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

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

.github/workflows/reusable-build.yml

@@ -24,7 +24,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go-version: ["1.22", "1.23"]
+        go-version: ["1.23", "1.24"]
       fail-fast: true
     steps:
       - name: Checkout

.github/workflows/reusable-codeql.yml

@@ -26,7 +26,7 @@ jobs:
       security-events: write
     strategy:
       matrix:
-        go-version: ["1.22", "1.23"]
+        go-version: ["1.23", "1.24"]
       fail-fast: false
     steps:
       - name: Checkout repository

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

@@ -23,13 +23,13 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
       - name: Check license header
-        uses: apache/skywalking-eyes/header@cd7b195c51fd3d6ad52afceb760719ddc6b3ee91
+        uses: apache/skywalking-eyes/header@5c5b974209f0de5d905f37deb69369068ebfc15c
 
         with:
           mode: check
           config: .github/licenserc.yml
       - name: Check dependencies license
-        uses: apache/skywalking-eyes/dependency@cd7b195c51fd3d6ad52afceb760719ddc6b3ee91
+        uses: apache/skywalking-eyes/dependency@5c5b974209f0de5d905f37deb69369068ebfc15c
         with:
           config: .github/licenserc.yml
           flags:

CODEOWNERS

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

MAINTAINERS

@@ -10,11 +10,13 @@ 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)
 Rakesh Gariganti <garigant@amazon.com> (@rgnote)
 
 # Emeritus Org Maintainers (in alphabetical order)
 Justin Cormack <justin.cormack@docker.com> (@justincormack)
-Steve Lasker <StevenLasker@hotmail.com> (@stevelasker)
+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

go.mod

@@ -1,13 +1,13 @@
 module github.com/notaryproject/notation-core-go
 
-go 1.22
+go 1.23.0
 
 require (
-	github.com/fxamacker/cbor/v2 v2.7.0
-	github.com/golang-jwt/jwt/v4 v4.5.1
-	github.com/notaryproject/tspclient-go v1.0.0-rc.1
+	github.com/fxamacker/cbor/v2 v2.8.0
+	github.com/golang-jwt/jwt/v4 v4.5.2
+	github.com/notaryproject/tspclient-go v1.0.0
 	github.com/veraison/go-cose v1.3.0
-	golang.org/x/crypto v0.29.0
+	golang.org/x/crypto v0.37.0
 )
 
 require github.com/x448/float16 v0.8.4 // indirect

go.sum

@@ -1,12 +1,12 @@
-github.com/fxamacker/cbor/v2 v2.7.0 h1:iM5WgngdRBanHcxugY4JySA0nk1wZorNOpTgCMedv5E=
-github.com/fxamacker/cbor/v2 v2.7.0/go.mod h1:pxXPTn3joSm21Gbwsv0w9OSA2y1HFR9qXEeXQVeNoDQ=
-github.com/golang-jwt/jwt/v4 v4.5.1 h1:JdqV9zKUdtaa9gdPlywC3aeoEsR681PlKC+4F5gQgeo=
-github.com/golang-jwt/jwt/v4 v4.5.1/go.mod h1:m21LjoU+eqJr34lmDMbreY2eSTRJ1cv77w39/MY0Ch0=
-github.com/notaryproject/tspclient-go v1.0.0-rc.1 h1:KcHxlqg6Adt4kzGLw012i0YMLlwGwToiR129c6IQ7Ys=
-github.com/notaryproject/tspclient-go v1.0.0-rc.1/go.mod h1:LGyA/6Kwd2FlM0uk8Vc5il3j0CddbWSHBj/4kxQDbjs=
+github.com/fxamacker/cbor/v2 v2.8.0 h1:fFtUGXUzXPHTIUdne5+zzMPTfffl3RD5qYnkY40vtxU=
+github.com/fxamacker/cbor/v2 v2.8.0/go.mod h1:vM4b+DJCtHn+zz7h3FFp/hDAI9WNWCsZj23V5ytsSxQ=
+github.com/golang-jwt/jwt/v4 v4.5.2 h1:YtQM7lnr8iZ+j5q71MGKkNw9Mn7AjHM68uc9g5fXeUI=
+github.com/golang-jwt/jwt/v4 v4.5.2/go.mod h1:m21LjoU+eqJr34lmDMbreY2eSTRJ1cv77w39/MY0Ch0=
+github.com/notaryproject/tspclient-go v1.0.0 h1:AwQ4x0gX8IHnyiZB1tggpn5NFqHpTEm1SDX8YNv4Dg4=
+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 v0.29.0 h1:L5SG1JTTXupVV3n6sUqMTeWbjAyfPwoda2DLX8J8FrQ=
-golang.org/x/crypto v0.29.0/go.mod h1:+F4F4N5hv6v38hfeYwTdx20oUvLLc+QfrE9Ax9HtgRg=
+golang.org/x/crypto v0.37.0 h1:kJNSjF/Xp7kU0iB2Z+9viTPMW4EqqsrywMXLJOOsXSE=
+golang.org/x/crypto v0.37.0/go.mod h1:vg+k43peMZ0pUMhYmVAWysMK35e6ioLh3wB8ZCAfbVc=

