does not contain any certificates"
+	_, err = r.ValidateContext(context.Background(), ValidateContextOptions{})
+	if err == nil || err.Error() != expectedErrMsg {
+		t.Fatalf("expected %s, but got %s", expectedErrMsg, err)
+	}
+}

signature/algorithm.go

@@ -14,112 +14,44 @@
 package signature
 
 import (
-	"crypto"
-	"crypto/ecdsa"
-	"crypto/rsa"
 	"crypto/x509"
-	"fmt"
+
+	"github.com/notaryproject/notation-core-go/internal/algorithm"
 )
 
 // Algorithm defines the signature algorithm.
-type Algorithm int
+type Algorithm = algorithm.Algorithm
 
 // Signature algorithms supported by this library.
 //
 // Reference: https://github.com/notaryproject/notaryproject/blob/main/specs/signature-specification.md#algorithm-selection
 const (
-	AlgorithmPS256 Algorithm = 1 + iota // RSASSA-PSS with SHA-256
+	AlgorithmPS256 = algorithm.AlgorithmPS256 // RSASSA-PSS with SHA-256
-	AlgorithmPS384                      // RSASSA-PSS with SHA-384
+	AlgorithmPS384 = algorithm.AlgorithmPS384 // RSASSA-PSS with SHA-384
-	AlgorithmPS512                      // RSASSA-PSS with SHA-512
+	AlgorithmPS512 = algorithm.AlgorithmPS512 // RSASSA-PSS with SHA-512
-	AlgorithmES256                      // ECDSA on secp256r1 with SHA-256
+	AlgorithmES256 = algorithm.AlgorithmES256 // ECDSA on secp256r1 with SHA-256
-	AlgorithmES384                      // ECDSA on secp384r1 with SHA-384
+	AlgorithmES384 = algorithm.AlgorithmES384 // ECDSA on secp384r1 with SHA-384
-	AlgorithmES512                      // ECDSA on secp521r1 with SHA-512
+	AlgorithmES512 = algorithm.AlgorithmES512 // ECDSA on secp521r1 with SHA-512
 )
 
 // KeyType defines the key type.
-type KeyType int
+type KeyType = algorithm.KeyType
 
 const (
-	KeyTypeRSA KeyType = 1 + iota // KeyType RSA
+	KeyTypeRSA = algorithm.KeyTypeRSA // KeyType RSA
-	KeyTypeEC                     // KeyType EC
+	KeyTypeEC  = algorithm.KeyTypeEC  // KeyType EC
 )
 
 // KeySpec defines a key type and size.
-type KeySpec struct {
+type KeySpec = algorithm.KeySpec
-	// KeyType is the type of the key.
-	Type KeyType
-
-	// KeySize is the size of the key in bits.
-	Size int
-}
-
-// Hash returns the hash function of the algorithm.
-func (alg Algorithm) Hash() crypto.Hash {
-	switch alg {
-	case AlgorithmPS256, AlgorithmES256:
-		return crypto.SHA256
-	case AlgorithmPS384, AlgorithmES384:
-		return crypto.SHA384
-	case AlgorithmPS512, AlgorithmES512:
-		return crypto.SHA512
-	}
-	return 0
-}
 
 // ExtractKeySpec extracts KeySpec from the signing certificate.
 func ExtractKeySpec(signingCert *x509.Certificate) (KeySpec, error) {
-	switch key := signingCert.PublicKey.(type) {
+	ks, err := algorithm.ExtractKeySpec(signingCert)
-	case *rsa.PublicKey:
+	if err != nil {
-		switch bitSize := key.Size() << 3; bitSize {
-		case 2048, 3072, 4096:
-			return KeySpec{
-				Type: KeyTypeRSA,
-				Size: bitSize,
-			}, nil
-		default:
 		return KeySpec{}, &UnsupportedSigningKeyError{
-				Msg: fmt.Sprintf("rsa key size %d bits is not supported", bitSize),
+			Msg: err.Error(),
 		}
 	}
-	case *ecdsa.PublicKey:
+	return ks, nil
-		switch bitSize := key.Curve.Params().BitSize; bitSize {
-		case 256, 384, 521:
-			return KeySpec{
-				Type: KeyTypeEC,
-				Size: bitSize,
-			}, nil
-		default:
-			return KeySpec{}, &UnsupportedSigningKeyError{
-				Msg: fmt.Sprintf("ecdsa key size %d bits is not supported", bitSize),
-			}
-		}
-	}
-	return KeySpec{}, &UnsupportedSigningKeyError{
-		Msg: "unsupported public key type",
-	}
-}
-
-// SignatureAlgorithm returns the signing algorithm associated with the KeySpec.
-func (k KeySpec) SignatureAlgorithm() Algorithm {
-	switch k.Type {
-	case KeyTypeEC:
-		switch k.Size {
-		case 256:
-			return AlgorithmES256
-		case 384:
-			return AlgorithmES384
-		case 521:
-			return AlgorithmES512
-		}
-	case KeyTypeRSA:
-		switch k.Size {
-		case 2048:
-			return AlgorithmPS256
-		case 3072:
-			return AlgorithmPS384
-		case 4096:
-			return AlgorithmPS512
-		}
-	}
-	return 0
 }

signature/algorithm_test.go

@@ -14,7 +14,6 @@
 package signature
 
 import (
-	"crypto"
 	"crypto/ecdsa"
 	"crypto/ed25519"
 	"crypto/elliptic"
@@ -28,59 +27,6 @@ import (
 	"github.com/notaryproject/notation-core-go/testhelper"
 )
 
-func TestHash(t *testing.T) {
-	tests := []struct {
-		name   string
-		alg    Algorithm
-		expect crypto.Hash
-	}{
-		{
-			name:   "PS256",
-			alg:    AlgorithmPS256,
-			expect: crypto.SHA256,
-		},
-		{
-			name:   "ES256",
-			alg:    AlgorithmES256,
-			expect: crypto.SHA256,
-		},
-		{
-			name:   "PS384",
-			alg:    AlgorithmPS384,
-			expect: crypto.SHA384,
-		},
-		{
-			name:   "ES384",
-			alg:    AlgorithmES384,
-			expect: crypto.SHA384,
-		},
-		{
-			name:   "PS512",
-			alg:    AlgorithmPS512,
-			expect: crypto.SHA512,
-		},
-		{
-			name:   "ES512",
-			alg:    AlgorithmES512,
-			expect: crypto.SHA512,
-		},
-		{
-			name:   "UnsupportedAlgorithm",
-			alg:    0,
-			expect: 0,
-		},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			hash := tt.alg.Hash()
-			if hash != tt.expect {
-				t.Fatalf("Expected %v, got %v", tt.expect, hash)
-			}
-		})
-	}
-}
-
 func TestExtractKeySpec(t *testing.T) {
 	type testCase struct {
 		name      string
@@ -168,77 +114,3 @@ func TestExtractKeySpec(t *testing.T) {
 		})
 	}
 }
-
-func TestSignatureAlgorithm(t *testing.T) {
-	tests := []struct {
-		name    string
-		keySpec KeySpec
-		expect  Algorithm
-	}{
-		{
-			name: "EC 256",
-			keySpec: KeySpec{
-				Type: KeyTypeEC,
-				Size: 256,
-			},
-			expect: AlgorithmES256,
-		},
-		{
-			name: "EC 384",
-			keySpec: KeySpec{
-				Type: KeyTypeEC,
-				Size: 384,
-			},
-			expect: AlgorithmES384,
-		},
-		{
-			name: "EC 521",
-			keySpec: KeySpec{
-				Type: KeyTypeEC,
-				Size: 521,
-			},
-			expect: AlgorithmES512,
-		},
-		{
-			name: "RSA 2048",
-			keySpec: KeySpec{
-				Type: KeyTypeRSA,
-				Size: 2048,
-			},
-			expect: AlgorithmPS256,
-		},
-		{
-			name: "RSA 3072",
-			keySpec: KeySpec{
-				Type: KeyTypeRSA,
-				Size: 3072,
-			},
-			expect: AlgorithmPS384,
-		},
-		{
-			name: "RSA 4096",
-			keySpec: KeySpec{
-				Type: KeyTypeRSA,
-				Size: 4096,
-			},
-			expect: AlgorithmPS512,
-		},
-		{
-			name: "Unsupported key spec",
-			keySpec: KeySpec{
-				Type: 0,
-				Size: 0,
-			},
-			expect: 0,
-		},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			alg := tt.keySpec.SignatureAlgorithm()
-			if alg != tt.expect {
-				t.Errorf("unexpected signature algorithm: %v, expect: %v", alg, tt.expect)
-			}
-		})
-	}
-}

signature/cose/conformance_test.go

@@ -57,7 +57,7 @@ func TestConformance(t *testing.T) {
 
 // testSign does conformance check on COSE_Sign1_Tagged
 func testSign(t *testing.T, sign1 *sign1) {
-	signRequest, err := getSignReq(sign1)
+	signRequest, err := getSignReq()
 	if err != nil {
 		t.Fatalf("getSignReq() failed. Error = %s", err)
 	}
@@ -90,7 +90,7 @@ func testSign(t *testing.T, sign1 *sign1) {
 // testVerify does conformance check by decoding COSE_Sign1_Tagged object
 // into Sign1Message
 func testVerify(t *testing.T, sign1 *sign1) {
-	signRequest, err := getSignReq(sign1)
+	signRequest, err := getSignReq()
 	if err != nil {
 		t.Fatalf("getSignReq() failed. Error = %s", err)
 	}
@@ -124,7 +124,7 @@ func testVerify(t *testing.T, sign1 *sign1) {
 	verifySignerInfo(&content.SignerInfo, signRequest, t)
 }
 
-func getSignReq(sign1 *sign1) (*signature.SignRequest, error) {
+func getSignReq() (*signature.SignRequest, error) {
 	certs := []*x509.Certificate{testhelper.GetRSALeafCertificate().Cert, testhelper.GetRSARootCertificate().Cert}
 	signer, err := signature.NewLocalSigner(certs, testhelper.GetRSALeafCertificate().PrivateKey)
 	if err != nil {

signature/cose/envelope.go

@@ -24,8 +24,10 @@ import (
 	"time"
 
 	"github.com/fxamacker/cbor/v2"
+	"github.com/notaryproject/notation-core-go/internal/timestamp"
 	"github.com/notaryproject/notation-core-go/signature"
 	"github.com/notaryproject/notation-core-go/signature/internal/base"
+	"github.com/notaryproject/tspclient-go"
 	"github.com/veraison/go-cose"
 )
 
@@ -76,7 +78,7 @@ const (
 // Unprotected Headers
 // https://github.com/notaryproject/notaryproject/blob/cose-envelope/signature-envelope-cose.md
 const (
-	headerLabelTimeStampSignature = "io.cncf.notary.timestampSignature"
+	headerLabelTimestampSignature = "io.cncf.notary.timestampSignature"
 	headerLabelSigningAgent       = "io.cncf.notary.signingAgent"
 )
 
@@ -234,10 +236,26 @@ func (e *envelope) Sign(req *signature.SignRequest) ([]byte, error) {
 		return nil, &signature.InvalidSignRequestError{Msg: err.Error()}
 	}
 
-	// generate unprotected headers of COSE envelope
+	// generate unprotected headers of COSE envelope.
 	generateUnprotectedHeaders(req, signer, msg.Headers.Unprotected)
 
-	// TODO: needs to add headerKeyTimeStampSignature.
+	// timestamping
+	if req.SigningScheme == signature.SigningSchemeX509 && req.Timestamper != nil {
+		hash, err := hashFromCOSEAlgorithm(signer.Algorithm())
+		if err != nil {
+			return nil, &signature.TimestampError{Detail: err}
+		}
+		timestampOpts := tspclient.RequestOptions{
+			Content:       msg.Signature,
+			HashAlgorithm: hash,
+		}
+		timestampToken, err := timestamp.Timestamp(req, timestampOpts)
+		if err != nil {
+			return nil, &signature.TimestampError{Detail: err}
+		}
+		// on success, embed the timestamp token to Unprotected header
+		msg.Headers.Unprotected[headerLabelTimestampSignature] = timestampToken
+	}
 
 	// encode Sign1Message into COSE_Sign1_Tagged object
 	encoded, err := msg.MarshalCBOR()
@@ -368,7 +386,10 @@ func (e *envelope) signerInfo() (*signature.SignerInfo, error) {
 		signerInfo.UnsignedAttributes.SigningAgent = h
 	}
 
-	// TODO: needs to add headerKeyTimeStampSignature.
+	// populate signerInfo.UnsignedAttributes.TimestampSignature
+	if timestamepToken, ok := e.base.Headers.Unprotected[headerLabelTimestampSignature].([]byte); ok {
+		signerInfo.UnsignedAttributes.TimestampSignature = timestamepToken
+	}
 
 	return &signerInfo, nil
 }
@@ -701,3 +722,17 @@ func generateRawProtectedCBORMap(rawProtected cbor.RawMessage) (map[any]cbor.Raw
 
 	return headerMap, nil
 }
+
+// hashFromCOSEAlgorithm maps the cose algorithm supported by go-cose to hash
+func hashFromCOSEAlgorithm(alg cose.Algorithm) (crypto.Hash, error) {
+	switch alg {
+	case cose.AlgorithmPS256, cose.AlgorithmES256:
+		return crypto.SHA256, nil
+	case cose.AlgorithmPS384, cose.AlgorithmES384:
+		return crypto.SHA384, nil
+	case cose.AlgorithmPS512, cose.AlgorithmES512:
+		return crypto.SHA512, nil
+	default:
+		return 0, fmt.Errorf("unsupported cose algorithm %s", alg)
+	}
+}

signature/cose/envelope_test.go

@@ -14,6 +14,7 @@
 package cose
 
 import (
+	"context"
 	"crypto"
 	"crypto/x509"
 	"errors"
@@ -25,11 +26,15 @@ import (
 	"github.com/notaryproject/notation-core-go/signature"
 	"github.com/notaryproject/notation-core-go/signature/internal/signaturetest"
 	"github.com/notaryproject/notation-core-go/testhelper"
+	nx509 "github.com/notaryproject/notation-core-go/x509"
+	"github.com/notaryproject/tspclient-go"
 	"github.com/veraison/go-cose"
 )
 
 const (
 	payloadString = "{\"targetArtifact\":{\"mediaType\":\"application/vnd.oci.image.manifest.v1+json\",\"digest\":\"sha256:73c803930ea3ba1e54bc25c2bdc53edd0284c62ed651fe7b00369da519a3c333\",\"size\":16724,\"annotations\":{\"io.wabbit-networks.buildId\":\"123\"}}}"
+
+	rfc3161TSAurl = "http://timestamp.digicert.com"
 )
 
 var (
@@ -123,6 +128,49 @@ func TestSign(t *testing.T) {
 			}
 		}
 	}
+
+	t.Run("with timestamp countersignature request", func(t *testing.T) {
+		signRequest, err := newSignRequest("notary.x509", signature.KeyTypeRSA, 3072)
+		if err != nil {
+			t.Fatalf("newSignRequest() failed. Error = %s", err)
+		}
+		signRequest.Timestamper, err = tspclient.NewHTTPTimestamper(nil, rfc3161TSAurl)
+		if err != nil {
+			t.Fatal(err)
+		}
+		rootCerts, err := nx509.ReadCertificateFile("../../internal/timestamp/testdata/tsaRootCert.cer")
+		if err != nil || len(rootCerts) == 0 {
+			t.Fatal("failed to read root CA certificate:", err)
+		}
+		rootCert := rootCerts[0]
+		rootCAs := x509.NewCertPool()
+		rootCAs.AddCert(rootCert)
+		signRequest.TSARootCAs = rootCAs
+		encoded, err := env.Sign(signRequest)
+		if err != nil || encoded == nil {
+			t.Fatalf("Sign() failed. Error = %s", err)
+		}
+		content, err := env.Content()
+		if err != nil {
+			t.Fatal(err)
+		}
+		timestampToken := content.SignerInfo.UnsignedAttributes.TimestampSignature
+		if len(timestampToken) == 0 {
+			t.Fatal("expected timestamp token to be present")
+		}
+		signedToken, err := tspclient.ParseSignedToken(timestampToken)
+		if err != nil {
+			t.Fatal(err)
+		}
+		info, err := signedToken.Info()
+		if err != nil {
+			t.Fatal(err)
+		}
+		_, err = info.Validate(content.SignerInfo.Signature)
+		if err != nil {
+			t.Fatal(err)
+		}
+	})
 }
 
 func TestSignErrors(t *testing.T) {
@@ -288,6 +336,26 @@ func TestSignErrors(t *testing.T) {
 			t.Fatalf("Sign() expects error: %v, but got: %v.", expected, err)
 		}
 	})
+
+	t.Run("when invalid tsa url is provided", func(t *testing.T) {
+		signRequest, err := getSignRequest()
+		if err != nil {
+			t.Fatalf("getSignRequest() failed. Error = %v", err)
+		}
+		signRequest.Timestamper = &dummyTimestamper{}
+		expected := errors.New("timestamp: failed to timestamp")
+		encoded, err := env.Sign(signRequest)
+		if !isErrEqual(expected, err) {
+			t.Fatalf("Sign() expects error: %v, but got: %v.", expected, err)
+		}
+		var timestampErr *signature.TimestampError
+		if !errors.As(err, &timestampErr) {
+			t.Fatal("expected signature.TimestampError")
+		}
+		if encoded != nil {
+			t.Fatal("expected nil signature envelope")
+		}
+	})
 }
 
 func TestVerifyErrors(t *testing.T) {
@@ -801,6 +869,44 @@ func TestGenerateExtendedAttributesError(t *testing.T) {
 	}
 }
 