revocation/crl/errors.go

@@ -17,3 +17,6 @@ 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

@@ -18,6 +18,7 @@ package crl
 import (
 	"context"
 	"crypto/x509"
+	"crypto/x509/pkix"
 	"encoding/asn1"
 	"errors"
 	"fmt"
@@ -25,6 +26,10 @@ import (
 	"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
@@ -84,9 +89,8 @@ func (f *HTTPFetcher) Fetch(ctx context.Context, url string) (*Bundle, error) {
 	if f.Cache != nil {
 		bundle, err := f.Cache.Get(ctx, url)
 		if err == nil {
-			// check expiry
-			nextUpdate := bundle.BaseCRL.NextUpdate
-			if !nextUpdate.IsZero() && !time.Now().After(nextUpdate) {
+			// 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 {
@@ -109,6 +113,11 @@ func (f *HTTPFetcher) Fetch(ctx context.Context, url string) (*Bundle, error) {
 	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
@@ -117,19 +126,109 @@ func (f *HTTPFetcher) fetch(ctx context.Context, url string) (*Bundle, error) {
 		return nil, err
 	}
 
-	// check delta CRL
-	// TODO: support delta CRL https://github.com/notaryproject/notation-core-go/issues/228
-	for _, ext := range base.Extensions {
-		if ext.Id.Equal(oidFreshestCRL) {
-			return nil, errors.New("delta CRL is not supported")
-		}
+	// 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,
+		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)

revocation/crl/fetcher_test.go

@@ -19,11 +19,13 @@ import (
 	"crypto/rand"
 	"crypto/x509"
 	"crypto/x509/pkix"
+	"encoding/pem"
 	"errors"
 	"fmt"
 	"io"
 	"math/big"
 	"net/http"
+	"os"
 	"strings"
 	"sync"
 	"testing"
@@ -78,7 +80,7 @@ func TestFetch(t *testing.T) {
 
 	t.Run("fetch without cache", func(t *testing.T) {
 		httpClient := &http.Client{
-			Transport: expectedRoundTripperMock{Body: baseCRL.Raw},
+			Transport: &expectedRoundTripperMock{Body: baseCRL.Raw},
 		}
 		f, err := NewHTTPFetcher(httpClient)
 		if err != nil {
@@ -134,7 +136,7 @@ func TestFetch(t *testing.T) {
 	t.Run("cache miss", func(t *testing.T) {
 		c := &memoryCache{}
 		httpClient := &http.Client{
-			Transport: expectedRoundTripperMock{Body: baseCRL.Raw},
+			Transport: &expectedRoundTripperMock{Body: baseCRL.Raw},
 		}
 		f, err := NewHTTPFetcher(httpClient)
 		if err != nil {
@@ -177,7 +179,7 @@ func TestFetch(t *testing.T) {
 
 		// fetch the expired CRL
 		httpClient := &http.Client{
-			Transport: expectedRoundTripperMock{Body: baseCRL.Raw},
+			Transport: &expectedRoundTripperMock{Body: baseCRL.Raw},
 		}
 		f, err := NewHTTPFetcher(httpClient)
 		if err != nil {
@@ -195,46 +197,13 @@ func TestFetch(t *testing.T) {
 		}
 	})
 
-	t.Run("delta CRL is not supported", func(t *testing.T) {
-		c := &memoryCache{}
-		// prepare a CRL with refresh CRL extension
-		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),
-			ExtraExtensions: []pkix.Extension{
-				{
-					Id:    oidFreshestCRL,
-					Value: []byte{0x01, 0x02, 0x03},
-				},
-			},
-		}, certChain[1].Cert, certChain[1].PrivateKey)
-		if err != nil {
-			t.Fatalf("failed to create base CRL: %v", err)
-		}
-
-		httpClient := &http.Client{
-			Transport: expectedRoundTripperMock{Body: expiredCRLBytes},
-		}
-		f, err := NewHTTPFetcher(httpClient)
-		if err != nil {
-			t.Errorf("NewHTTPFetcher() error = %v, want nil", err)
-		}
-		f.Cache = c
-		f.DiscardCacheError = true
-		_, err = f.Fetch(context.Background(), uncachedURL)
-		if !strings.Contains(err.Error(), "delta CRL is not supported") {
-			t.Errorf("Fetcher.Fetch() error = %v, want delta CRL is not supported", err)
-		}
-	})
-
 	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},
+			Transport: &expectedRoundTripperMock{Body: baseCRL.Raw},
 		}
 		f, err := NewHTTPFetcher(httpClient)
 		if err != nil {
@@ -256,7 +225,7 @@ func TestFetch(t *testing.T) {
 			GetError: errors.New("cache error"),
 		}
 		httpClient := &http.Client{
-			Transport: expectedRoundTripperMock{Body: baseCRL.Raw},
+			Transport: &expectedRoundTripperMock{Body: baseCRL.Raw},
 		}
 		f, err := NewHTTPFetcher(httpClient)
 		if err != nil {
@@ -276,7 +245,7 @@ func TestFetch(t *testing.T) {
 			SetError: errors.New("cache error"),
 		}
 		httpClient := &http.Client{
-			Transport: expectedRoundTripperMock{Body: baseCRL.Raw},
+			Transport: &expectedRoundTripperMock{Body: baseCRL.Raw},
 		}
 		f, err := NewHTTPFetcher(httpClient)
 		if err != nil {
@@ -289,6 +258,217 @@ func TestFetch(t *testing.T) {
 			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) {
@@ -343,7 +523,7 @@ func TestDownload(t *testing.T) {
 
 	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)},
+			Transport: &expectedRoundTripperMock{Body: make([]byte, maxCRLSize+1)},
 		})
 		if err == nil {
 			t.Fatal("expected error")
@@ -352,7 +532,7 @@ func TestDownload(t *testing.T) {
 
 	t.Run("invalid crl", func(t *testing.T) {
 		_, err := fetchCRL(context.Background(), "http://localhost.test", &http.Client{
-			Transport: expectedRoundTripperMock{Body: []byte("invalid crl")},
+			Transport: &expectedRoundTripperMock{Body: []byte("invalid crl")},
 		})
 		if err == nil {
 			t.Fatal("expected error")
@@ -395,14 +575,24 @@ func (r errorReaderMock) Close() error {
 }
 
 type expectedRoundTripperMock struct {
-	Body []byte
+	Body            []byte
+	SecondRoundBody []byte
+	count           int
 }
 
-func (rt expectedRoundTripperMock) RoundTrip(req *http.Request) (*http.Response, error) {
+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.Body)),
+		Body:       io.NopCloser(bytes.NewBuffer(rt.SecondRoundBody)),
 	}, nil
 }
 

revocation/crl/testdata/certificateWith2DeltaCRL.cer

@@ -0,0 +1,32 @@
+-----BEGIN CERTIFICATE-----
+MIIFdTCCA92gAwIBAgIUaHnHWrIVx0qzAZIwvELkQUEs+3cwDQYJKoZIhvcNAQEL
+BQAwYTEjMCEGCgmSJomT8ixkAQEME2MtMG53d296cXZhd3ZhbzNlY2gxFTATBgNV
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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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+-----END CERTIFICATE-----

revocation/crl/testdata/certificateWithIncompleteFreshestCRL2.cer

@@ -0,0 +1,22 @@
+-----BEGIN CERTIFICATE-----
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+2WF1FNI5WQgKNZQ=
+-----END CERTIFICATE-----

revocation/crl/testdata/certificateWithNonURIDeltaCRL.cer

@@ -0,0 +1,22 @@
+-----BEGIN CERTIFICATE-----
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+A+LwN2MBWdlhdRTSOVkICjWU
+-----END CERTIFICATE-----