+func TestHashFunc(t *testing.T) {
+	hash, err := hashFromCOSEAlgorithm(cose.AlgorithmPS256)
+	if err != nil || hash.String() != "SHA-256" {
+		t.Fatalf("expected SHA-256, but got %s", hash)
+	}
+
+	hash, err = hashFromCOSEAlgorithm(cose.AlgorithmPS384)
+	if err != nil || hash.String() != "SHA-384" {
+		t.Fatalf("expected SHA-384, but got %s", hash)
+	}
+
+	hash, err = hashFromCOSEAlgorithm(cose.AlgorithmPS512)
+	if err != nil || hash.String() != "SHA-512" {
+		t.Fatalf("expected SHA-512, but got %s", hash)
+	}
+
+	hash, err = hashFromCOSEAlgorithm(cose.AlgorithmES256)
+	if err != nil || hash.String() != "SHA-256" {
+		t.Fatalf("expected SHA-256, but got %s", hash)
+	}
+
+	hash, err = hashFromCOSEAlgorithm(cose.AlgorithmES384)
+	if err != nil || hash.String() != "SHA-384" {
+		t.Fatalf("expected SHA-384, but got %s", hash)
+	}
+
+	hash, err = hashFromCOSEAlgorithm(cose.AlgorithmES512)
+	if err != nil || hash.String() != "SHA-512" {
+		t.Fatalf("expected SHA-512, but got %s", hash)
+	}
+
+	_, err = hashFromCOSEAlgorithm(cose.AlgorithmEd25519)
+	expectedErrMsg := "unsupported cose algorithm EdDSA"
+	if err == nil || err.Error() != expectedErrMsg {
+		t.Fatalf("expected %s, but got %s", expectedErrMsg, err)
+	}
+}
+
 func newSignRequest(signingScheme string, keyType signature.KeyType, size int) (*signature.SignRequest, error) {
 	signer, err := signaturetest.GetTestLocalSigner(keyType, size)
 	if err != nil {
@@ -993,3 +1099,9 @@ func generateTestRawMessage(raw cbor.RawMessage, label string, unmarshalError bo
 
 	return resRaw
 }
+
+type dummyTimestamper tspclient.Timestamp
+
+func (dts *dummyTimestamper) Timestamp(context.Context, *tspclient.Request) (*tspclient.Response, error) {
+	return nil, errors.New("failed to timestamp")
+}

signature/cose/fuzz_test.go

@@ -0,0 +1,33 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cose
+
+import (
+	"testing"
+)
+
+func FuzzSignatureCose(f *testing.F) {
+	f.Fuzz(func(t *testing.T, envelopeBytes []byte, shouldVerify bool) {
+		e, err := ParseEnvelope(envelopeBytes)
+		if err != nil {
+			t.Skip()
+		}
+
+		if shouldVerify {
+			_, _ = e.Verify()
+		} else {
+			_, _ = e.Content()
+		}
+	})
+}

signature/errors.go

@@ -67,7 +67,7 @@ type SignatureAuthenticityError struct{}
 
 // Error returns the default error message.
 func (e *SignatureAuthenticityError) Error() string {
-	return "signature is not produced by a trusted signer"
+	return "the signature's certificate chain does not contain any trusted certificate"
 }
 
 // UnsupportedSigningKeyError is used when a signing key is not supported.
@@ -142,3 +142,28 @@ type DuplicateKeyError struct {
 func (e *DuplicateKeyError) Error() string {
 	return fmt.Sprintf("repeated key: %q exists.", e.Key)
 }
+
+// TimestampError is any error related to RFC3161 Timestamp.
+type TimestampError struct {
+	Msg    string
+	Detail error
+}
+
+// Error returns the formatted error message.
+func (e *TimestampError) Error() string {
+	if e.Msg != "" && e.Detail != nil {
+		return fmt.Sprintf("timestamp: %s. Error: %s", e.Msg, e.Detail.Error())
+	}
+	if e.Msg != "" {
+		return fmt.Sprintf("timestamp: %s", e.Msg)
+	}
+	if e.Detail != nil {
+		return fmt.Sprintf("timestamp: %s", e.Detail.Error())
+	}
+	return "timestamp error"
+}
+
+// Unwrap returns the detail error of e.
+func (e *TimestampError) Unwrap() error {
+	return e.Detail
+}

signature/errors_test.go

@@ -162,7 +162,7 @@ func TestSignatureEnvelopeNotFoundError(t *testing.T) {
 
 func TestSignatureAuthenticityError(t *testing.T) {
 	err := &SignatureAuthenticityError{}
-	expectMsg := "signature is not produced by a trusted signer"
+	expectMsg := "the signature's certificate chain does not contain any trusted certificate"
 
 	if err.Error() != expectMsg {
 		t.Errorf("Expected %v but got %v", expectMsg, err.Error())
@@ -177,3 +177,34 @@ func TestEnvelopeKeyRepeatedError(t *testing.T) {
 		t.Errorf("Expected %v but got %v", expectMsg, err.Error())
 	}
 }
+
+func TestTimestampError(t *testing.T) {
+	err := &TimestampError{Msg: "test error", Detail: errors.New("test inner error")}
+	expectMsg := "timestamp: test error. Error: test inner error"
+	if err.Error() != expectMsg {
+		t.Errorf("Expected %v but got %v", expectMsg, err.Error())
+	}
+
+	err = &TimestampError{Msg: "test error"}
+	expectMsg = "timestamp: test error"
+	if err.Error() != expectMsg {
+		t.Errorf("Expected %v but got %v", expectMsg, err.Error())
+	}
+
+	err = &TimestampError{Detail: errors.New("test inner error")}
+	expectMsg = "timestamp: test inner error"
+	if err.Error() != expectMsg {
+		t.Errorf("Expected %v but got %v", expectMsg, err.Error())
+	}
+	unwrappedErr := err.Unwrap()
+	expectMsg = "test inner error"
+	if unwrappedErr.Error() != expectMsg {
+		t.Errorf("Expected %s but got %s", errMsg, unwrappedErr.Error())
+	}
+
+	err = &TimestampError{}
+	expectMsg = "timestamp error"
+	if err.Error() != expectMsg {
+		t.Errorf("Expected %v but got %v", expectMsg, err.Error())
+	}
+}

signature/internal/base/envelope.go

@@ -53,7 +53,6 @@ func (e *Envelope) Sign(req *signature.SignRequest) ([]byte, error) {
 	if err != nil {
 		return nil, err
 	}
-
 	if err := validateCertificateChain(
 		content.SignerInfo.CertificateChain,
 		&content.SignerInfo.SignedAttributes.SigningTime,
@@ -62,7 +61,9 @@ func (e *Envelope) Sign(req *signature.SignRequest) ([]byte, error) {
 		return nil, err
 	}
 
+	// store the raw signature
 	e.Raw = raw
+
 	return e.Raw, nil
 }
 

signature/internal/base/envelope_test.go

@@ -22,10 +22,12 @@ import (
 
 	"github.com/notaryproject/notation-core-go/signature"
 	"github.com/notaryproject/notation-core-go/testhelper"
+	"github.com/notaryproject/tspclient-go"
 )
 
 var (
 	errMsg              = "error msg"
+	invalidTimestamper  tspclient.Timestamper
 	invalidSigningAgent = "test/1"
 	validSigningAgent   = "test/0"
 	invalidContentType  = "text/plain"
@@ -97,11 +99,33 @@ var (
 		},
 		SigningAgent: invalidSigningAgent,
 	}
+	reqWithInvalidTSAurl = &signature.SignRequest{
+		Payload: signature.Payload{
+			ContentType: validContentType,
+			Content:     validBytes,
+		},
+		SigningTime:   testhelper.GetRSALeafCertificate().Cert.NotBefore,
+		Expiry:        testhelper.GetRSALeafCertificate().Cert.NotAfter,
+		SigningScheme: signiningSchema,
+		Signer: &mockSigner{
+			keySpec: signature.KeySpec{
+				Type: signature.KeyTypeRSA,
+				Size: 3072,
+			},
+			certs: []*x509.Certificate{
+				testhelper.GetRSALeafCertificate().Cert,
+				testhelper.GetRSARootCertificate().Cert,
+			},
+		},
+		SigningAgent: validSigningAgent,
+		Timestamper:  invalidTimestamper,
+	}
 )
 
 func init() {
 	time08_02, _ = time.Parse(timeLayout, "2020-08-02")
 	time08_03, _ = time.Parse(timeLayout, "2020-08-03")
+	invalidTimestamper, _ = tspclient.NewHTTPTimestamper(nil, "invalid")
 }
 
 // Mock an internal envelope that implements signature.Envelope.
@@ -109,6 +133,7 @@ type mockEnvelope struct {
 	payload       *signature.Payload
 	signerInfo    *signature.SignerInfo
 	content       *signature.EnvelopeContent
+	failTimestamp bool
 	failVerify    bool
 }
 
@@ -118,6 +143,9 @@ func (e mockEnvelope) Sign(req *signature.SignRequest) ([]byte, error) {
 	case invalidSigningAgent:
 		return nil, errors.New(errMsg)
 	case validSigningAgent:
+		if e.failTimestamp {
+			return validBytes, &signature.TimestampError{}
+		}
 		return validBytes, nil
 	}
 	return nil, nil
@@ -234,6 +262,21 @@ func TestSign(t *testing.T) {
 			expect:    validBytes,
 			expectErr: false,
 		},
+		{
+			name: "failed to timestamp",
+			req:  reqWithInvalidTSAurl,
+			env: &Envelope{
+				Raw: validBytes,
+				Envelope: &mockEnvelope{
+					content: &signature.EnvelopeContent{
+						SignerInfo: *validSignerInfo,
+					},
+					failTimestamp: true,
+				},
+			},
+			expect:    nil,
+			expectErr: true,
+		},
 	}
 
 	for _, tt := range tests {
@@ -246,6 +289,17 @@ func TestSign(t *testing.T) {
 			if !reflect.DeepEqual(sig, tt.expect) {
 				t.Errorf("expect %+v, got %+v", tt.expect, sig)
 			}
+
+			if tt.name == "failed to timestamp" {
+				var timestampErr *signature.TimestampError
+				if !errors.As(err, &timestampErr) {
+					t.Fatal("expecting error to be signature.TimestampError")
+				}
+				expectedErrMsg := "timestamp error"
+				if timestampErr.Error() != expectedErrMsg {
+					t.Fatalf("expected error %s, but got %v", expectedErrMsg, err)
+				}
+			}
 		})
 	}
 }

signature/jws/envelope.go

@@ -20,8 +20,10 @@ import (
 	"fmt"
 
 	"github.com/golang-jwt/jwt/v4"
+	"github.com/notaryproject/notation-core-go/internal/timestamp"
 	"github.com/notaryproject/notation-core-go/signature"
 	"github.com/notaryproject/notation-core-go/signature/internal/base"
+	"github.com/notaryproject/tspclient-go"
 )
 
 // MediaTypeEnvelope defines the media type name of JWS envelope.
@@ -91,11 +93,17 @@ func (e *envelope) Sign(req *signature.SignRequest) ([]byte, error) {
 		return nil, &signature.InvalidSignatureError{Msg: err.Error()}
 	}
 
+	// timestamping
+	if err := timestampJWS(env, req, signedAttrs[headerKeySigningScheme].(string)); err != nil {
+		return nil, err
+	}
+
 	encoded, err := json.Marshal(env)
 	if err != nil {
 		return nil, &signature.InvalidSignatureError{Msg: err.Error()}
 	}
 	e.base = env
+
 	return encoded, nil
 }
 
@@ -220,3 +228,34 @@ func sign(payload jwt.MapClaims, headers map[string]interface{}, method signingM
 	}
 	return compact, certs, nil
 }
+
+// timestampJWS timestamps a JWS envelope
+func timestampJWS(env *jwsEnvelope, req *signature.SignRequest, signingScheme string) error {
+	if signingScheme != string(signature.SigningSchemeX509) || req.Timestamper == nil {
+		return nil
+	}
+	primitiveSignature, err := base64.RawURLEncoding.DecodeString(env.Signature)
+	if err != nil {
+		return &signature.TimestampError{Detail: err}
+	}
+	ks, err := req.Signer.KeySpec()
+	if err != nil {
+		return &signature.TimestampError{Detail: err}
+	}
+	hash := ks.SignatureAlgorithm().Hash()
+	if hash == 0 {
+		return &signature.TimestampError{Msg: fmt.Sprintf("got hash value 0 from key spec %+v", ks)}
+	}
+	timestampOpts := tspclient.RequestOptions{
+		Content:       primitiveSignature,
+		HashAlgorithm: hash,
+	}
+	timestampToken, err := timestamp.Timestamp(req, timestampOpts)
+	if err != nil {
+		return &signature.TimestampError{Detail: err}
+	}
+
+	// on success, embed the timestamp token to TimestampSignature
+	env.Header.TimestampSignature = timestampToken
+	return nil
+}

signature/jws/envelope_test.go

@@ -14,6 +14,7 @@
 package jws
 
 import (
+	"context"
 	"crypto"
 	"crypto/ecdsa"
 	"crypto/rand"
@@ -32,8 +33,12 @@ import (
 	"github.com/notaryproject/notation-core-go/signature"
 	"github.com/notaryproject/notation-core-go/signature/internal/signaturetest"
 	"github.com/notaryproject/notation-core-go/testhelper"
+	nx509 "github.com/notaryproject/notation-core-go/x509"
+	"github.com/notaryproject/tspclient-go"
 )
 
+const rfc3161TSAurl = "http://timestamp.digicert.com"
+
 // remoteMockSigner is used to mock remote signer
 type remoteMockSigner struct {
 	privateKey crypto.PrivateKey
@@ -226,8 +231,8 @@ func TestNewEnvelope(t *testing.T) {
 	}
 }
 
-// Test the same key exists both in extended signed attributes and protected header
 func TestSignFailed(t *testing.T) {
+	// Test the same key exists both in extended signed attributes and protected header
 	t.Run("extended attribute conflict with protected header keys", func(t *testing.T) {
 		_, err := getEncodedMessage(signature.SigningSchemeX509, true, extSignedAttrRepeated)
 		checkErrorEqual(t, "attribute key:cty repeated", err.Error())
@@ -253,6 +258,29 @@ func TestSignFailed(t *testing.T) {
 		_, err = e.Sign(signReq)
 		checkErrorEqual(t, `signature algorithm "#0" is not supported`, err.Error())
 	})
+
+	t.Run("invalid tsa url", func(t *testing.T) {
+		env := envelope{}
+		signer, err := signaturetest.GetTestLocalSigner(signature.KeyTypeRSA, 3072)
+		checkNoError(t, err)
+
+		signReq, err := getSignReq(signature.SigningSchemeX509, signer, nil)
+		checkNoError(t, err)
+
+		signReq.Timestamper = &dummyTimestamper{}
+		expected := errors.New("timestamp: failed to timestamp")
+		encoded, err := env.Sign(signReq)
+		if !isErrEqual(expected, err) {
+			t.Fatalf("Sign() expects error: %v, but got: %v.", expected, err)
+		}
+		var timestampErr *signature.TimestampError
+		if !errors.As(err, &timestampErr) {
+			t.Fatal("expected signature.TimestampError")
+		}
+		if encoded != nil {
+			t.Fatal("expected nil signature envelope")
+		}
+	})
 }
 
 func TestSigningScheme(t *testing.T) {
@@ -302,6 +330,52 @@ func TestSignVerify(t *testing.T) {
 	}
 }
 
+func TestSignWithTimestamp(t *testing.T) {
+	signer, err := signaturetest.GetTestLocalSigner(signature.KeyTypeRSA, 3072)
+	checkNoError(t, err)
+
+	signReq, err := getSignReq(signature.SigningSchemeX509, signer, nil)
+	checkNoError(t, err)
+
+	signReq.Timestamper, err = tspclient.NewHTTPTimestamper(nil, rfc3161TSAurl)
+	if err != nil {
+		t.Fatal(err)
+	}
+	rootCerts, err := nx509.ReadCertificateFile("../../internal/timestamp/testdata/tsaRootCert.cer")
+	if err != nil || len(rootCerts) == 0 {
+		t.Fatal("failed to read root CA certificate:", err)
+	}
+	rootCert := rootCerts[0]
+	rootCAs := x509.NewCertPool()
+	rootCAs.AddCert(rootCert)
+	signReq.TSARootCAs = rootCAs
+	env := envelope{}
+	encoded, err := env.Sign(signReq)
+	if err != nil || encoded == nil {
+		t.Fatalf("Sign() failed. Error = %s", err)
+	}
+	content, err := env.Content()
+	if err != nil {
+		t.Fatal(err)
+	}
+	timestampToken := content.SignerInfo.UnsignedAttributes.TimestampSignature
+	if len(timestampToken) == 0 {
+		t.Fatal("expected timestamp token to be present")
+	}
+	signedToken, err := tspclient.ParseSignedToken(timestampToken)
+	if err != nil {
+		t.Fatal(err)
+	}
+	info, err := signedToken.Info()
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, err = info.Validate(content.SignerInfo.Signature)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
 func TestVerify(t *testing.T) {
 	t.Run("break json format", func(t *testing.T) {
 		encoded, err := getEncodedMessage(signature.SigningSchemeX509, true, extSignedAttr)
@@ -601,3 +675,19 @@ func TestEmptyEnvelope(t *testing.T) {
 		}
 	})
 }
+
+func isErrEqual(wanted, got error) bool {
+	if wanted == nil && got == nil {
+		return true
+	}
+	if wanted != nil && got != nil {
+		return wanted.Error() == got.Error()
+	}
+	return false
+}
+
+type dummyTimestamper tspclient.Timestamp
+
+func (dts *dummyTimestamper) Timestamp(context.Context, *tspclient.Request) (*tspclient.Response, error) {
+	return nil, errors.New("failed to timestamp")
+}

signature/jws/fuzz_test.go

@@ -0,0 +1,33 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package jws
+
+import (
+	"testing"
+)
+
+func FuzzSignatureJws(f *testing.F) {
+	f.Fuzz(func(t *testing.T, envelopeBytes []byte, shouldVerify bool) {
+		e, err := ParseEnvelope(envelopeBytes)
+		if err != nil {
+			t.Skip()
+		}
+
+		if shouldVerify {
+			_, _ = e.Verify()
+		} else {
+			_, _ = e.Content()
+		}
+	})
+}

signature/jws/types.go

@@ -73,7 +73,7 @@ type jwsProtectedHeader struct {
 
 // jwsUnprotectedHeader contains the set of unprotected headers.
 type jwsUnprotectedHeader struct {
-	// RFC3161 time stamp token Base64-encoded.
+	// RFC3161 timestamp token Base64-encoded.
 	TimestampSignature []byte `json:"io.cncf.notary.timestampSignature,omitempty"`
 
 	// List of X.509 Base64-DER-encoded certificates

signature/signer.go

@@ -122,22 +122,21 @@ func (s *localSigner) PrivateKey() crypto.PrivateKey {
 	return s.key
 }
 