revocation/crl/testdata/certificateWithZeroDeltaCRLURL.cer

@@ -0,0 +1,25 @@
+-----BEGIN CERTIFICATE-----
+MIIENTCCAp2gAwIBAgIUaHnHWrIVx0qzAZIwvELkQUEs+3cwDQYJKoZIhvcNAQEL
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+c3RhcnQwHhcNMjQxMTI1MDc1NzI3WhcNMjYxMTI1MDc1NzI2WjAYMRYwFAYDVQQD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+-----END CERTIFICATE-----

revocation/internal/crl/crl.go

@@ -21,10 +21,32 @@ import (
 	"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 (
@@ -36,6 +58,10 @@ var (
 	// 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}
@@ -86,9 +112,10 @@ func CertCheckStatus(ctx context.Context, cert, issuer *x509.Certificate, opts C
 	}
 
 	var (
-		serverResults = make([]*result.ServerResult, 0, len(cert.CRLDistributionPoints))
-		lastErr       error
-		crlURL        string
+		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
@@ -105,12 +132,28 @@ func CertCheckStatus(ctx context.Context, cert, issuer *x509.Certificate, opts C
 			break
 		}
 
-		if err = validate(bundle.BaseCRL, issuer); err != nil {
+		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.BaseCRL, opts.SigningTime, crlURL)
+		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
@@ -153,7 +196,44 @@ func Supported(cert *x509.Certificate) bool {
 	return cert != nil && len(cert.CRLDistributionPoints) > 0
 }
 
-func validate(crl *x509.RevocationList, issuer *x509.Certificate) error {
+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)
@@ -170,12 +250,12 @@ func validate(crl *x509.RevocationList, issuer *x509.Certificate) error {
 
 	for _, ext := range crl.Extensions {
 		switch {
-		case ext.Id.Equal(oidFreshestCRL):
-			return errors.New("delta CRL is not supported")
 		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)
@@ -188,16 +268,43 @@ func validate(crl *x509.RevocationList, issuer *x509.Certificate) error {
 }
 
 // checkRevocation checks if the certificate is revoked or not
-func checkRevocation(cert *x509.Certificate, baseCRL *x509.RevocationList, signingTime time.Time, crlURL string) (*result.ServerResult, error) {
+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 baseCRL == 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")
 	}
 
-	for _, revocationEntry := range baseCRL.RevokedCertificateEntries {
+	// 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 {
@@ -209,17 +316,38 @@ func checkRevocation(cert *x509.Certificate, baseCRL *x509.RevocationList, signi
 				signingTime.Before(extensions.invalidityDate) {
 				// signing time is before the invalidity date which means the
 				// certificate is not revoked at the time of signing.
-				break
+				return &result.ServerResult{
+					Result:           result.ResultOK,
+					Server:           crlURL,
+					RevocationMethod: result.RevocationMethodCRL,
+				}, nil
 			}
 
-			// revoked
-			return &result.ServerResult{
-				Result:           result.ResultRevoked,
-				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,
@@ -233,7 +361,7 @@ type entryExtensions struct {
 	invalidityDate time.Time
 }
 
-func parseEntryExtensions(entry x509.RevocationListEntry) (entryExtensions, error) {
+func parseEntryExtensions(entry *x509.RevocationListEntry) (entryExtensions, error) {
 	var extensions entryExtensions
 	for _, ext := range entry.Extensions {
 		switch {

revocation/internal/crl/crl_test.go

@@ -203,38 +203,6 @@ func TestCertCheckStatus(t *testing.T) {
 		}
 	})
 
-	t.Run("CRL with delta CRL is not checked", func(t *testing.T) {
-		memoryCache := &memoryCache{}
-
-		crlBytes, err := x509.CreateRevocationList(rand.Reader, &x509.RevocationList{
-			NextUpdate: time.Now().Add(time.Hour),
-			Number:     big.NewInt(20240720),
-			ExtraExtensions: []pkix.Extension{
-				{
-					Id:       oidFreshestCRL,
-					Critical: false,
-				},
-			},
-		}, issuerCert, issuerKey)
-		if err != nil {
-			t.Fatal(err)
-		}
-		fetcher, err := crlutils.NewHTTPFetcher(
-			&http.Client{Transport: expectedRoundTripperMock{Body: crlBytes}},
-		)
-		if err != nil {
-			t.Fatal(err)
-		}
-		fetcher.Cache = memoryCache
-		fetcher.DiscardCacheError = true
-		r := CertCheckStatus(context.Background(), chain[0].Cert, issuerCert, CertCheckStatusOptions{
-			Fetcher: fetcher,
-		})
-		if !strings.Contains(r.ServerResults[0].Error.Error(), "delta CRL is not supported") {
-			t.Fatalf("unexpected error, got %v, expected %v", r.ServerResults[0].Error, "delta CRL is not supported")
-		}
-	})
-
 	memoryCache := &memoryCache{}
 