-// VerifyAuthenticity verifies the certificate chain in the given SignerInfo
+// VerifyAuthenticity iterates the certificate chain in signerInfo, for each
-// with one of the trusted certificates and returns a certificate that matches
+// certificate in the chain, it checks if the certificate matches with one of
-// with one of the certificates in the SignerInfo.
+// the trusted certificates in trustedCerts. It returns the first matching
+// certificate. If no match is found, it returns an error.
 //
 // Reference: https://github.com/notaryproject/notaryproject/blob/main/specs/trust-store-trust-policy.md#steps
 func VerifyAuthenticity(signerInfo *SignerInfo, trustedCerts []*x509.Certificate) (*x509.Certificate, error) {
 	if len(trustedCerts) == 0 {
 		return nil, &InvalidArgumentError{Param: "trustedCerts"}
 	}
-
 	if signerInfo == nil {
 		return nil, &InvalidArgumentError{Param: "signerInfo"}
 	}
-
-	for _, trust := range trustedCerts {
 	for _, cert := range signerInfo.CertificateChain {
+		for _, trust := range trustedCerts {
 			if trust.Equal(cert) {
 				return trust, nil
 			}

signature/types.go

@@ -14,9 +14,14 @@
 package signature
 
 import (
+	"context"
 	"crypto/x509"
 	"errors"
+	"fmt"
 	"time"
+
+	"github.com/notaryproject/notation-core-go/revocation"
+	"github.com/notaryproject/tspclient-go"
 )
 
 // SignatureMediaType list the supported media-type for signatures.
@@ -101,6 +106,46 @@ type SignRequest struct {
 
 	// SigningScheme defines the Notary Project Signing Scheme used by the signature.
 	SigningScheme SigningScheme
+
+	// Timestamper denotes the timestamper for RFC 3161 timestamping
+	Timestamper tspclient.Timestamper
+
+	// TSARootCAs is the set of caller trusted TSA root certificates
+	TSARootCAs *x509.CertPool
+
+	// TSARevocationValidator is used for timestamping certificate
+	// chain revocation check after signing.
+	// When present, only used when timestamping is performed.
+	TSARevocationValidator revocation.Validator
+
+	// ctx is the caller context. It should only be modified via WithContext.
+	// It is unexported to prevent people from using Context wrong
+	// and mutating the contexts held by callers of the same request.
+	ctx context.Context
+}
+
+// Context returns the SignRequest's context. To change the context, use
+// [SignRequest.WithContext].
+//
+// The returned context is always non-nil; it defaults to the
+// background context.
+func (r *SignRequest) Context() context.Context {
+	if r.ctx != nil {
+		return r.ctx
+	}
+	return context.Background()
+}
+
+// WithContext returns a shallow copy of r with its context changed
+// to ctx. The provided ctx must be non-nil.
+func (r *SignRequest) WithContext(ctx context.Context) *SignRequest {
+	if ctx == nil {
+		panic("nil context")
+	}
+	r2 := new(SignRequest)
+	*r2 = *r
+	r2.ctx = ctx
+	return r2
 }
 
 // EnvelopeContent represents a combination of payload to be signed and a parsed
@@ -159,17 +204,21 @@ func (signerInfo *SignerInfo) ExtendedAttribute(key string) (Attribute, error) {
 	return Attribute{}, errors.New("key not in ExtendedAttributes")
 }
 
-// AuthenticSigningTime returns the authentic signing time
+// AuthenticSigningTime returns the authentic signing time under signing scheme
+// notary.x509.signingAuthority.
+// For signing scheme notary.x509, since it only supports authentic timestamp,
+// an error is returned.
+//
+// Reference: https://github.com/notaryproject/specifications/blob/3b0743cd9bb99faee60600dc31d706149775fd49/specs/signature-specification.md#signing-time--authentic-signing-time
 func (signerInfo *SignerInfo) AuthenticSigningTime() (time.Time, error) {
-	switch signerInfo.SignedAttributes.SigningScheme {
+	switch signingScheme := signerInfo.SignedAttributes.SigningScheme; signingScheme {
 	case SigningSchemeX509SigningAuthority:
-		return signerInfo.SignedAttributes.SigningTime, nil
+		signingTime := signerInfo.SignedAttributes.SigningTime
-	case SigningSchemeX509:
+		if signingTime.IsZero() {
-		if len(signerInfo.UnsignedAttributes.TimestampSignature) > 0 {
+			return time.Time{}, fmt.Errorf("authentic signing time must be present under signing scheme %q", signingScheme)
-			// TODO: Add TSA support for AutheticSigningTime
-			// https://github.com/notaryproject/notation-core-go/issues/38
-			return time.Time{}, errors.New("TSA checking has not been implemented")
 		}
+		return signingTime, nil
+	default:
+		return time.Time{}, fmt.Errorf("authentic signing time not supported under signing scheme %q", signingScheme)
 	}
-	return time.Time{}, errors.New("authenticSigningTime not found")
 }

signature/types_test.go

@@ -0,0 +1,93 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package signature
+
+import (
+	"context"
+	"fmt"
+	"testing"
+	"time"
+)
+
+func TestSignRequestContext(t *testing.T) {
+	r := &SignRequest{
+		ctx: context.WithValue(context.Background(), "k1", "v1"),
+	}
+
+	ctx := r.Context()
+	if ctx.Value("k1") != "v1" {
+		t.Fatal("expected k1:v1 in ctx")
+	}
+
+	r = &SignRequest{}
+	ctx = r.Context()
+	if fmt.Sprint(ctx) != "context.Background" {
+		t.Fatal("expected context.Background")
+	}
+}
+
+func TestSignRequestWithContext(t *testing.T) {
+	r := &SignRequest{}
+	ctx := context.WithValue(context.Background(), "k1", "v1")
+	r = r.WithContext(ctx)
+	if r.ctx.Value("k1") != "v1" {
+		t.Fatal("expected k1:v1 in request ctx")
+	}
+
+	defer func() {
+		if rc := recover(); rc == nil {
+			t.Errorf("expected to be panic")
+		}
+	}()
+	r.WithContext(nil) // should panic
+}
+
+func TestAuthenticSigningTime(t *testing.T) {
+	testTime := time.Now()
+	signerInfo := SignerInfo{
+		SignedAttributes: SignedAttributes{
+			SigningScheme: "notary.x509.signingAuthority",
+			SigningTime:   testTime,
+		},
+	}
+	authenticSigningTime, err := signerInfo.AuthenticSigningTime()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !authenticSigningTime.Equal(testTime) {
+		t.Fatalf("expected %s, but got %s", testTime, authenticSigningTime)
+	}
+
+	signerInfo = SignerInfo{
+		SignedAttributes: SignedAttributes{
+			SigningScheme: "notary.x509.signingAuthority",
+		},
+	}
+	expectedErrMsg := "authentic signing time must be present under signing scheme \"notary.x509.signingAuthority\""
+	_, err = signerInfo.AuthenticSigningTime()
+	if err == nil || err.Error() != expectedErrMsg {
+		t.Fatalf("expected %s, but got %s", expectedErrMsg, err)
+	}
+
+	signerInfo = SignerInfo{
+		SignedAttributes: SignedAttributes{
+			SigningScheme: "notary.x509",
+		},
+	}
+	expectedErrMsg = "authentic signing time not supported under signing scheme \"notary.x509\""
+	_, err = signerInfo.AuthenticSigningTime()
+	if err == nil || err.Error() != expectedErrMsg {
+		t.Fatalf("expected %s, but got %s", expectedErrMsg, err)
+	}
+}

testhelper/certificatetest.go

@@ -22,12 +22,15 @@ import (
 	"crypto/rsa"
 	"crypto/x509"
 	"crypto/x509/pkix"
+	"encoding/asn1"
 	"fmt"
 	"math/big"
 	mrand "math/rand"
 	"strconv"
 	"sync"
 	"time"
+
+	"github.com/notaryproject/notation-core-go/internal/oid"
 )
 
 var (
@@ -72,16 +75,46 @@ func GetRevokableRSALeafCertificate() RSACertTuple {
 	return revokableRSALeaf
 }
 
+// GetRevokableRSAChainWithRevocations returns a certificate chain with OCSP
+// and CRL enabled for revocation checks.
+func GetRevokableRSAChainWithRevocations(size int, enabledOCSP, enabledCRL bool) []RSACertTuple {
+	setupCertificates()
+	chain := make([]RSACertTuple, size)
+	chain[size-1] = getRevokableRSARootChainCertTuple("Notation Test Revokable RSA Chain Cert Root", size-1, enabledCRL)
+	for i := size - 2; i > 0; i-- {
+		chain[i] = getRevokableRSAChainCertTuple(fmt.Sprintf("Notation Test Revokable RSA Chain Cert %d", size-i), &chain[i+1], i, enabledOCSP, enabledCRL)
+	}
+	if size > 1 {
+		chain[0] = getRevokableRSALeafChainCertTuple(fmt.Sprintf("Notation Test Revokable RSA Chain Cert %d", size), &chain[1], 0, true, false, enabledOCSP, enabledCRL)
+	}
+	return chain
+}
+
 // GetRevokableRSAChain returns a chain of certificates that specify a local OCSP server signed using RSA algorithm
 func GetRevokableRSAChain(size int) []RSACertTuple {
 	setupCertificates()
 	chain := make([]RSACertTuple, size)
-	chain[size-1] = getRevokableRSARootChainCertTuple("Notation Test Revokable RSA Chain Cert Root", size-1)
+	chain[size-1] = getRevokableRSARootChainCertTuple("Notation Test Revokable RSA Chain Cert Root", size-1, false)
 	for i := size - 2; i > 0; i-- {
-		chain[i] = getRevokableRSAChainCertTuple(fmt.Sprintf("Notation Test Revokable RSA Chain Cert %d", size-i), &chain[i+1], i)
+		chain[i] = getRevokableRSAChainCertTuple(fmt.Sprintf("Notation Test Revokable RSA Chain Cert %d", size-i), &chain[i+1], i, true, false)
 	}
 	if size > 1 {
-		chain[0] = getRevokableRSALeafChainCertTuple(fmt.Sprintf("Notation Test Revokable RSA Chain Cert %d", size), &chain[1], 0)
+		chain[0] = getRevokableRSALeafChainCertTuple(fmt.Sprintf("Notation Test Revokable RSA Chain Cert %d", size), &chain[1], 0, true, false, true, false)
+	}
+	return chain
+}
+
+// GetRevokableRSATimestampChain returns a chain of certificates that specify a local OCSP server signed using RSA algorithm.
+// The leaf certificate is a timestamp certificate.
+func GetRevokableRSATimestampChain(size int) []RSACertTuple {
+	setupCertificates()
+	chain := make([]RSACertTuple, size)
+	chain[size-1] = getRevokableRSARootChainCertTuple("Notation Test Revokable RSA Chain Cert Root", size-1, false)
+	for i := size - 2; i > 0; i-- {
+		chain[i] = getRevokableRSAChainCertTuple(fmt.Sprintf("Notation Test Revokable RSA Chain Cert %d", size-i), &chain[i+1], i, true, false)
+	}
+	if size > 1 {
+		chain[0] = getRevokableRSALeafChainCertTuple(fmt.Sprintf("Notation Test Revokable RSA Chain Cert %d", size), &chain[1], 0, false, true, true, false)
 	}
 	return chain
 }
@@ -148,42 +181,56 @@ func getRSACertTuple(cn string, issuer *RSACertTuple) RSACertTuple {
 }
 
 func getRevokableRSACertTuple(cn string, issuer *RSACertTuple) RSACertTuple {
-	template := getCertTemplate(issuer == nil, true, cn)
+	template := getCertTemplate(issuer == nil, true, false, cn)
-	template.OCSPServer = []string{"http://example.com/ocsp"}
+	template.OCSPServer = []string{"http://localhost.test/ocsp"}
 	return getRSACertTupleWithTemplate(template, issuer.PrivateKey, issuer)
 }
 
-func getRevokableRSAChainCertTuple(cn string, previous *RSACertTuple, index int) RSACertTuple {
+func getRevokableRSAChainCertTuple(cn string, previous *RSACertTuple, index int, enabledOCSP, enabledCRL bool) RSACertTuple {
-	template := getCertTemplate(previous == nil, true, cn)
+	template := getCertTemplate(previous == nil, true, false, cn)
 	template.BasicConstraintsValid = true
 	template.IsCA = true
 	template.KeyUsage = x509.KeyUsageCertSign
-	template.OCSPServer = []string{fmt.Sprintf("http://example.com/chain_ocsp/%d", index)}
+	if enabledOCSP {
+		template.OCSPServer = []string{fmt.Sprintf("http://localhost.test/chain_ocsp/%d", index)}
+	}
+	if enabledCRL {
+		template.KeyUsage |= x509.KeyUsageCRLSign
+		template.CRLDistributionPoints = []string{fmt.Sprintf("http://localhost.test/chain_crl/%d", index)}
+	}
 	return getRSACertTupleWithTemplate(template, previous.PrivateKey, previous)
 }
 
-func getRevokableRSARootChainCertTuple(cn string, pathLen int) RSACertTuple {
+func getRevokableRSARootChainCertTuple(cn string, pathLen int, enabledCRL bool) RSACertTuple {
 	pk, _ := rsa.GenerateKey(rand.Reader, 3072)
-	template := getCertTemplate(true, true, cn)
+	template := getCertTemplate(true, true, false, cn)
 	template.BasicConstraintsValid = true
 	template.IsCA = true
 	template.KeyUsage = x509.KeyUsageCertSign
+	if enabledCRL {
+		template.KeyUsage |= x509.KeyUsageCRLSign
+	}
 	template.MaxPathLen = pathLen
 	return getRSACertTupleWithTemplate(template, pk, nil)
 }
 
-func getRevokableRSALeafChainCertTuple(cn string, issuer *RSACertTuple, index int) RSACertTuple {
+func getRevokableRSALeafChainCertTuple(cn string, issuer *RSACertTuple, index int, codesign, timestamp, enabledOCSP, enabledCRL bool) RSACertTuple {
-	template := getCertTemplate(false, true, cn)
+	template := getCertTemplate(false, codesign, timestamp, cn)
 	template.BasicConstraintsValid = true
 	template.IsCA = false
 	template.KeyUsage = x509.KeyUsageDigitalSignature
-	template.OCSPServer = []string{fmt.Sprintf("http://example.com/chain_ocsp/%d", index)}
+	if enabledOCSP {
+		template.OCSPServer = []string{fmt.Sprintf("http://localhost.test/chain_ocsp/%d", index)}
+	}
+	if enabledCRL {
+		template.CRLDistributionPoints = []string{fmt.Sprintf("http://localhost.test/chain_crl/%d", index)}
+	}
 	return getRSACertTupleWithTemplate(template, issuer.PrivateKey, issuer)
 }
 
 func getRSACertWithoutEKUTuple(cn string, issuer *RSACertTuple) RSACertTuple {
 	pk, _ := rsa.GenerateKey(rand.Reader, 3072)
-	template := getCertTemplate(issuer == nil, false, cn)
+	template := getCertTemplate(issuer == nil, false, false, cn)
 	return getRSACertTupleWithTemplate(template, pk, issuer)
 }
 
@@ -200,18 +247,18 @@ func getECCertTuple(cn string, issuer *ECCertTuple) ECCertTuple {
 func GetRSASelfSignedSigningCertTuple(cn string) RSACertTuple {
 	// Even though we are creating self-signed root, we are using false for 'isRoot' to not
 	// add root CA's basic constraint, KU and EKU.
-	template := getCertTemplate(false, true, cn)
+	template := getCertTemplate(false, true, false, cn)
 	privKey, _ := rsa.GenerateKey(rand.Reader, 3072)
 	return getRSACertTupleWithTemplate(template, privKey, nil)
 }
 
 func GetRSACertTupleWithPK(privKey *rsa.PrivateKey, cn string, issuer *RSACertTuple) RSACertTuple {
-	template := getCertTemplate(issuer == nil, true, cn)
+	template := getCertTemplate(issuer == nil, true, false, cn)
 	return getRSACertTupleWithTemplate(template, privKey, issuer)
 }
 
 func GetRSASelfSignedCertTupleWithPK(privKey *rsa.PrivateKey, cn string) RSACertTuple {
-	template := getCertTemplate(false, true, cn)
+	template := getCertTemplate(false, true, false, cn)
 	return getRSACertTupleWithTemplate(template, privKey, nil)
 }
 
@@ -231,7 +278,7 @@ func getRSACertTupleWithTemplate(template *x509.Certificate, privKey *rsa.Privat
 }
 
 func GetECDSACertTupleWithPK(privKey *ecdsa.PrivateKey, cn string, issuer *ECCertTuple) ECCertTuple {
-	template := getCertTemplate(issuer == nil, true, cn)
+	template := getCertTemplate(issuer == nil, true, false, cn)
 
 	var certBytes []byte
 	if issuer != nil {
@@ -247,7 +294,7 @@ func GetECDSACertTupleWithPK(privKey *ecdsa.PrivateKey, cn string, issuer *ECCer
 	}
 }
 
-func getCertTemplate(isRoot bool, setCodeSignEKU bool, cn string) *x509.Certificate {
+func getCertTemplate(isRoot bool, setCodeSignEKU, setTimestampEKU bool, cn string) *x509.Certificate {
 	template := &x509.Certificate{
 		Subject: pkix.Name{
 			Organization: []string{"Notary"},
@@ -262,6 +309,15 @@ func getCertTemplate(isRoot bool, setCodeSignEKU bool, cn string) *x509.Certific
 
 	if setCodeSignEKU {
 		template.ExtKeyUsage = []x509.ExtKeyUsage{x509.ExtKeyUsageCodeSigning}
+	} else if setTimestampEKU {
+		ekuValue, _ := asn1.Marshal([]asn1.ObjectIdentifier{oid.Timestamping})
+		template.ExtraExtensions = []pkix.Extension{
+			{
+				Id:       oid.ExtKeyUsage,
+				Critical: true,
+				Value:    ekuValue,
+			},
+		}
 	}
 
 	if isRoot {
@@ -275,7 +331,6 @@ func getCertTemplate(isRoot bool, setCodeSignEKU bool, cn string) *x509.Certific
 		template.SerialNumber = big.NewInt(int64(mrand.Intn(200)))
 		template.NotAfter = time.Now().AddDate(0, 0, 1)
 	}
-
 	return template
 }
 

x509/cert_validations.go

@@ -1,301 +0,0 @@
-// Copyright The Notary Project Authors.
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-// http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package x509
-
-import (
-	"bytes"
-	"crypto/ecdsa"
-	"crypto/rsa"
-	"crypto/x509"
-	"errors"
-	"fmt"
-	"strings"
-	"time"
-)
-
-// ValidateCodeSigningCertChain takes an ordered code-signing certificate chain
-// and validates issuance from leaf to root
-// Validates certificates according to this spec:
-// https://github.com/notaryproject/notaryproject/blob/main/specs/signature-specification.md#certificate-requirements
-func ValidateCodeSigningCertChain(certChain []*x509.Certificate, signingTime *time.Time) error {
-	return validateCertChain(certChain, 0, signingTime)
-}
-
-// ValidateTimeStampingCertChain takes an ordered time-stamping certificate
-// chain and validates issuance from leaf to root
-// Validates certificates according to this spec:
-// https://github.com/notaryproject/notaryproject/blob/main/specs/signature-specification.md#certificate-requirements
-func ValidateTimeStampingCertChain(certChain []*x509.Certificate, signingTime *time.Time) error {
-	return validateCertChain(certChain, x509.ExtKeyUsageTimeStamping, signingTime)
-}
-
-func validateCertChain(certChain []*x509.Certificate, expectedLeafEku x509.ExtKeyUsage, signingTime *time.Time) error {
-	if len(certChain) < 1 {
-		return errors.New("certificate chain must contain at least one certificate")
-	}
-
-	// For self-signed signing certificate (not a CA)
-	if len(certChain) == 1 {
-		cert := certChain[0]
-		if signingTime != nil && (signingTime.Before(cert.NotBefore) || signingTime.After(cert.NotAfter)) {
-			return fmt.Errorf("certificate with subject %q was not valid at signing time of %s", cert.Subject, signingTime.UTC())
-		}
-		if err := cert.CheckSignature(cert.SignatureAlgorithm, cert.RawTBSCertificate, cert.Signature); err != nil {
-			return fmt.Errorf("invalid self-signed certificate. subject: %q. Error: %w", cert.Subject, err)
-		}
-		if err := validateLeafCertificate(cert, expectedLeafEku); err != nil {
-			return fmt.Errorf("invalid self-signed certificate. Error: %w", err)
-		}
-		return nil
-	}
-
-	for i, cert := range certChain {
-		if signingTime != nil && (signingTime.Before(cert.NotBefore) || signingTime.After(cert.NotAfter)) {
-			return fmt.Errorf("certificate with subject %q was not valid at signing time of %s", cert.Subject, signingTime.UTC())
-		}
-		if i == len(certChain)-1 {
-			selfSigned, selfSignedError := isSelfSigned(cert)
-			if selfSignedError != nil {
-				return fmt.Errorf("root certificate with subject %q is invalid or not self-signed. Certificate chain must end with a valid self-signed root certificate. Error: %v", cert.Subject, selfSignedError)
-			}
-			if !selfSigned {
-				return fmt.Errorf("root certificate with subject %q is not self-signed. Certificate chain must end with a valid self-signed root certificate", cert.Subject)
-			}
-		} else {
-			// This is to avoid extra/redundant multiple root cert at the end
-			// of certificate-chain
-			selfSigned, selfSignedError := isSelfSigned(cert)
-			// not checking selfSignedError != nil here because we expect
-			// a non-nil err. For a non-root certificate, it shouldn't be
-			// self-signed, hence CheckSignatureFrom would return a non-nil
-			// error.
-			if selfSignedError == nil && selfSigned {
-				if i == 0 {
-					return fmt.Errorf("leaf certificate with subject %q is self-signed. Certificate chain must not contain self-signed leaf certificate", cert.Subject)
-				}
-				return fmt.Errorf("intermediate certificate with subject %q is self-signed. Certificate chain must not contain self-signed intermediate certificate", cert.Subject)
-			}
-			parentCert := certChain[i+1]
-			issuedBy, issuedByError := isIssuedBy(cert, parentCert)
-			if issuedByError != nil {
-				return fmt.Errorf("invalid certificates or certificate with subject %q is not issued by %q. Error: %v", cert.Subject, parentCert.Subject, issuedByError)
-			}
-			if !issuedBy {
-				return fmt.Errorf("certificate with subject %q is not issued by %q", cert.Subject, parentCert.Subject)
-			}
-		}
-
-		if i == 0 {
-			if err := validateLeafCertificate(cert, expectedLeafEku); err != nil {
-				return err
-			}
-		} else {
-			if err := validateCACertificate(cert, i-1); err != nil {
-				return err
-			}
-		}
-	}
-	return nil
-}
-
-func isSelfSigned(cert *x509.Certificate) (bool, error) {
-	return isIssuedBy(cert, cert)
-}
-
-func isIssuedBy(subject *x509.Certificate, issuer *x509.Certificate) (bool, error) {
-	if err := subject.CheckSignatureFrom(issuer); err != nil {
-		return false, err
-	}
-	return bytes.Equal(issuer.RawSubject, subject.RawIssuer), nil
-}
-
-func validateCACertificate(cert *x509.Certificate, expectedPathLen int) error {
-	if err := validateCABasicConstraints(cert, expectedPathLen); err != nil {
-		return err
-	}
-	return validateCAKeyUsage(cert)
-}
-
-func validateLeafCertificate(cert *x509.Certificate, expectedEku x509.ExtKeyUsage) error {
-	if err := validateLeafBasicConstraints(cert); err != nil {
-		return err
-	}
-	if err := validateLeafKeyUsage(cert); err != nil {
-		return err
-	}
-	if err := validateExtendedKeyUsage(cert, expectedEku); err != nil {
-		return err
-	}
-	return validateKeyLength(cert)
-}
-
-func validateCABasicConstraints(cert *x509.Certificate, expectedPathLen int) error {
-	if !cert.BasicConstraintsValid || !cert.IsCA {
-		return fmt.Errorf("certificate with subject %q: ca field in basic constraints must be present, critical, and set to true", cert.Subject)
-	}
-	maxPathLen := cert.MaxPathLen
-	isMaxPathLenPresent := maxPathLen > 0 || (maxPathLen == 0 && cert.MaxPathLenZero)
-	if isMaxPathLenPresent && maxPathLen < expectedPathLen {
-		return fmt.Errorf("certificate with subject %q: expected path length of %d but certificate has path length %d instead", cert.Subject, expectedPathLen, maxPathLen)
-	}
-	return nil
-}
-
-func validateLeafBasicConstraints(cert *x509.Certificate) error {
-	if cert.BasicConstraintsValid && cert.IsCA {
-		return fmt.Errorf("certificate with subject %q: if the basic constraints extension is present, the ca field must be set to false", cert.Subject)
-	}
-	return nil
-}
-
-func validateCAKeyUsage(cert *x509.Certificate) error {
-	if err := validateKeyUsagePresent(cert); err != nil {
-		return err
-	}
-	if cert.KeyUsage&x509.KeyUsageCertSign == 0 {
-		return fmt.Errorf("certificate with subject %q: key usage must have the bit positions for key cert sign set", cert.Subject)
-	}
-	return nil
-}
-
-func validateLeafKeyUsage(cert *x509.Certificate) error {
-	if err := validateKeyUsagePresent(cert); err != nil {
-		return err
-	}
-	if cert.KeyUsage&x509.KeyUsageDigitalSignature == 0 {
-		return fmt.Errorf("The certificate with subject %q is invalid. The key usage must have the bit positions for \"Digital Signature\" set", cert.Subject)
-	}
-
-	var invalidKeyUsages []string
-	if cert.KeyUsage&x509.KeyUsageContentCommitment != 0 {
-		invalidKeyUsages = append(invalidKeyUsages, `"ContentCommitment"`)
-	}
-	if cert.KeyUsage&x509.KeyUsageKeyEncipherment != 0 {
-		invalidKeyUsages = append(invalidKeyUsages, `"KeyEncipherment"`)
-	}
-	if cert.KeyUsage&x509.KeyUsageDataEncipherment != 0 {
-		invalidKeyUsages = append(invalidKeyUsages, `"DataEncipherment"`)
-	}
-	if cert.KeyUsage&x509.KeyUsageKeyAgreement != 0 {
-		invalidKeyUsages = append(invalidKeyUsages, `"KeyAgreement"`)
-	}
-	if cert.KeyUsage&x509.KeyUsageCertSign != 0 {
-		invalidKeyUsages = append(invalidKeyUsages, `"CertSign"`)
-	}
-	if cert.KeyUsage&x509.KeyUsageCRLSign != 0 {
-		invalidKeyUsages = append(invalidKeyUsages, `"CRLSign"`)
-	}
-	if cert.KeyUsage&x509.KeyUsageEncipherOnly != 0 {
-		invalidKeyUsages = append(invalidKeyUsages, `"EncipherOnly"`)
-	}
-	if cert.KeyUsage&x509.KeyUsageDecipherOnly != 0 {
-		invalidKeyUsages = append(invalidKeyUsages, `"DecipherOnly"`)
-	}
-	if len(invalidKeyUsages) > 0 {
-		return fmt.Errorf("The certificate with subject %q is invalid. The key usage must be \"Digital Signature\" only, but found %s", cert.Subject, strings.Join(invalidKeyUsages, ", "))
-	}
-	return nil
-}
-
-func validateKeyUsagePresent(cert *x509.Certificate) error {
-	keyUsageExtensionOid := []int{2, 5, 29, 15}
-
-	var hasKeyUsageExtension bool
-	for _, ext := range cert.Extensions {
-		if ext.Id.Equal(keyUsageExtensionOid) {
-			if !ext.Critical {
-				return fmt.Errorf("certificate with subject %q: key usage extension must be marked critical", cert.Subject)
-			}
-			hasKeyUsageExtension = true
-			break
-		}
-	}
-	if !hasKeyUsageExtension {
-		return fmt.Errorf("certificate with subject %q: key usage extension must be present", cert.Subject)
-	}
-	return nil
-}
-
-func validateExtendedKeyUsage(cert *x509.Certificate, expectedEku x509.ExtKeyUsage) error {
-	if len(cert.ExtKeyUsage) <= 0 {
-		return nil
-	}
-
-	excludedEkus := []x509.ExtKeyUsage{
-		x509.ExtKeyUsageAny,
-		x509.ExtKeyUsageServerAuth,
-		x509.ExtKeyUsageClientAuth,
-		x509.ExtKeyUsageEmailProtection,
-		x509.ExtKeyUsageOCSPSigning,
-	}
-
-	if expectedEku == 0 {
-		excludedEkus = append(excludedEkus, x509.ExtKeyUsageTimeStamping)
-	} else if expectedEku == x509.ExtKeyUsageTimeStamping {
-		excludedEkus = append(excludedEkus, x509.ExtKeyUsageCodeSigning)
-	}
-
-	var hasExpectedEku bool
-	for _, certEku := range cert.ExtKeyUsage {
-		if certEku == expectedEku {
-			hasExpectedEku = true
-			continue
-		}
-		for _, excludedEku := range excludedEkus {
-			if certEku == excludedEku {
-				return fmt.Errorf("certificate with subject %q: extended key usage must not contain %s eku", cert.Subject, ekuToString(excludedEku))
-			}
-		}
-	}
-
-	if expectedEku != 0 && !hasExpectedEku {
-		return fmt.Errorf("certificate with subject %q: extended key usage must contain %s eku", cert.Subject, ekuToString(expectedEku))
-	}
-	return nil
-}
-
-func validateKeyLength(cert *x509.Certificate) error {
-	switch key := cert.PublicKey.(type) {
-	case *rsa.PublicKey:
-		if key.N.BitLen() < 2048 {
-			return fmt.Errorf("certificate with subject %q: rsa public key length must be 2048 bits or higher", cert.Subject)
-		}
-	case *ecdsa.PublicKey:
-		if key.Params().N.BitLen() < 256 {
-			return fmt.Errorf("certificate with subject %q: ecdsa public key length must be 256 bits or higher", cert.Subject)
-		}
-	}
-	return nil
-}
-
-func ekuToString(eku x509.ExtKeyUsage) string {
-	switch eku {
-	case x509.ExtKeyUsageAny:
-		return "Any"
-	case x509.ExtKeyUsageServerAuth:
-		return "ServerAuth"
-	case x509.ExtKeyUsageClientAuth:
-		return "ClientAuth"
-	case x509.ExtKeyUsageOCSPSigning:
-		return "OCSPSigning"
-	case x509.ExtKeyUsageEmailProtection:
-		return "EmailProtection"
-	case x509.ExtKeyUsageCodeSigning:
-		return "CodeSigning"
-	case x509.ExtKeyUsageTimeStamping:
-		return "TimeStamping"
-	default:
-		return fmt.Sprintf("%d", int(eku))
-	}
-}

x509/codesigning_cert_validations.go

@@ -0,0 +1,179 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package x509
+
+import (
+	"bytes"
+	"crypto/x509"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/notaryproject/notation-core-go/internal/oid"
+)
+
+// ValidateCodeSigningCertChain takes an ordered code signing certificate chain
+// and validates issuance from leaf to root
+// Validates certificates according to this spec:
+// https://github.com/notaryproject/notaryproject/blob/main/specs/signature-specification.md#certificate-requirements
+func ValidateCodeSigningCertChain(certChain []*x509.Certificate, signingTime *time.Time) error {
+	if len(certChain) < 1 {
+		return errors.New("certificate chain must contain at least one certificate")
+	}
+
+	// For self-signed signing certificate (not a CA)
+	if len(certChain) == 1 {
+		cert := certChain[0]
+		// check self-signed
+		if err := cert.CheckSignature(cert.SignatureAlgorithm, cert.RawTBSCertificate, cert.Signature); err != nil {
+			return fmt.Errorf("invalid self-signed certificate. subject: %q. Error: %w", cert.Subject, err)
+		}
+		// check self-issued
+		if !bytes.Equal(cert.RawSubject, cert.RawIssuer) {
+			return fmt.Errorf("invalid self-signed certificate. subject: %q. Error: issuer(%s) and subject(%s) are not the same", cert.Subject, cert.Issuer, cert.Subject)
+		}
+		if signedTimeError := validateSigningTime(cert, signingTime); signedTimeError != nil {
+			return signedTimeError
+		}
+		if err := validateCodeSigningLeafCertificate(cert); err != nil {
+			return fmt.Errorf("invalid self-signed certificate. Error: %w", err)
+		}
+		return nil
+	}
+
+	for i, cert := range certChain {
+		if signedTimeError := validateSigningTime(cert, signingTime); signedTimeError != nil {
+			return signedTimeError
+		}
+		if i == len(certChain)-1 {
+			selfSigned, selfSignedError := isSelfSigned(cert)
+			if selfSignedError != nil {
+				return fmt.Errorf("root certificate with subject %q is invalid or not self-signed. Certificate chain must end with a valid self-signed root certificate. Error: %v", cert.Subject, selfSignedError)
+			}
+			if !selfSigned {
+				return fmt.Errorf("root certificate with subject %q is not self-signed. Certificate chain must end with a valid self-signed root certificate", cert.Subject)
+			}
+		} else {
+			// This is to avoid extra/redundant multiple root cert at the end
+			// of certificate-chain
+			selfSigned, selfSignedError := isSelfSigned(cert)
+			// not checking selfSignedError != nil here because we expect
+			// a non-nil err. For a non-root certificate, it shouldn't be
+			// self-signed, hence CheckSignatureFrom would return a non-nil
+			// error.
+			if selfSignedError == nil && selfSigned {
+				if i == 0 {
+					return fmt.Errorf("leaf certificate with subject %q is self-signed. Certificate chain must not contain self-signed leaf certificate", cert.Subject)
+				}
+				return fmt.Errorf("intermediate certificate with subject %q is self-signed. Certificate chain must not contain self-signed intermediate certificate", cert.Subject)
+			}
+			parentCert := certChain[i+1]
+			issuedBy, issuedByError := isIssuedBy(cert, parentCert)
+			if issuedByError != nil {
+				return fmt.Errorf("invalid certificates or certificate with subject %q is not issued by %q. Error: %v", cert.Subject, parentCert.Subject, issuedByError)
+			}
+			if !issuedBy {
+				return fmt.Errorf("certificate with subject %q is not issued by %q", cert.Subject, parentCert.Subject)
+			}
+		}
+
+		if i == 0 {
+			if err := validateCodeSigningLeafCertificate(cert); err != nil {
+				return err
+			}
+		} else {
+			if err := validateCodeSigningCACertificate(cert, i-1); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+func validateCodeSigningCACertificate(cert *x509.Certificate, expectedPathLen int) error {
+	if err := validateCABasicConstraints(cert, expectedPathLen); err != nil {
+		return err
+	}
+	return validateCodeSigningCAKeyUsage(cert)
+}
+
+func validateCodeSigningLeafCertificate(cert *x509.Certificate) error {
+	if err := validateLeafBasicConstraints(cert); err != nil {
+		return err
+	}
+	if err := validateCodeSigningLeafKeyUsage(cert); err != nil {
+		return err
+	}
+	if err := validateCodeSigningExtendedKeyUsage(cert); err != nil {
+		return err
+	}
+	return validateSignatureAlgorithm(cert)
+}
+
+func validateCodeSigningCAKeyUsage(cert *x509.Certificate) error {
+	if err := validateCodeSigningKeyUsagePresent(cert); err != nil {
+		return err
+	}
+	if cert.KeyUsage&x509.KeyUsageCertSign == 0 {
+		return fmt.Errorf("certificate with subject %q: key usage must have the bit positions for key cert sign set", cert.Subject)
+	}
+	return nil
+}
+
+func validateCodeSigningLeafKeyUsage(cert *x509.Certificate) error {
+	if err := validateCodeSigningKeyUsagePresent(cert); err != nil {
+		return err
+	}
+	return validateLeafKeyUsage(cert)
+}
+
+func validateCodeSigningKeyUsagePresent(cert *x509.Certificate) error {
+	var hasKeyUsageExtension bool
+	for _, ext := range cert.Extensions {
+		if ext.Id.Equal(oid.KeyUsage) {
+			if !ext.Critical {
+				return fmt.Errorf("certificate with subject %q: key usage extension must be marked critical", cert.Subject)
+			}
+			hasKeyUsageExtension = true
+			break
+		}
+	}
+	if !hasKeyUsageExtension {
+		return fmt.Errorf("certificate with subject %q: key usage extension must be present", cert.Subject)
+	}
+	return nil
+}
+
+func validateCodeSigningExtendedKeyUsage(cert *x509.Certificate) error {
+	if len(cert.ExtKeyUsage) == 0 {
+		return nil
+	}
+
+	excludedEkus := []x509.ExtKeyUsage{
+		x509.ExtKeyUsageServerAuth,
+		x509.ExtKeyUsageClientAuth,
+		x509.ExtKeyUsageEmailProtection,
+		x509.ExtKeyUsageTimeStamping,
+		x509.ExtKeyUsageOCSPSigning,
+	}
+
+	for _, certEku := range cert.ExtKeyUsage {
+		for _, excludedEku := range excludedEkus {
+			if certEku == excludedEku {
+				return fmt.Errorf("certificate with subject %q: extended key usage must not contain %s eku", cert.Subject, ekuToString(excludedEku))
+			}
+		}
+	}
+	return nil
+}

x509/codesigning_cert_validations_test.go

@@ -17,10 +17,13 @@ import (
 	"crypto/x509"
 	"crypto/x509/pkix"
 	_ "embed"
-	"encoding/asn1"
+	"errors"
+	"os"
+	"strings"
 	"testing"
 	"time"
 