 	// create a stale CRL
@@ -328,6 +296,40 @@ func TestCertCheckStatus(t *testing.T) {
 			t.Fatalf("expected OK, got %s", r.Result)
 		}
 	})
+
+	t.Run("freshest CRL from certificate extension is not supported", func(t *testing.T) {
+		chain[0].Cert.Extensions = []pkix.Extension{
+			{
+				Id: oidFreshestCRL,
+			},
+		}
+
+		crlBytes, err := x509.CreateRevocationList(rand.Reader, &x509.RevocationList{
+			NextUpdate: time.Now().Add(time.Hour),
+			Number:     big.NewInt(20240720),
+		}, issuerCert, issuerKey)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		fetcher, err := crlutils.NewHTTPFetcher(
+			&http.Client{Transport: expectedRoundTripperMock{Body: crlBytes}},
+		)
+		if err != nil {
+			t.Fatal(err)
+		}
+		fetcher.DiscardCacheError = true
+		r := CertCheckStatus(context.Background(), chain[0].Cert, issuerCert, CertCheckStatusOptions{
+			Fetcher: fetcher,
+		})
+		if r.Result != result.ResultUnknown {
+			t.Fatalf("expected Unknown, got %s", r.Result)
+		}
+		expectedErrorMsg := "freshest CRL from certificate extension is not supported"
+		if r.ServerResults[0].Error == nil || r.ServerResults[0].Error.Error() != expectedErrorMsg {
+			t.Fatalf("expected error %q, got %v", expectedErrorMsg, r.ServerResults[0].Error)
+		}
+	})
 }
 
 func TestValidate(t *testing.T) {
@@ -349,7 +351,7 @@ func TestValidate(t *testing.T) {
 			t.Fatal(err)
 		}
 
-		if err := validate(crl, issuerCert); err == nil {
+		if err := validateCRL(crl, issuerCert); err == nil {
 			t.Fatal("expected error")
 		}
 	})
@@ -359,7 +361,7 @@ func TestValidate(t *testing.T) {
 			NextUpdate: time.Now().Add(time.Hour),
 		}
 
-		if err := validate(crl, &x509.Certificate{}); err == nil {
+		if err := validateCRL(crl, &x509.Certificate{}); err == nil {
 			t.Fatal("expected error")
 		}
 	})
@@ -390,7 +392,7 @@ func TestValidate(t *testing.T) {
 			},
 		}
 
-		if err := validate(crl, issuerCert); err == nil {
+		if err := validateCRL(crl, issuerCert); err == nil {
 			t.Fatal("expected error")
 		}
 	})
@@ -419,37 +421,215 @@ func TestValidate(t *testing.T) {
 			t.Fatal(err)
 		}
 
-		if err := validate(crl, issuerCert); err != nil {
+		if err := validateCRL(crl, issuerCert); err != nil {
 			t.Fatal(err)
 		}
 	})
 
-	t.Run("delta CRL is not supported", func(t *testing.T) {
-		chain := testhelper.GetRevokableRSAChainWithRevocations(1, false, true)
-		issuerCert := chain[0].Cert
-		issuerKey := chain[0].PrivateKey
+	chain := testhelper.GetRevokableRSAChainWithRevocations(1, false, true)
+	issuerCert := chain[0].Cert
+	issuerKey := chain[0].PrivateKey
 