+	"github.com/notaryproject/notation-core-go/internal/oid"
 	"github.com/notaryproject/notation-core-go/testhelper"
 )
 
@@ -100,25 +103,6 @@ var codeSigningLeafPem = "-----BEGIN CERTIFICATE-----\n" +
 	"cwtsQn/iENuvFcfRHcFhvRjEFrIP+Ugx\n" +
 	"-----END CERTIFICATE-----"
 
-var timeStampingLeafPem = "-----BEGIN CERTIFICATE-----\n" +
-	"MIIC5TCCAc2gAwIBAgIBATANBgkqhkiG9w0BAQsFADAYMRYwFAYDVQQDDA1JbnRl\n" +
-	"cm1lZGlhdGUyMCAXDTIyMDYzMDE5MjAwNFoYDzMwMjExMDMxMTkyMDA0WjAbMRkw\n" +
-	"FwYDVQQDDBBUaW1lU3RhbXBpbmdMZWFmMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8A\n" +
-	"MIIBCgKCAQEAyx2ispY5C5sQCiLAuCUTp4wv+fpgHwzE4an8eqi+Jrm0tEabTdzP\n" +
-	"IdZFRYPZbgRx+D9DKeN76f+rt51G9gOX77fYWyIXgnVL4UAYNlQj58hqZ0IO22vT\n" +
-	"nIFiDbJoSPuamQaLZNuluiirUwJv1uqSQiEnWHC4LhKwNOo4UHH5S3XkkYRpdFBF\n" +
-	"Tm4uOTaQJA9dfCh+0wbe7ZlEjDiuk1GTSQu69EPIl4IK7aEWqdvk2z1Pg4YkgJZX\n" +
-	"mWzkECNayUiBeHj7lL5ZnyZeki2l77WzXe/j5dgQ9E2+63hfBew+O/XeS/Tm/TyQ\n" +
-	"0P8bQre6vbn9820Cpyg82fd1+5bwYedwVwIDAQABozUwMzAOBgNVHQ8BAf8EBAMC\n" +
-	"B4AwDAYDVR0TAQH/BAIwADATBgNVHSUEDDAKBggrBgEFBQcDCDANBgkqhkiG9w0B\n" +
-	"AQsFAAOCAQEAB9Z80K17p4J3VCqVcKyhgkzzYPoKiBWFThVwxS2+TKY0x4zezSAT\n" +
-	"69Nmf7NkVH4XyvCEUfgdWYst4t41rH3b5MTMOc5/nPeMccDWT0eZRivodF5hFWZd\n" +
-	"2QSFiMHmfUhnglY0ocLbfKeI/QoSGiPyBWO0SK6qOszRi14lP0TpgvgNDtMY/Jj5\n" +
-	"AyINT6o0tyYJvYE23/7ysT3U6pq50M4vOZiSuRys83As/qvlDIDKe8OVlDt6xRvr\n" +
-	"fqdMFWSk6Iay2OCfYcjUbTutMzSI7dvhDivn5FKnNA6M7QD1lqb7V9fymgrQTsth\n" +
-	"We9tUxypXgMjYN74QEHYxEAIfNOTeBppWw==\n" +
-	"-----END CERTIFICATE-----"
-
 var unrelatedCertPem = "-----BEGIN CERTIFICATE-----\n" +
 	"MIIC6jCCAdKgAwIBAgIJAJOlT2AUbsZiMA0GCSqGSIb3DQEBCwUAMBAxDjAMBgNV\n" +
 	"BAMMBUhlbGxvMCAXDTIyMDYyNTAzMTcyM1oYDzIxMjIwNjAxMDMxNzIzWjAQMQ4w\n" +
@@ -183,7 +167,6 @@ var rootCert = parseCertificateFromString(rootCertPem)
 var intermediateCert1 = parseCertificateFromString(intermediateCertPem1)
 var intermediateCert2 = parseCertificateFromString(intermediateCertPem2)
 var codeSigningCert = parseCertificateFromString(codeSigningLeafPem)
-var timeStampingCert = parseCertificateFromString(timeStampingLeafPem)
 var unrelatedCert = parseCertificateFromString(unrelatedCertPem)
 var intermediateCertInvalidPathLen = parseCertificateFromString(intermediateCertInvalidPathLenPem)
 var codeSigningLeafInvalidPathLen = parseCertificateFromString(codeSigningLeafInvalidPathLenPem)
@@ -211,15 +194,6 @@ func TestValidCodeSigningChain(t *testing.T) {
 	}
 }
 
-func TestValidTimeStampingChain(t *testing.T) {
-	certChain := []*x509.Certificate{timeStampingCert, intermediateCert2, intermediateCert1, rootCert}
-	signingTime := time.Now()
-
-	if err := ValidateTimeStampingCertChain(certChain, &signingTime); err != nil {
-		t.Fatal(err)
-	}
-}
-
 func TestFailEmptyChain(t *testing.T) {
 	signingTime := time.Now()
 	err := ValidateCodeSigningCertChain(nil, &signingTime)
@@ -227,12 +201,71 @@ func TestFailEmptyChain(t *testing.T) {
 	assertErrorEqual("certificate chain must contain at least one certificate", err, t)
 }
 
+func TestFailNonSelfSignedLeafCert(t *testing.T) {
+	signingTime := time.Now()
+	err := ValidateCodeSigningCertChain([]*x509.Certificate{codeSigningCert}, &signingTime)
+
+	assertErrorEqual("invalid self-signed certificate. subject: \"CN=CodeSigningLeaf\". Error: crypto/rsa: verification error", err, t)
+}
+
+func TestFailSelfIssuedCodeSigningCert(t *testing.T) {
+	chainTuple := testhelper.GetRevokableRSATimestampChain(2)
+	// the leaf certiifcate and the root certificate share the same private key
+	// so the leaf is also self-signed but issuer and subject are different
+	chain := []*x509.Certificate{chainTuple[0].Cert}
+	signingTime := time.Now()
+	err := ValidateCodeSigningCertChain(chain, &signingTime)
+	assertErrorEqual("invalid self-signed certificate. subject: \"CN=Notation Test Revokable RSA Chain Cert 2,O=Notary,L=Seattle,ST=WA,C=US\". Error: issuer(CN=Notation Test Revokable RSA Chain Cert Root,O=Notary,L=Seattle,ST=WA,C=US) and subject(CN=Notation Test Revokable RSA Chain Cert 2,O=Notary,L=Seattle,ST=WA,C=US) are not the same", err, t)
+}
+
+func TestInvalidCodeSigningCertSigningTime(t *testing.T) {
+	chainTuple := testhelper.GetRevokableRSATimestampChain(2)
+	chain := []*x509.Certificate{chainTuple[1].Cert}
+	signingTime := time.Date(2021, 7, 7, 20, 48, 42, 0, time.UTC)
+
+	expectPrefix := "certificate with subject \"CN=Notation Test Revokable RSA Chain Cert Root,O=Notary,L=Seattle,ST=WA,C=US\" was invalid at signing time of 2021-07-07 20:48:42 +0000 UTC"
+	err := ValidateCodeSigningCertChain(chain, &signingTime)
+	if !strings.HasPrefix(err.Error(), expectPrefix) {
+		t.Errorf("expected error to start with %q, got %q", expectPrefix, err)
+	}
+}
+
 func TestFailInvalidSigningTime(t *testing.T) {
 	certChain := []*x509.Certificate{codeSigningCert, intermediateCert2, intermediateCert1, rootCert}
 
 	st := time.Unix(1625690922, 0)
 	err := ValidateCodeSigningCertChain(certChain, &st)
-	assertErrorEqual("certificate with subject \"CN=CodeSigningLeaf\" was not valid at signing time of 2021-07-07 20:48:42 +0000 UTC", err, t)
+	assertErrorEqual("certificate with subject \"CN=CodeSigningLeaf\" was invalid at signing time of 2021-07-07 20:48:42 +0000 UTC. Certificate is valid from [2022-06-30 19:20:03 +0000 UTC] to [3021-10-31 19:20:03 +0000 UTC]", err, t)
+}
+
+func TestValidateSigningTime(t *testing.T) {
+	// codeSigningCert is valid from 2022-06-30 19:20:03 +0000 UTC to 3021-10-31 19:20:03 +0000 UTC
+	testCases := []struct {
+		name        string
+		certChain   *x509.Certificate
+		signingTime time.Time
+		expectErr   string
+	}{
+		{"invalid before certificate period",
+			codeSigningCert,
+			time.Date(2022, 6, 29, 0, 0, 0, 0, time.UTC),
+			"certificate with subject \"CN=CodeSigningLeaf\" was invalid at signing time of 2022-06-29 00:00:00 +0000 UTC. Certificate is valid from [2022-06-30 19:20:03 +0000 UTC] to [3021-10-31 19:20:03 +0000 UTC]"},
+		{"invalid after certificate period",
+			codeSigningCert,
+			time.Date(3021, 11, 1, 0, 0, 0, 0, time.UTC),
+			"certificate with subject \"CN=CodeSigningLeaf\" was invalid at signing time of 3021-11-01 00:00:00 +0000 UTC. Certificate is valid from [2022-06-30 19:20:03 +0000 UTC] to [3021-10-31 19:20:03 +0000 UTC]"},
+		{"valid in certificate period",
+			codeSigningCert,
+			time.Date(2023, 10, 10, 0, 0, 0, 0, time.UTC),
+			""},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			if err := validateSigningTime(tc.certChain, &tc.signingTime); err != nil {
+				assertErrorEqual(tc.expectErr, err, t)
+			}
+		})
+	}
 }
 
 func TestFailChainNotEndingInRoot(t *testing.T) {
@@ -310,13 +343,13 @@ func TestInvalidSelfSignedSigningCertificate(t *testing.T) {
 // ---------------- CA Validations ----------------
 
 func TestValidCa(t *testing.T) {
-	if err := validateCACertificate(rootCert, 2); err != nil {
+	if err := validateCodeSigningCACertificate(rootCert, 2); err != nil {
 		t.Fatal(err)
 	}
 }
 
 func TestFailInvalidPathLenCa(t *testing.T) {
-	err := validateCACertificate(rootCert, 3)
+	err := validateCodeSigningCACertificate(rootCert, 3)
 	assertErrorEqual("certificate with subject \"CN=Root\": expected path length of 3 but certificate has path length 2 instead", err, t)
 }
 
@@ -340,7 +373,7 @@ var noBasicConstraintsCaPem = "-----BEGIN CERTIFICATE-----\n" +
 var noBasicConstraintsCa = parseCertificateFromString(noBasicConstraintsCaPem)
 
 func TestFailNoBasicConstraintsCa(t *testing.T) {
-	err := validateCACertificate(noBasicConstraintsCa, 3)
+	err := validateCodeSigningCACertificate(noBasicConstraintsCa, 3)
 	assertErrorEqual("certificate with subject \"CN=Hello\": ca field in basic constraints must be present, critical, and set to true", err, t)
 }
 
@@ -364,7 +397,7 @@ var basicConstraintsNotCaPem = "-----BEGIN CERTIFICATE-----\n" +
 var basicConstraintsNotCa = parseCertificateFromString(basicConstraintsNotCaPem)
 
 func TestFailBasicConstraintsNotCa(t *testing.T) {
-	err := validateCACertificate(basicConstraintsNotCa, 3)
+	err := validateCodeSigningCACertificate(basicConstraintsNotCa, 3)
 	assertErrorEqual("certificate with subject \"CN=Hello\": ca field in basic constraints must be present, critical, and set to true", err, t)
 }
 
@@ -388,7 +421,7 @@ var kuNotCriticalCertSignCaPem = "-----BEGIN CERTIFICATE-----\n" +
 var kuNotCriticalCertSignCa = parseCertificateFromString(kuNotCriticalCertSignCaPem)
 
 func TestFailKuNotCriticalCertSignCa(t *testing.T) {
-	err := validateCACertificate(kuNotCriticalCertSignCa, 3)
+	err := validateCodeSigningCACertificate(kuNotCriticalCertSignCa, 3)
 	assertErrorEqual("certificate with subject \"CN=Hello\": key usage extension must be marked critical", err, t)
 }
 
@@ -412,7 +445,7 @@ var kuMissingCaPem = "-----BEGIN CERTIFICATE-----\n" +
 var kuMissingCa = parseCertificateFromString(kuMissingCaPem)
 
 func TestFailKuMissingCa(t *testing.T) {
-	err := validateCACertificate(kuMissingCa, 3)
+	err := validateCodeSigningCACertificate(kuMissingCa, 3)
 	assertErrorEqual("certificate with subject \"CN=Hello\": key usage extension must be present", err, t)
 }
 
@@ -436,11 +469,11 @@ var kuNotCertSignCaPem = "-----BEGIN CERTIFICATE-----\n" +
 var kuNotCertSignCa = parseCertificateFromString(kuNotCertSignCaPem)
 
 func TestFailKuNotCertSignCa(t *testing.T) {
-	err := validateCACertificate(kuNotCertSignCa, 3)
+	err := validateCodeSigningCACertificate(kuNotCertSignCa, 3)
 	assertErrorEqual("certificate with subject \"CN=Hello\": key usage must have the bit positions for key cert sign set", err, t)
 }
 
-// ---------------- Code-Signing + Time-Stamping Leaf Validations ----------------
+// ---------------- Code-Signing Validations ----------------
 
 var validNoOptionsLeafPem = "-----BEGIN CERTIFICATE-----\n" +
 	"MIICtzCCAZ+gAwIBAgIJAL+FUPhO8J8cMA0GCSqGSIb3DQEBCwUAMBAxDjAMBgNV\n" +
@@ -462,7 +495,7 @@ var validNoOptionsLeafPem = "-----BEGIN CERTIFICATE-----\n" +
 var validNoOptionsLeaf = parseCertificateFromString(validNoOptionsLeafPem)
 
 func TestValidNoOptionsLeaf(t *testing.T) {
-	if err := validateLeafCertificate(validNoOptionsLeaf, x509.ExtKeyUsageCodeSigning); err != nil {
+	if err := validateCodeSigningLeafCertificate(validNoOptionsLeaf); err != nil {
 		t.Fatal(err)
 	}
 }
@@ -487,7 +520,7 @@ var caTrueLeafPem = "-----BEGIN CERTIFICATE-----\n" +
 var caTrueLeaf = parseCertificateFromString(caTrueLeafPem)
 
 func TestFailCaTrueLeaf(t *testing.T) {
-	err := validateLeafCertificate(caTrueLeaf, x509.ExtKeyUsageCodeSigning)
+	err := validateCodeSigningLeafCertificate(caTrueLeaf)
 	assertErrorEqual("certificate with subject \"CN=Hello\": if the basic constraints extension is present, the ca field must be set to false", err, t)
 }
 
@@ -511,8 +544,8 @@ var kuNoDigitalSignatureLeafPem = "-----BEGIN CERTIFICATE-----\n" +
 var kuNoDigitalSignatureLeaf = parseCertificateFromString(kuNoDigitalSignatureLeafPem)
 
 func TestFailKuNoDigitalSignatureLeaf(t *testing.T) {
-	err := validateLeafCertificate(kuNoDigitalSignatureLeaf, x509.ExtKeyUsageCodeSigning)
+	err := validateCodeSigningLeafCertificate(kuNoDigitalSignatureLeaf)
-	assertErrorEqual("The certificate with subject \"CN=Hello\" is invalid. The key usage must have the bit positions for \"Digital Signature\" set", err, t)
+	assertErrorEqual("the certificate with subject \"CN=Hello\" is invalid. The key usage must have the bit positions for \"Digital Signature\" set", err, t)
 }
 
 var kuWrongValuesLeafPem = "-----BEGIN CERTIFICATE-----\n" +
@@ -535,8 +568,8 @@ var kuWrongValuesLeafPem = "-----BEGIN CERTIFICATE-----\n" +
 var kuWrongValuesLeaf = parseCertificateFromString(kuWrongValuesLeafPem)
 
 func TestFailKuWrongValuesLeaf(t *testing.T) {
-	err := validateLeafCertificate(kuWrongValuesLeaf, x509.ExtKeyUsageCodeSigning)
+	err := validateCodeSigningLeafCertificate(kuWrongValuesLeaf)
-	assertErrorEqual("The certificate with subject \"CN=Hello\" is invalid. The key usage must be \"Digital Signature\" only, but found \"CertSign\", \"CRLSign\"", err, t)
+	assertErrorEqual("the certificate with subject \"CN=Hello\" is invalid. The key usage must be \"Digital Signature\" only, but found \"CertSign\", \"CRLSign\"", err, t)
 }
 
 var rsaKeyTooSmallLeafPem = "-----BEGIN CERTIFICATE-----\n" +
@@ -554,8 +587,8 @@ var rsaKeyTooSmallLeafPem = "-----BEGIN CERTIFICATE-----\n" +
 var rsaKeyTooSmallLeaf = parseCertificateFromString(rsaKeyTooSmallLeafPem)
 
 func TestFailRsaKeyTooSmallLeaf(t *testing.T) {
-	err := validateLeafCertificate(rsaKeyTooSmallLeaf, x509.ExtKeyUsageCodeSigning)
+	err := validateCodeSigningLeafCertificate(rsaKeyTooSmallLeaf)
-	assertErrorEqual("certificate with subject \"CN=Hello\": rsa public key length must be 2048 bits or higher", err, t)
+	assertErrorEqual("certificate with subject \"CN=Hello\": rsa key size 1024 bits is not supported", err, t)
 }
 
 var ecdsaKeyTooSmallLeafPem = "-----BEGIN CERTIFICATE-----\n" +
@@ -570,141 +603,21 @@ var ecdsaKeyTooSmallLeafPem = "-----BEGIN CERTIFICATE-----\n" +
 var ecdsaKeyTooSmallLeaf = parseCertificateFromString(ecdsaKeyTooSmallLeafPem)
 
 func TestFailEcdsaKeyTooSmallLeaf(t *testing.T) {
-	err := validateLeafCertificate(ecdsaKeyTooSmallLeaf, x509.ExtKeyUsageCodeSigning)
+	err := validateCodeSigningLeafCertificate(ecdsaKeyTooSmallLeaf)
-	assertErrorEqual("certificate with subject \"CN=Hello\": ecdsa public key length must be 256 bits or higher", err, t)
+	assertErrorEqual("certificate with subject \"CN=Hello\": ecdsa key size 224 bits is not supported", err, t)
 }
 
 // ---------------- Code-Signing Leaf Validations ----------------
 
 func TestValidFullOptionsCodeLeaf(t *testing.T) {
-	if err := validateLeafCertificate(codeSigningCert, x509.ExtKeyUsageCodeSigning); err != nil {
+	if err := validateCodeSigningLeafCertificate(codeSigningCert); err != nil {
 		t.Fatal(err)
 	}
 }
 
-var ekuWrongValuesCodeLeafPem = "-----BEGIN CERTIFICATE-----\n" +
-	"MIIC6jCCAdKgAwIBAgIJAKZJHdWFNYPlMA0GCSqGSIb3DQEBCwUAMBAxDjAMBgNV\n" +
-	"BAMMBUhlbGxvMCAXDTIyMDYyNTAzMDEwM1oYDzIxMjIwNjAxMDMwMTAzWjAQMQ4w\n" +
-	"DAYDVQQDDAVIZWxsbzCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAK2t\n" +
-	"EFpNOJkX7B78d9ahTl5MXGWyKIjgfg1PhkYwHKHJWBiqHa1OUewfUG4ouVuaAvJ+\n" +
-	"GPzcxt23/J3jK+3/szrzpBNv1f0vgIa+mqaRQDW2m/wfWw3kpcwxlRcL7GnCeHbv\n" +
-	"gRFDXQW6MhKgGgKdQ5ezV+p01eF+CzMhUe+bZO+mvgxj36MJHzLMFHyh3x4/+z4x\n" +
-	"qRKmj4uUqJ2FJLlQEk92vPE/N3r7rEWa6gd4mBZ+DsZSrCbVPXchS2mCkeg70qxA\n" +
-	"4840qVLZ5eFxtqnTEUNytu3ug/8ydV9VmuT+C5fQYUp3Fl7D1QxHxWYTVTKdenCY\n" +
-	"jxcJHW1cUWZQlgPTLq8CAwEAAaNFMEMwDgYDVR0PAQH/BAQDAgeAMDEGA1UdJQQq\n" +
-	"MCgGCCsGAQUFBwMDBggrBgEFBQcDAQYIKwYBBQUHAwQGCCsGAQUFBwMIMA0GCSqG\n" +
-	"SIb3DQEBCwUAA4IBAQBRfpNRu79i47yp73LWTKrnZRiLC4JAI3I3w5TTx8m2tYkq\n" +
-	"tkSCP3Sn4y6VjKqo9Xtlt/bBLypw7XAOZOUZLEaoCjwRmAwq74VHAxDZO1LfFlKd\n" +
-	"au8G3xhKjc5prOMJ2g4DELOcyDoLDlwYqQ/jfG/t8b0P37yakFVffSzIA7D0BjmS\n" +
-	"OnWrGOJO/IJZjiaTdQkg+n5jk4FNqhwW91em64/M3MOmib3plnl89MgR90kuvQOV\n" +
-	"ctDBylt8M61MgnbzeunAq4aKYJc4IeeIH++g4F3/pqyoC95sAZP+A6+LkmBDOcyE\n" +
-	"5wUmNtUsL9xxKIUCvPR1JtiLNxHrfendWiuJnW1M\n" +
-	"-----END CERTIFICATE-----"
-var ekuWrongValuesCodeLeaf = parseCertificateFromString(ekuWrongValuesCodeLeafPem)
-
-func TestFailEkuWrongValuesCodeLeaf(t *testing.T) {
-	err := validateLeafCertificate(ekuWrongValuesCodeLeaf, x509.ExtKeyUsageCodeSigning)
-	assertErrorEqual("certificate with subject \"CN=Hello\": extended key usage must not contain ServerAuth eku", err, t)
-}
-
-var ekuMissingCodeSigningLeafPem = "-----BEGIN CERTIFICATE-----\n" +
-	"MIICzDCCAbSgAwIBAgIJAJtYOfTu82KRMA0GCSqGSIb3DQEBCwUAMBAxDjAMBgNV\n" +
-	"BAMMBUhlbGxvMCAXDTIyMDYyNTAzMTMxM1oYDzIxMjIwNjAxMDMxMzEzWjAQMQ4w\n" +
-	"DAYDVQQDDAVIZWxsbzCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBALQN\n" +
-	"GJKHE6cdcmrHkxXOTawWgYEF1X42IOK7gAXFg+KBPHPw4npDjUclLX0sY3XjBuhT\n" +
-	"wI5DRATSNTV2ba3+DpFuH3D+Hbfjil91AG8XzormUPOOCbZqJxSKYAIZfPQGdUvV\n" +
-	"UBulnbDsije00HoNZ03IvdjxbB/9y6a3qQEvIUaEjaZBH3s/YYQIiEmKu6eDpj3R\n" +
-	"PnUcrP5b7jBMA/Vb8joLM0InzqGPRLPFAPf5womAjxZSsrgyVeA1xSm+6KtXMmaA\n" +
-	"IKYwNVAOnhfqgUk0tlaRyXXji2T1M9w9l5XUA1iNOMcjTUTfFa5KW7c0TLTcK6vW\n" +
-	"Eq1BEXUEw7HP7DQUjycCAwEAAaMnMCUwDgYDVR0PAQH/BAQDAgeAMBMGA1UdJQQM\n" +
-	"MAoGCCsGAQUFBwMJMA0GCSqGSIb3DQEBCwUAA4IBAQCSr6A/YAMd6lisgipR0UCA\n" +
-	"4Ye/1kl0jglT7stLTfftSeXgCKXYlwus9VSpZBtg+RvJkihlLNT6vtsiTMfJUBBc\n" +
-	"jALLKYUQuCw9sReAbfvecIfc2bUve6X8isLWDVnxlC1udx2WG3lIfW2Sgs/dYeZW\n" +
-	"yqLTagK5GLlDfg9gBpHLmQYOmshhI85ObOioUAiWTW+S6mx4Bphgl7dlcUabJxEJ\n" +
-	"MpJJiGPkUUUCuYkp31E7S4JRbSXSkaHefZxB5fvhlbnACeqnOtMG/IKaTjCUemkK\n" +
-	"ZRmJ0Al1PTWs+Dn8zLzexP/LkmQZU/FUMxeat/dAnc2blDbVnAsvcvnutXGHoZH5\n" +
-	"-----END CERTIFICATE-----"
-var ekuMissingCodeSigningLeaf = parseCertificateFromString(ekuMissingCodeSigningLeafPem)
-
-func TestFailEkuMissingCodeSigningLeaf(t *testing.T) {
-	err := validateLeafCertificate(ekuMissingCodeSigningLeaf, x509.ExtKeyUsageCodeSigning)
-	assertErrorEqual("certificate with subject \"CN=Hello\": extended key usage must not contain OCSPSigning eku", err, t)
-}
-
-// ---------------- Time-Stamping Leaf Validations ----------------
-
-func TestValidFullOptionsTimeLeaf(t *testing.T) {
-	if err := validateLeafCertificate(timeStampingCert, x509.ExtKeyUsageTimeStamping); err != nil {
-		t.Fatal(err)
-	}
-}
-
-var ekuWrongValuesTimeLeafPem = "-----BEGIN CERTIFICATE-----\n" +
-	"MIIC6jCCAdKgAwIBAgIJAJOlT2AUbsZiMA0GCSqGSIb3DQEBCwUAMBAxDjAMBgNV\n" +
-	"BAMMBUhlbGxvMCAXDTIyMDYyNTAzMTcyM1oYDzIxMjIwNjAxMDMxNzIzWjAQMQ4w\n" +
-	"DAYDVQQDDAVIZWxsbzCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAOZe\n" +
-	"9zjKWNlFD/HGrkaAI9mh9Fw1gF8S2tphQD/aPd9IS4HJJEQRkKz5oeHj2g1Y6TEk\n" +
-	"plODrKlnoLe+ZFNFFD4xMVV55aQSJDTljCLPwIZt2VewlaAhIImYihOJvJFST1zW\n" +
-	"K2NW4eLxt0awbE/YzL6beH4A6UsrcXcnN0KKiu6YD1/d5TezJoTQBMo6fboltuce\n" +
-	"P/+RMxyqpvip7nyFF3Yrmhumb7DKJrmSfSjdziI5QoUqzqVgqJ8pXMRb3ZOKb499\n" +
-	"d9RRxGkox93iOdSSlaP3FEl8VK9KqnD+MNhjVZbeYTfjm9UVdp91VLP1E/yfMXz+\n" +
-	"fZhYkublK6v3GWSEcb0CAwEAAaNFMEMwDgYDVR0PAQH/BAQDAgeAMDEGA1UdJQQq\n" +
-	"MCgGCCsGAQUFBwMIBggrBgEFBQcDAQYIKwYBBQUHAwQGCCsGAQUFBwMIMA0GCSqG\n" +
-	"SIb3DQEBCwUAA4IBAQCaQZ+ws93F1azT6SKBYvBRBCj07+2DtNI83Q53GxrVy2vU\n" +
-	"rP1ULX7beY87amy6kQcqnQ0QSaoLK+CDL88pPxR2PBzCauz70rMRY8O/KrrLcfwd\n" +
-	"D5HM9DcbneqXQyfh0ZQpt0wK5wux0MFh2sAEv76jgYBMHq2zc+19skAW/oBtTUty\n" +
-	"i/IdOVeO589KXwJzEJmKiswN9zKo9KGgAlKS05zohjv40AOCAs+8Q2lOJjRMq4Ji\n" +
-	"z21qor5e/5+NnGY+2p4A7PbN+QnDdRC3y16dESRN50o5x6CwUWQO74+uRjrAWYCm\n" +
-	"f/Y7qdOf5zZbY21n8KnLcFOsKhwv4t40Y/LQqN/L\n" +
-	"-----END CERTIFICATE-----"
-var ekuWrongValuesTimeLeaf = parseCertificateFromString(ekuWrongValuesTimeLeafPem)
-
-func TestFailEkuWrongValuesTimeLeaf(t *testing.T) {
-	err := validateLeafCertificate(ekuWrongValuesTimeLeaf, x509.ExtKeyUsageTimeStamping)
-	assertErrorEqual("certificate with subject \"CN=Hello\": extended key usage must not contain ServerAuth eku", err, t)
-}
-
-var ekuMissingTimeStampingLeafPem = "-----BEGIN CERTIFICATE-----\n" +
-	"MIICzDCCAbSgAwIBAgIJAJtYOfTu82KRMA0GCSqGSIb3DQEBCwUAMBAxDjAMBgNV\n" +
-	"BAMMBUhlbGxvMCAXDTIyMDYyNTAzMTMxM1oYDzIxMjIwNjAxMDMxMzEzWjAQMQ4w\n" +
-	"DAYDVQQDDAVIZWxsbzCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBALQN\n" +
-	"GJKHE6cdcmrHkxXOTawWgYEF1X42IOK7gAXFg+KBPHPw4npDjUclLX0sY3XjBuhT\n" +
-	"wI5DRATSNTV2ba3+DpFuH3D+Hbfjil91AG8XzormUPOOCbZqJxSKYAIZfPQGdUvV\n" +
-	"UBulnbDsije00HoNZ03IvdjxbB/9y6a3qQEvIUaEjaZBH3s/YYQIiEmKu6eDpj3R\n" +
-	"PnUcrP5b7jBMA/Vb8joLM0InzqGPRLPFAPf5womAjxZSsrgyVeA1xSm+6KtXMmaA\n" +
-	"IKYwNVAOnhfqgUk0tlaRyXXji2T1M9w9l5XUA1iNOMcjTUTfFa5KW7c0TLTcK6vW\n" +
-	"Eq1BEXUEw7HP7DQUjycCAwEAAaMnMCUwDgYDVR0PAQH/BAQDAgeAMBMGA1UdJQQM\n" +
-	"MAoGCCsGAQUFBwMJMA0GCSqGSIb3DQEBCwUAA4IBAQCSr6A/YAMd6lisgipR0UCA\n" +
-	"4Ye/1kl0jglT7stLTfftSeXgCKXYlwus9VSpZBtg+RvJkihlLNT6vtsiTMfJUBBc\n" +
-	"jALLKYUQuCw9sReAbfvecIfc2bUve6X8isLWDVnxlC1udx2WG3lIfW2Sgs/dYeZW\n" +
-	"yqLTagK5GLlDfg9gBpHLmQYOmshhI85ObOioUAiWTW+S6mx4Bphgl7dlcUabJxEJ\n" +
-	"MpJJiGPkUUUCuYkp31E7S4JRbSXSkaHefZxB5fvhlbnACeqnOtMG/IKaTjCUemkK\n" +
-	"ZRmJ0Al1PTWs+Dn8zLzexP/LkmQZU/FUMxeat/dAnc2blDbVnAsvcvnutXGHoZH5\n" +
-	"-----END CERTIFICATE-----"
-var ekuMissingTimeStampingLeaf = parseCertificateFromString(ekuMissingTimeStampingLeafPem)
-
-func TestFailEkuMissingTimeStampingLeaf(t *testing.T) {
-	err := validateLeafCertificate(ekuMissingTimeStampingLeaf, x509.ExtKeyUsageTimeStamping)
-	assertErrorEqual("certificate with subject \"CN=Hello\": extended key usage must not contain OCSPSigning eku", err, t)
-}
-
-// ---------------- Utility Methods ----------------
-
-func parseCertificateFromString(certPem string) *x509.Certificate {
-	stringAsBytes := []byte(certPem)
-	cert, _ := parseCertificates(stringAsBytes)
-	return cert[0]
-}
-
-func assertErrorEqual(expected string, err error, t *testing.T) {
-	if err == nil || expected != err.Error() {
-		t.Fatalf("Expected error \"%v\" but was \"%v\"", expected, err)
-	}
-}
-
 func TestValidateLeafKeyUsage(t *testing.T) {
 	extensions := []pkix.Extension{{
-		Id:       asn1.ObjectIdentifier{2, 5, 29, 15}, // OID for KeyUsage
+		Id:       oid.KeyUsage,
 		Critical: true,
 	}}
 
@@ -729,7 +642,7 @@ func TestValidateLeafKeyUsage(t *testing.T) {
 				KeyUsage:   x509.KeyUsageDigitalSignature | x509.KeyUsageContentCommitment,
 				Extensions: extensions,
 			},
-			expectedErrMsg: "The certificate with subject \"CN=Test CN\" is invalid. The key usage must be \"Digital Signature\" only, but found \"ContentCommitment\"",
+			expectedErrMsg: "",
 		},
 		{
 			name: "Missing DigitalSignature usage",
@@ -738,7 +651,7 @@ func TestValidateLeafKeyUsage(t *testing.T) {
 				KeyUsage:   x509.KeyUsageCertSign,
 				Extensions: extensions,
 			},
-			expectedErrMsg: "The certificate with subject \"CN=Test CN\" is invalid. The key usage must have the bit positions for \"Digital Signature\" set",
+			expectedErrMsg: "the certificate with subject \"CN=Test CN\" is invalid. The key usage must have the bit positions for \"Digital Signature\" set",
 		},
 		{
 			name: "Invalid KeyEncipherment usage",
@@ -747,7 +660,7 @@ func TestValidateLeafKeyUsage(t *testing.T) {
 				KeyUsage:   x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment,
 				Extensions: extensions,
 			},
-			expectedErrMsg: "The certificate with subject \"CN=Test CN\" is invalid. The key usage must be \"Digital Signature\" only, but found \"KeyEncipherment\"",
+			expectedErrMsg: "the certificate with subject \"CN=Test CN\" is invalid. The key usage must be \"Digital Signature\" only, but found \"KeyEncipherment\"",
 		},
 		{
 			name: "Multiple Invalid usages",
@@ -756,7 +669,7 @@ func TestValidateLeafKeyUsage(t *testing.T) {
 				KeyUsage:   x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment | x509.KeyUsageDataEncipherment | x509.KeyUsageKeyAgreement | x509.KeyUsageCertSign | x509.KeyUsageCRLSign | x509.KeyUsageEncipherOnly | x509.KeyUsageDecipherOnly | x509.KeyUsageEncipherOnly | x509.KeyUsageDecipherOnly,
 				Extensions: extensions,
 			},
-			expectedErrMsg: "The certificate with subject \"CN=Test CN\" is invalid. The key usage must be \"Digital Signature\" only, but found \"KeyEncipherment\", \"DataEncipherment\", \"KeyAgreement\", \"CertSign\", \"CRLSign\", \"EncipherOnly\", \"DecipherOnly\"",
+			expectedErrMsg: "the certificate with subject \"CN=Test CN\" is invalid. The key usage must be \"Digital Signature\" only, but found \"KeyEncipherment\", \"DataEncipherment\", \"KeyAgreement\", \"CertSign\", \"CRLSign\", \"EncipherOnly\", \"DecipherOnly\"",
 		},
 	}
 
@@ -773,3 +686,81 @@ func TestValidateLeafKeyUsage(t *testing.T) {
 		})
 	}
 }
+
+var ekuWrongValuesCodeLeafPem = "-----BEGIN CERTIFICATE-----\n" +
+	"MIIC6jCCAdKgAwIBAgIJAKZJHdWFNYPlMA0GCSqGSIb3DQEBCwUAMBAxDjAMBgNV\n" +
+	"BAMMBUhlbGxvMCAXDTIyMDYyNTAzMDEwM1oYDzIxMjIwNjAxMDMwMTAzWjAQMQ4w\n" +
+	"DAYDVQQDDAVIZWxsbzCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAK2t\n" +
+	"EFpNOJkX7B78d9ahTl5MXGWyKIjgfg1PhkYwHKHJWBiqHa1OUewfUG4ouVuaAvJ+\n" +
+	"GPzcxt23/J3jK+3/szrzpBNv1f0vgIa+mqaRQDW2m/wfWw3kpcwxlRcL7GnCeHbv\n" +
+	"gRFDXQW6MhKgGgKdQ5ezV+p01eF+CzMhUe+bZO+mvgxj36MJHzLMFHyh3x4/+z4x\n" +
+	"qRKmj4uUqJ2FJLlQEk92vPE/N3r7rEWa6gd4mBZ+DsZSrCbVPXchS2mCkeg70qxA\n" +
+	"4840qVLZ5eFxtqnTEUNytu3ug/8ydV9VmuT+C5fQYUp3Fl7D1QxHxWYTVTKdenCY\n" +
+	"jxcJHW1cUWZQlgPTLq8CAwEAAaNFMEMwDgYDVR0PAQH/BAQDAgeAMDEGA1UdJQQq\n" +
+	"MCgGCCsGAQUFBwMDBggrBgEFBQcDAQYIKwYBBQUHAwQGCCsGAQUFBwMIMA0GCSqG\n" +
+	"SIb3DQEBCwUAA4IBAQBRfpNRu79i47yp73LWTKrnZRiLC4JAI3I3w5TTx8m2tYkq\n" +
+	"tkSCP3Sn4y6VjKqo9Xtlt/bBLypw7XAOZOUZLEaoCjwRmAwq74VHAxDZO1LfFlKd\n" +
+	"au8G3xhKjc5prOMJ2g4DELOcyDoLDlwYqQ/jfG/t8b0P37yakFVffSzIA7D0BjmS\n" +
+	"OnWrGOJO/IJZjiaTdQkg+n5jk4FNqhwW91em64/M3MOmib3plnl89MgR90kuvQOV\n" +
+	"ctDBylt8M61MgnbzeunAq4aKYJc4IeeIH++g4F3/pqyoC95sAZP+A6+LkmBDOcyE\n" +
+	"5wUmNtUsL9xxKIUCvPR1JtiLNxHrfendWiuJnW1M\n" +
+	"-----END CERTIFICATE-----"
+var ekuWrongValuesCodeLeaf = parseCertificateFromString(ekuWrongValuesCodeLeafPem)
+
+func TestFailEkuWrongValuesCodeLeaf(t *testing.T) {
+	err := validateCodeSigningLeafCertificate(ekuWrongValuesCodeLeaf)
+	assertErrorEqual("certificate with subject \"CN=Hello\": extended key usage must not contain ServerAuth eku", err, t)
+}
+
+var ekuMissingCodeSigningLeafPem = "-----BEGIN CERTIFICATE-----\n" +
+	"MIICzDCCAbSgAwIBAgIJAJtYOfTu82KRMA0GCSqGSIb3DQEBCwUAMBAxDjAMBgNV\n" +
+	"BAMMBUhlbGxvMCAXDTIyMDYyNTAzMTMxM1oYDzIxMjIwNjAxMDMxMzEzWjAQMQ4w\n" +
+	"DAYDVQQDDAVIZWxsbzCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBALQN\n" +
+	"GJKHE6cdcmrHkxXOTawWgYEF1X42IOK7gAXFg+KBPHPw4npDjUclLX0sY3XjBuhT\n" +
+	"wI5DRATSNTV2ba3+DpFuH3D+Hbfjil91AG8XzormUPOOCbZqJxSKYAIZfPQGdUvV\n" +
+	"UBulnbDsije00HoNZ03IvdjxbB/9y6a3qQEvIUaEjaZBH3s/YYQIiEmKu6eDpj3R\n" +
+	"PnUcrP5b7jBMA/Vb8joLM0InzqGPRLPFAPf5womAjxZSsrgyVeA1xSm+6KtXMmaA\n" +
+	"IKYwNVAOnhfqgUk0tlaRyXXji2T1M9w9l5XUA1iNOMcjTUTfFa5KW7c0TLTcK6vW\n" +
+	"Eq1BEXUEw7HP7DQUjycCAwEAAaMnMCUwDgYDVR0PAQH/BAQDAgeAMBMGA1UdJQQM\n" +
+	"MAoGCCsGAQUFBwMJMA0GCSqGSIb3DQEBCwUAA4IBAQCSr6A/YAMd6lisgipR0UCA\n" +
+	"4Ye/1kl0jglT7stLTfftSeXgCKXYlwus9VSpZBtg+RvJkihlLNT6vtsiTMfJUBBc\n" +
+	"jALLKYUQuCw9sReAbfvecIfc2bUve6X8isLWDVnxlC1udx2WG3lIfW2Sgs/dYeZW\n" +
+	"yqLTagK5GLlDfg9gBpHLmQYOmshhI85ObOioUAiWTW+S6mx4Bphgl7dlcUabJxEJ\n" +
+	"MpJJiGPkUUUCuYkp31E7S4JRbSXSkaHefZxB5fvhlbnACeqnOtMG/IKaTjCUemkK\n" +
+	"ZRmJ0Al1PTWs+Dn8zLzexP/LkmQZU/FUMxeat/dAnc2blDbVnAsvcvnutXGHoZH5\n" +
+	"-----END CERTIFICATE-----"
+var ekuMissingCodeSigningLeaf = parseCertificateFromString(ekuMissingCodeSigningLeafPem)
+
+func TestFailEkuMissingCodeSigningLeaf(t *testing.T) {
+	err := validateCodeSigningLeafCertificate(ekuMissingCodeSigningLeaf)
+	assertErrorEqual("certificate with subject \"CN=Hello\": extended key usage must not contain OCSPSigning eku", err, t)
+}
+
+// ---------------- Utility Methods ----------------
+
+func parseCertificateFromString(certPem string) *x509.Certificate {
+	stringAsBytes := []byte(certPem)
+	cert, _ := parseCertificates(stringAsBytes)
+	return cert[0]
+}
+
+func assertErrorEqual(expected string, err error, t *testing.T) {
+	if err == nil || expected != err.Error() {
+		t.Fatalf("Expected error \"%v\" but was \"%v\"", expected, err)
+	}
+}
+
+func readSingleCertificate(path string) (*x509.Certificate, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+	certs, err := parseCertificates(data)
+	if err != nil {
+		return nil, err
+	}
+	if len(certs) == 0 {
+		return nil, errors.New("no certificate in file")
+	}
+	return certs[0], nil
+}

x509/helper.go

@@ -0,0 +1,124 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package x509
+
+import (
+	"bytes"
+	"crypto/x509"
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/notaryproject/notation-core-go/internal/algorithm"
+)
+
+func isSelfSigned(cert *x509.Certificate) (bool, error) {
+	return isIssuedBy(cert, cert)
+}
+
+func isIssuedBy(subject *x509.Certificate, issuer *x509.Certificate) (bool, error) {
+	if err := subject.CheckSignatureFrom(issuer); err != nil {
+		return false, err
+	}
+	return bytes.Equal(issuer.RawSubject, subject.RawIssuer), nil
+}
+
+func validateSigningTime(cert *x509.Certificate, signingTime *time.Time) error {
+	if signingTime != nil && (signingTime.Before(cert.NotBefore) || signingTime.After(cert.NotAfter)) {
+		return fmt.Errorf("certificate with subject %q was invalid at signing time of %s. Certificate is valid from [%s] to [%s]",
+			cert.Subject, signingTime.UTC(), cert.NotBefore.UTC(), cert.NotAfter.UTC())
+	}
+	return nil
+}
+
+func validateCABasicConstraints(cert *x509.Certificate, expectedPathLen int) error {
+	if !cert.BasicConstraintsValid || !cert.IsCA {
+		return fmt.Errorf("certificate with subject %q: ca field in basic constraints must be present, critical, and set to true", cert.Subject)
+	}
+	maxPathLen := cert.MaxPathLen
+	isMaxPathLenPresent := maxPathLen > 0 || (maxPathLen == 0 && cert.MaxPathLenZero)
+	if isMaxPathLenPresent && maxPathLen < expectedPathLen {
+		return fmt.Errorf("certificate with subject %q: expected path length of %d but certificate has path length %d instead", cert.Subject, expectedPathLen, maxPathLen)
+	}
+	return nil
+}
+
+func validateLeafBasicConstraints(cert *x509.Certificate) error {
+	if cert.BasicConstraintsValid && cert.IsCA {
+		return fmt.Errorf("certificate with subject %q: if the basic constraints extension is present, the ca field must be set to false", cert.Subject)
+	}
+	return nil
+}
+
+func validateLeafKeyUsage(cert *x509.Certificate) error {
+	if cert.KeyUsage&x509.KeyUsageDigitalSignature == 0 {
+		return fmt.Errorf("the certificate with subject %q is invalid. The key usage must have the bit positions for \"Digital Signature\" set", cert.Subject)
+	}
+
+	var invalidKeyUsages []string
+	if cert.KeyUsage&x509.KeyUsageKeyEncipherment != 0 {
+		invalidKeyUsages = append(invalidKeyUsages, `"KeyEncipherment"`)
+	}
+	if cert.KeyUsage&x509.KeyUsageDataEncipherment != 0 {
+		invalidKeyUsages = append(invalidKeyUsages, `"DataEncipherment"`)
+	}
+	if cert.KeyUsage&x509.KeyUsageKeyAgreement != 0 {
+		invalidKeyUsages = append(invalidKeyUsages, `"KeyAgreement"`)
+	}
+	if cert.KeyUsage&x509.KeyUsageCertSign != 0 {
+		invalidKeyUsages = append(invalidKeyUsages, `"CertSign"`)
+	}
+	if cert.KeyUsage&x509.KeyUsageCRLSign != 0 {
+		invalidKeyUsages = append(invalidKeyUsages, `"CRLSign"`)
+	}
+	if cert.KeyUsage&x509.KeyUsageEncipherOnly != 0 {
+		invalidKeyUsages = append(invalidKeyUsages, `"EncipherOnly"`)
+	}
+	if cert.KeyUsage&x509.KeyUsageDecipherOnly != 0 {
+		invalidKeyUsages = append(invalidKeyUsages, `"DecipherOnly"`)
+	}
+	if len(invalidKeyUsages) > 0 {
+		return fmt.Errorf("the certificate with subject %q is invalid. The key usage must be \"Digital Signature\" only, but found %s", cert.Subject, strings.Join(invalidKeyUsages, ", "))
+	}
+	return nil
+}
+
+func validateSignatureAlgorithm(cert *x509.Certificate) error {
+	_, err := algorithm.ExtractKeySpec(cert)
+	if err != nil {
+		return fmt.Errorf("certificate with subject %q: %w", cert.Subject, err)
+	}
+	return nil
+}
+
+func ekuToString(eku x509.ExtKeyUsage) string {
+	switch eku {
+	case x509.ExtKeyUsageAny:
+		return "Any"
+	case x509.ExtKeyUsageServerAuth:
+		return "ServerAuth"
+	case x509.ExtKeyUsageClientAuth:
+		return "ClientAuth"
+	case x509.ExtKeyUsageOCSPSigning:
+		return "OCSPSigning"
+	case x509.ExtKeyUsageEmailProtection:
+		return "EmailProtection"
+	case x509.ExtKeyUsageCodeSigning:
+		return "CodeSigning"
+	case x509.ExtKeyUsageTimeStamping:
+		return "Timestamping"
+	default:
+		return fmt.Sprintf("%d", int(eku))
+	}
+}

x509/timestamp_cert_validations.go

@@ -0,0 +1,167 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package x509
+
+import (
+	"bytes"
+	"crypto/x509"
+	"errors"
+	"fmt"
+
+	"github.com/notaryproject/notation-core-go/internal/oid"
+)
+
+// ValidateTimestampingCertChain takes an ordered time stamping certificate
+// chain and validates issuance from leaf to root
+// Validates certificates according to this spec:
+// https://github.com/notaryproject/notaryproject/blob/main/specs/signature-specification.md#certificate-requirements
+func ValidateTimestampingCertChain(certChain []*x509.Certificate) error {
+	if len(certChain) < 1 {
+		return errors.New("certificate chain must contain at least one certificate")
+	}
+
+	// For self-signed signing certificate (not a CA)
+	if len(certChain) == 1 {
+		cert := certChain[0]
+		// check self-signed
+		if err := cert.CheckSignature(cert.SignatureAlgorithm, cert.RawTBSCertificate, cert.Signature); err != nil {
+			return fmt.Errorf("invalid self-signed certificate. subject: %q. Error: %w", cert.Subject, err)
+		}
+		// check self-issued
+		if !bytes.Equal(cert.RawSubject, cert.RawIssuer) {
+			return fmt.Errorf("invalid self-signed certificate. subject: %q. Error: issuer (%s) and subject (%s) are not the same", cert.Subject, cert.Issuer, cert.Subject)
+		}
+		if err := validateTimestampingLeafCertificate(cert); err != nil {
+			return fmt.Errorf("invalid self-signed certificate. Error: %w", err)
+		}
+		return nil
+	}
+
+	for i, cert := range certChain {
+		if i == len(certChain)-1 {
+			selfSigned, selfSignedError := isSelfSigned(cert)
+			if selfSignedError != nil {
+				return fmt.Errorf("root certificate with subject %q is invalid or not self-signed. Certificate chain must end with a valid self-signed root certificate. Error: %v", cert.Subject, selfSignedError)
+			}
+			if !selfSigned {
+				return fmt.Errorf("root certificate with subject %q is not self-signed. Certificate chain must end with a valid self-signed root certificate", cert.Subject)
+			}
+		} else {
+			// This is to avoid extra/redundant multiple root cert at the end
+			// of certificate-chain
+			selfSigned, selfSignedError := isSelfSigned(cert)
+			// not checking selfSignedError != nil here because we expect
+			// a non-nil err. For a non-root certificate, it shouldn't be
+			// self-signed, hence CheckSignatureFrom would return a non-nil
+			// error.
+			if selfSignedError == nil && selfSigned {
+				if i == 0 {
+					return fmt.Errorf("leaf certificate with subject %q is self-signed. Certificate chain must not contain self-signed leaf certificate", cert.Subject)
+				}
+				return fmt.Errorf("intermediate certificate with subject %q is self-signed. Certificate chain must not contain self-signed intermediate certificate", cert.Subject)
+			}
+			parentCert := certChain[i+1]
+			issuedBy, issuedByError := isIssuedBy(cert, parentCert)
+			if issuedByError != nil {
+				return fmt.Errorf("invalid certificates or certificate with subject %q is not issued by %q. Error: %v", cert.Subject, parentCert.Subject, issuedByError)
+			}
+			if !issuedBy {
+				return fmt.Errorf("certificate with subject %q is not issued by %q", cert.Subject, parentCert.Subject)
+			}
+		}
+
+		if i == 0 {
+			if err := validateTimestampingLeafCertificate(cert); err != nil {
+				return err
+			}
+		} else {
+			if err := validateTimestampingCACertificate(cert, i-1); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+func validateTimestampingCACertificate(cert *x509.Certificate, expectedPathLen int) error {
+	if err := validateCABasicConstraints(cert, expectedPathLen); err != nil {
+		return err
+	}
+	return validateTimestampingCAKeyUsage(cert)
+}
+
+func validateTimestampingLeafCertificate(cert *x509.Certificate) error {
+	if err := validateLeafBasicConstraints(cert); err != nil {
+		return err
+	}
+	if err := validateTimestampingLeafKeyUsage(cert); err != nil {
+		return err
+	}
+	if err := validateTimestampingExtendedKeyUsage(cert); err != nil {
+		return err
+	}
+	return validateSignatureAlgorithm(cert)
+}
+
+func validateTimestampingCAKeyUsage(cert *x509.Certificate) error {
+	if err := validateTimestampingKeyUsagePresent(cert); err != nil {
+		return err
+	}
+	if cert.KeyUsage&x509.KeyUsageCertSign == 0 {
+		return fmt.Errorf("certificate with subject %q: key usage must have the bit positions for key cert sign set", cert.Subject)
+	}
+	return nil
+}
+
+func validateTimestampingLeafKeyUsage(cert *x509.Certificate) error {
+	if err := validateTimestampingKeyUsagePresent(cert); err != nil {
+		return err
+	}
+	return validateLeafKeyUsage(cert)
+}
+
+func validateTimestampingKeyUsagePresent(cert *x509.Certificate) error {
+	var hasKeyUsageExtension bool
+	for _, ext := range cert.Extensions {
+		if ext.Id.Equal(oid.KeyUsage) {
+			hasKeyUsageExtension = true
+			break
+		}
+	}
+	if !hasKeyUsageExtension {
+		return fmt.Errorf("certificate with subject %q: key usage extension must be present", cert.Subject)
+	}
+	return nil
+}
+
+func validateTimestampingExtendedKeyUsage(cert *x509.Certificate) error {
+	// RFC 3161 2.3: The corresponding certificate MUST contain only one
+	// instance of the extended key usage field extension. And it MUST be
+	// marked as critical.
+	if len(cert.ExtKeyUsage) != 1 ||
+		cert.ExtKeyUsage[0] != x509.ExtKeyUsageTimeStamping ||
+		len(cert.UnknownExtKeyUsage) != 0 {
+		return fmt.Errorf("timestamp signing certificate with subject %q must have and only have %s as extended key usage", cert.Subject, ekuToString(x509.ExtKeyUsageTimeStamping))
+	}
+	// check if Extended Key Usage extension is marked critical
+	for _, ext := range cert.Extensions {
+		if ext.Id.Equal(oid.ExtKeyUsage) {
+			if !ext.Critical {
+				return fmt.Errorf("timestamp signing certificate with subject %q must have extended key usage extension marked as critical", cert.Subject)
+			}
+			break
+		}
+	}
+	return nil
+}

x509/timestamp_cert_validations_test.go

@@ -0,0 +1,306 @@
+// Copyright The Notary Project Authors.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package x509
+
+import (
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/asn1"
+	"math/big"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/notaryproject/notation-core-go/internal/oid"
+	"github.com/notaryproject/notation-core-go/testhelper"
+)
+
+func TestValidTimestampingChain(t *testing.T) {
+	timestamp_leaf, err := readSingleCertificate("testdata/timestamp_leaf.crt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	timestamp_intermediate, err := readSingleCertificate("testdata/timestamp_intermediate.crt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	timestamp_root, err := readSingleCertificate("testdata/timestamp_root.crt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	certChain := []*x509.Certificate{timestamp_leaf, timestamp_intermediate, timestamp_root}
+	err = ValidateTimestampingCertChain(certChain)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestFailSelfIssuedTimestampingCert(t *testing.T) {
+	chainTuple := testhelper.GetRevokableRSATimestampChain(2)
+	// the leaf certiifcate and the root certificate share the same private key
+	// so the leaf is also self-signed but issuer and subject are different
+	chain := []*x509.Certificate{chainTuple[0].Cert}
+	err := ValidateTimestampingCertChain(chain)
+	assertErrorEqual("invalid self-signed certificate. subject: \"CN=Notation Test Revokable RSA Chain Cert 2,O=Notary,L=Seattle,ST=WA,C=US\". Error: issuer (CN=Notation Test Revokable RSA Chain Cert Root,O=Notary,L=Seattle,ST=WA,C=US) and subject (CN=Notation Test Revokable RSA Chain Cert 2,O=Notary,L=Seattle,ST=WA,C=US) are not the same", err, t)
+}
+
+func TestInvalidTimestampSelfSignedCert(t *testing.T) {
+	cert, err := createSelfSignedCert("valid cert", "valid cert", false)
+	if err != nil {
+		t.Error(err)
+	}
+	certChain := []*x509.Certificate{cert}
+
+	expectPrefix := "invalid self-signed certificate. Error: timestamp signing certificate with subject \"CN=valid cert\" must have and only have Timestamping as extended key usage"
+	err = ValidateTimestampingCertChain(certChain)
+	if !strings.HasPrefix(err.Error(), expectPrefix) {
+		t.Errorf("expected error to start with %q, got %q", expectPrefix, err)
+	}
+}
+
+func TestValidTimestampSelfSignedCert(t *testing.T) {
+	cert, err := createSelfSignedCert("valid cert", "valid cert", true)
+	if err != nil {
+		t.Error(err)
+	}
+	certChain := []*x509.Certificate{cert}
+
+	err = ValidateTimestampingCertChain(certChain)
+	if err != nil {
+		t.Error(err)
+	}
+}
+
+func TestInvalidTimestampingChain(t *testing.T) {
+	timestamp_leaf, err := readSingleCertificate("testdata/timestamp_leaf.crt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	timestamp_intermediate, err := readSingleCertificate("testdata/timestamp_intermediate.crt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	timestamp_root, err := readSingleCertificate("testdata/timestamp_root.crt")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	expectedErr := "certificate chain must contain at least one certificate"
+	err = ValidateTimestampingCertChain([]*x509.Certificate{})
+	assertErrorEqual(expectedErr, err, t)
+
+	certChain := []*x509.Certificate{timestamp_leaf, intermediateCert2, intermediateCert1, rootCert}
+	expectedErr = "invalid certificates or certificate with subject \"CN=DigiCert Timestamp 2023,O=DigiCert\\\\, Inc.,C=US\" is not issued by \"CN=Intermediate2\". Error: crypto/rsa: verification error"
+	err = ValidateTimestampingCertChain(certChain)
+	assertErrorEqual(expectedErr, err, t)
+
+	certChain = []*x509.Certificate{timestamp_leaf}
+	expectedErr = "invalid self-signed certificate. subject: \"CN=DigiCert Timestamp 2023,O=DigiCert\\\\, Inc.,C=US\". Error: crypto/rsa: verification error"
+	err = ValidateTimestampingCertChain(certChain)
+	assertErrorEqual(expectedErr, err, t)
+
+	certChain = []*x509.Certificate{timestamp_leaf, timestamp_intermediate}
+	expectedErr = "root certificate with subject \"CN=DigiCert Trusted G4 RSA4096 SHA256 TimeStamping CA,O=DigiCert\\\\, Inc.,C=US\" is invalid or not self-signed. Certificate chain must end with a valid self-signed root certificate. Error: crypto/rsa: verification error"
+	err = ValidateTimestampingCertChain(certChain)
+	assertErrorEqual(expectedErr, err, t)
+
+	certChain = []*x509.Certificate{timestamp_root, timestamp_root}
+	expectedErr = "leaf certificate with subject \"CN=DigiCert Trusted Root G4,OU=www.digicert.com,O=DigiCert Inc,C=US\" is self-signed. Certificate chain must not contain self-signed leaf certificate"
+	err = ValidateTimestampingCertChain(certChain)
+	assertErrorEqual(expectedErr, err, t)
+
+	certChain = []*x509.Certificate{timestamp_leaf, timestamp_intermediate, timestamp_root, timestamp_root}
+	expectedErr = "intermediate certificate with subject \"CN=DigiCert Trusted Root G4,OU=www.digicert.com,O=DigiCert Inc,C=US\" is self-signed. Certificate chain must not contain self-signed intermediate certificate"
+	err = ValidateTimestampingCertChain(certChain)
+	assertErrorEqual(expectedErr, err, t)
+}
+
+var ekuNonCriticalTimeLeafPem = "-----BEGIN CERTIFICATE-----\n" +
+	"MIIC5TCCAc2gAwIBAgIBATANBgkqhkiG9w0BAQsFADAYMRYwFAYDVQQDDA1JbnRl\n" +
+	"cm1lZGlhdGUyMCAXDTIyMDYzMDE5MjAwNFoYDzMwMjExMDMxMTkyMDA0WjAbMRkw\n" +
+	"FwYDVQQDDBBUaW1lU3RhbXBpbmdMZWFmMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8A\n" +
+	"MIIBCgKCAQEAyx2ispY5C5sQCiLAuCUTp4wv+fpgHwzE4an8eqi+Jrm0tEabTdzP\n" +
+	"IdZFRYPZbgRx+D9DKeN76f+rt51G9gOX77fYWyIXgnVL4UAYNlQj58hqZ0IO22vT\n" +
+	"nIFiDbJoSPuamQaLZNuluiirUwJv1uqSQiEnWHC4LhKwNOo4UHH5S3XkkYRpdFBF\n" +
+	"Tm4uOTaQJA9dfCh+0wbe7ZlEjDiuk1GTSQu69EPIl4IK7aEWqdvk2z1Pg4YkgJZX\n" +
+	"mWzkECNayUiBeHj7lL5ZnyZeki2l77WzXe/j5dgQ9E2+63hfBew+O/XeS/Tm/TyQ\n" +
+	"0P8bQre6vbn9820Cpyg82fd1+5bwYedwVwIDAQABozUwMzAOBgNVHQ8BAf8EBAMC\n" +
+	"B4AwDAYDVR0TAQH/BAIwADATBgNVHSUEDDAKBggrBgEFBQcDCDANBgkqhkiG9w0B\n" +
+	"AQsFAAOCAQEAB9Z80K17p4J3VCqVcKyhgkzzYPoKiBWFThVwxS2+TKY0x4zezSAT\n" +
+	"69Nmf7NkVH4XyvCEUfgdWYst4t41rH3b5MTMOc5/nPeMccDWT0eZRivodF5hFWZd\n" +
+	"2QSFiMHmfUhnglY0ocLbfKeI/QoSGiPyBWO0SK6qOszRi14lP0TpgvgNDtMY/Jj5\n" +
+	"AyINT6o0tyYJvYE23/7ysT3U6pq50M4vOZiSuRys83As/qvlDIDKe8OVlDt6xRvr\n" +
+	"fqdMFWSk6Iay2OCfYcjUbTutMzSI7dvhDivn5FKnNA6M7QD1lqb7V9fymgrQTsth\n" +
+	"We9tUxypXgMjYN74QEHYxEAIfNOTeBppWw==\n" +
+	"-----END CERTIFICATE-----"
+var ekuNonCriticalTimeLeafCert = parseCertificateFromString(ekuNonCriticalTimeLeafPem)
+
+func TestTimestampLeafWithNonCriticalEKU(t *testing.T) {
+	expectedErr := "timestamp signing certificate with subject \"CN=TimeStampingLeaf\" must have extended key usage extension marked as critical"
+	err := validateTimestampingLeafCertificate(ekuNonCriticalTimeLeafCert)
+	assertErrorEqual(expectedErr, err, t)
+}
+
+var ekuWrongValuesTimeLeafPem = "-----BEGIN CERTIFICATE-----\n" +
+	"MIIC6jCCAdKgAwIBAgIJAJOlT2AUbsZiMA0GCSqGSIb3DQEBCwUAMBAxDjAMBgNV\n" +
+	"BAMMBUhlbGxvMCAXDTIyMDYyNTAzMTcyM1oYDzIxMjIwNjAxMDMxNzIzWjAQMQ4w\n" +
+	"DAYDVQQDDAVIZWxsbzCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAOZe\n" +
+	"9zjKWNlFD/HGrkaAI9mh9Fw1gF8S2tphQD/aPd9IS4HJJEQRkKz5oeHj2g1Y6TEk\n" +
+	"plODrKlnoLe+ZFNFFD4xMVV55aQSJDTljCLPwIZt2VewlaAhIImYihOJvJFST1zW\n" +
+	"K2NW4eLxt0awbE/YzL6beH4A6UsrcXcnN0KKiu6YD1/d5TezJoTQBMo6fboltuce\n" +
+	"P/+RMxyqpvip7nyFF3Yrmhumb7DKJrmSfSjdziI5QoUqzqVgqJ8pXMRb3ZOKb499\n" +
+	"d9RRxGkox93iOdSSlaP3FEl8VK9KqnD+MNhjVZbeYTfjm9UVdp91VLP1E/yfMXz+\n" +
+	"fZhYkublK6v3GWSEcb0CAwEAAaNFMEMwDgYDVR0PAQH/BAQDAgeAMDEGA1UdJQQq\n" +
+	"MCgGCCsGAQUFBwMIBggrBgEFBQcDAQYIKwYBBQUHAwQGCCsGAQUFBwMIMA0GCSqG\n" +
+	"SIb3DQEBCwUAA4IBAQCaQZ+ws93F1azT6SKBYvBRBCj07+2DtNI83Q53GxrVy2vU\n" +
+	"rP1ULX7beY87amy6kQcqnQ0QSaoLK+CDL88pPxR2PBzCauz70rMRY8O/KrrLcfwd\n" +
+	"D5HM9DcbneqXQyfh0ZQpt0wK5wux0MFh2sAEv76jgYBMHq2zc+19skAW/oBtTUty\n" +
+	"i/IdOVeO589KXwJzEJmKiswN9zKo9KGgAlKS05zohjv40AOCAs+8Q2lOJjRMq4Ji\n" +
+	"z21qor5e/5+NnGY+2p4A7PbN+QnDdRC3y16dESRN50o5x6CwUWQO74+uRjrAWYCm\n" +
+	"f/Y7qdOf5zZbY21n8KnLcFOsKhwv4t40Y/LQqN/L\n" +
+	"-----END CERTIFICATE-----"
+var ekuWrongValuesTimeLeaf = parseCertificateFromString(ekuWrongValuesTimeLeafPem)
+
+func TestFailEkuWrongValuesTimeLeaf(t *testing.T) {
+	err := validateTimestampingLeafCertificate(ekuWrongValuesTimeLeaf)
+	assertErrorEqual("timestamp signing certificate with subject \"CN=Hello\" must have and only have Timestamping as extended key usage", err, t)
+}
+
+var ekuMissingTimestampingLeafPem = "-----BEGIN CERTIFICATE-----\n" +
+	"MIICzDCCAbSgAwIBAgIJAJtYOfTu82KRMA0GCSqGSIb3DQEBCwUAMBAxDjAMBgNV\n" +
+	"BAMMBUhlbGxvMCAXDTIyMDYyNTAzMTMxM1oYDzIxMjIwNjAxMDMxMzEzWjAQMQ4w\n" +
+	"DAYDVQQDDAVIZWxsbzCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBALQN\n" +
+	"GJKHE6cdcmrHkxXOTawWgYEF1X42IOK7gAXFg+KBPHPw4npDjUclLX0sY3XjBuhT\n" +
+	"wI5DRATSNTV2ba3+DpFuH3D+Hbfjil91AG8XzormUPOOCbZqJxSKYAIZfPQGdUvV\n" +
+	"UBulnbDsije00HoNZ03IvdjxbB/9y6a3qQEvIUaEjaZBH3s/YYQIiEmKu6eDpj3R\n" +
+	"PnUcrP5b7jBMA/Vb8joLM0InzqGPRLPFAPf5womAjxZSsrgyVeA1xSm+6KtXMmaA\n" +
+	"IKYwNVAOnhfqgUk0tlaRyXXji2T1M9w9l5XUA1iNOMcjTUTfFa5KW7c0TLTcK6vW\n" +
+	"Eq1BEXUEw7HP7DQUjycCAwEAAaMnMCUwDgYDVR0PAQH/BAQDAgeAMBMGA1UdJQQM\n" +
+	"MAoGCCsGAQUFBwMJMA0GCSqGSIb3DQEBCwUAA4IBAQCSr6A/YAMd6lisgipR0UCA\n" +
+	"4Ye/1kl0jglT7stLTfftSeXgCKXYlwus9VSpZBtg+RvJkihlLNT6vtsiTMfJUBBc\n" +
+	"jALLKYUQuCw9sReAbfvecIfc2bUve6X8isLWDVnxlC1udx2WG3lIfW2Sgs/dYeZW\n" +
+	"yqLTagK5GLlDfg9gBpHLmQYOmshhI85ObOioUAiWTW+S6mx4Bphgl7dlcUabJxEJ\n" +
+	"MpJJiGPkUUUCuYkp31E7S4JRbSXSkaHefZxB5fvhlbnACeqnOtMG/IKaTjCUemkK\n" +
+	"ZRmJ0Al1PTWs+Dn8zLzexP/LkmQZU/FUMxeat/dAnc2blDbVnAsvcvnutXGHoZH5\n" +
+	"-----END CERTIFICATE-----"
+var ekuMissingTimestampingLeaf = parseCertificateFromString(ekuMissingTimestampingLeafPem)
+
+func TestFailEkuMissingTimestampingLeaf(t *testing.T) {
+	err := validateTimestampingLeafCertificate(ekuMissingTimestampingLeaf)
+	assertErrorEqual("timestamp signing certificate with subject \"CN=Hello\" must have and only have Timestamping as extended key usage", err, t)
+}
+
+func TestTimestampingFailNoBasicConstraintsCa(t *testing.T) {
+	err := validateTimestampingCACertificate(noBasicConstraintsCa, 3)
+	assertErrorEqual("certificate with subject \"CN=Hello\": ca field in basic constraints must be present, critical, and set to true", err, t)
+}
+
+func TestTimestampingFailKuMissingCa(t *testing.T) {
+	err := validateTimestampingCACertificate(kuMissingCa, 3)
+	assertErrorEqual("certificate with subject \"CN=Hello\": key usage extension must be present", err, t)
+}
+
+func TestTimestampingFailInvalidPathLenCa(t *testing.T) {
+	err := validateTimestampingCACertificate(rootCert, 3)
+	assertErrorEqual("certificate with subject \"CN=Root\": expected path length of 3 but certificate has path length 2 instead", err, t)
+}
+
+func TestTimestampingFailKuNotCertSignCa(t *testing.T) {
+	err := validateTimestampingCACertificate(kuNotCertSignCa, 3)
+	assertErrorEqual("certificate with subject \"CN=Hello\": key usage must have the bit positions for key cert sign set", err, t)
+}
+
+func TestTimestampingFailWrongExtendedKeyUsage(t *testing.T) {
+	err := validateTimestampingLeafCertificate(validNoOptionsLeaf)
+	assertErrorEqual("timestamp signing certificate with subject \"CN=Hello\" must have and only have Timestamping as extended key usage", err, t)
+}
+
+func TestValidateTimestampingLeafCertificate(t *testing.T) {
+	err := validateTimestampingLeafCertificate(caTrueLeaf)
+	assertErrorEqual("certificate with subject \"CN=Hello\": if the basic constraints extension is present, the ca field must be set to false", err, t)
+
+	err = validateTimestampingLeafCertificate(kuNoDigitalSignatureLeaf)
+	assertErrorEqual("the certificate with subject \"CN=Hello\" is invalid. The key usage must have the bit positions for \"Digital Signature\" set", err, t)
+
+	cert := &x509.Certificate{
+		Subject:  pkix.Name{CommonName: "Test CN"},
+		KeyUsage: x509.KeyUsageDigitalSignature,
+	}
+	err = validateTimestampingLeafCertificate(cert)
+	assertErrorEqual("certificate with subject \"CN=Test CN\": key usage extension must be present", err, t)
+}
+
+func TestEkuToString(t *testing.T) {
+	if ekuToString(x509.ExtKeyUsageAny) != "Any" {
+		t.Fatalf("expected Any")
+	}
+	if ekuToString(x509.ExtKeyUsageClientAuth) != "ClientAuth" {
+		t.Fatalf("expected ClientAuth")
+	}
+	if ekuToString(x509.ExtKeyUsageEmailProtection) != "EmailProtection" {
+		t.Fatalf("expected EmailProtection")
+	}
+	if ekuToString(x509.ExtKeyUsageCodeSigning) != "CodeSigning" {
+		t.Fatalf("expected CodeSigning")
+	}
+	if ekuToString(x509.ExtKeyUsageIPSECUser) != "7" {
+		t.Fatalf("expected 7")
+	}
+}
+
+func createSelfSignedCert(subject string, issuer string, isTimestamp bool) (*x509.Certificate, error) {
+	priv, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		return nil, err
+	}
+
+	template := &x509.Certificate{
+		SerialNumber: big.NewInt(1),
+		Subject:      pkix.Name{CommonName: subject},
+		NotBefore:    time.Now(),
+		NotAfter:     time.Now().Add(365 * 24 * time.Hour),
+		KeyUsage:     x509.KeyUsageDigitalSignature,
+	}
+
+	if isTimestamp {
+		oids := []asn1.ObjectIdentifier{{1, 3, 6, 1, 5, 5, 7, 3, 8}}
+		value, err := asn1.Marshal(oids)
+		if err != nil {
+			return nil, err
+		}
+		template.ExtraExtensions = []pkix.Extension{{
+			Id:       oid.ExtKeyUsage,
+			Critical: true,
+			Value:    value,
+		}}
+		template.ExtKeyUsage = []x509.ExtKeyUsage{x509.ExtKeyUsageTimeStamping}
+	}
+
+	parentTemplate := &x509.Certificate{
+		SerialNumber: big.NewInt(2),
+		Subject:      pkix.Name{CommonName: issuer},
+		NotBefore:    time.Now(),
+		NotAfter:     time.Now().Add(365 * 24 * time.Hour),
+		KeyUsage:     x509.KeyUsageCertSign,
+	}
+
+	certDER, err := x509.CreateCertificate(rand.Reader, template, parentTemplate, &priv.PublicKey, priv)
+	if err != nil {
+		return nil, err
+	}
+
+	return x509.ParseCertificate(certDER)
+}