-		crlBytes, err := x509.CreateRevocationList(rand.Reader, &x509.RevocationList{
+	crlBytes, err := x509.CreateRevocationList(rand.Reader, &x509.RevocationList{
+		NextUpdate: time.Now().Add(time.Hour),
+		Number:     big.NewInt(20240720),
+	}, issuerCert, issuerKey)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	crl, err := x509.ParseRevocationList(crlBytes)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	t.Run("valid crl and delta crl", func(t *testing.T) {
+		deltaCRLIndicator := big.NewInt(20240720)
+		deltaCRLIndicatorBytes, err := asn1.Marshal(deltaCRLIndicator)
+		if err != nil {
+			t.Fatal(err)
+		}
+		deltaCRLBytes, err := x509.CreateRevocationList(rand.Reader, &x509.RevocationList{
 			NextUpdate: time.Now().Add(time.Hour),
-			Number:     big.NewInt(20240720),
+			Number:     big.NewInt(20240721),
 			ExtraExtensions: []pkix.Extension{
 				{
-					Id:       oidFreshestCRL,
-					Critical: false,
+					Id:       oidDeltaCRLIndicator,
+					Critical: true,
+					Value:    deltaCRLIndicatorBytes,
 				},
 			},
 		}, issuerCert, issuerKey)
 		if err != nil {
 			t.Fatal(err)
 		}
-
-		crl, err := x509.ParseRevocationList(crlBytes)
+		deltaCRL, err := x509.ParseRevocationList(deltaCRLBytes)
 		if err != nil {
 			t.Fatal(err)
 		}
+		bundle := &crlutils.Bundle{
+			BaseCRL:  crl,
+			DeltaCRL: deltaCRL,
+		}
+		if err := validate(bundle, issuerCert); err != nil {
+			t.Fatal(err)
+		}
+	})
 
-		if err := validate(crl, issuerCert); err.Error() != "delta CRL is not supported" {
-			t.Fatalf("got %v, expected delta CRL is not supported", err)
+	t.Run("invalid delta crl", func(t *testing.T) {
+		deltaCRLIndicator := big.NewInt(20240720)
+		deltaCRLIndicatorBytes, err := asn1.Marshal(deltaCRLIndicator)
+		if err != nil {
+			t.Fatal(err)
+		}
+		deltaCRLBytes, err := x509.CreateRevocationList(rand.Reader, &x509.RevocationList{
+			Number: big.NewInt(20240721),
+			ExtraExtensions: []pkix.Extension{
+				{
+					Id:       oidDeltaCRLIndicator,
+					Critical: true,
+					Value:    deltaCRLIndicatorBytes,
+				},
+			},
+		}, issuerCert, issuerKey)
+		if err != nil {
+			t.Fatal(err)
+		}
+		deltaCRL, err := x509.ParseRevocationList(deltaCRLBytes)
+		if err != nil {
+			t.Fatal(err)
+		}
+		bundle := &crlutils.Bundle{
+			BaseCRL:  crl,
+			DeltaCRL: deltaCRL,
+		}
+		err = validate(bundle, issuerCert)
+		expectedErrorMsg := "failed to validate delta CRL: CRL NextUpdate is not set"
+		if err == nil || err.Error() != expectedErrorMsg {
+			t.Fatalf("expected error %q, got %v", expectedErrorMsg, err)
+		}
+	})
+
+	t.Run("invalid delta crl number", func(t *testing.T) {
+		deltaCRLIndicator := big.NewInt(20240720)
+		deltaCRLIndicatorBytes, err := asn1.Marshal(deltaCRLIndicator)
+		if err != nil {
+			t.Fatal(err)
+		}
+		deltaCRLBytes, err := x509.CreateRevocationList(rand.Reader, &x509.RevocationList{
+			NextUpdate: time.Now().Add(time.Hour),
+			Number:     big.NewInt(20240719),
+			ExtraExtensions: []pkix.Extension{
+				{
+					Id:       oidDeltaCRLIndicator,
+					Critical: true,
+					Value:    deltaCRLIndicatorBytes,
+				},
+			},
+		}, issuerCert, issuerKey)
+		if err != nil {
+			t.Fatal(err)
+		}
+		deltaCRL, err := x509.ParseRevocationList(deltaCRLBytes)
+		if err != nil {
+			t.Fatal(err)
+		}
+		bundle := &crlutils.Bundle{
+			BaseCRL:  crl,
+			DeltaCRL: deltaCRL,
+		}
+		err = validate(bundle, issuerCert)
+		expectedErrorMsg := "delta CRL number 20240719 is not greater than the base CRL number 20240720"
+		if err == nil || err.Error() != expectedErrorMsg {
+			t.Fatalf("expected error %q, got %v", expectedErrorMsg, err)
+		}
+	})
+
+	t.Run("delta crl without delta crl indicator", func(t *testing.T) {
+		deltaCRLBytes, err := x509.CreateRevocationList(rand.Reader, &x509.RevocationList{
+			NextUpdate: time.Now().Add(time.Hour),
+			Number:     big.NewInt(20240721),
+		}, issuerCert, issuerKey)
+		if err != nil {
+			t.Fatal(err)
+		}
+		deltaCRL, err := x509.ParseRevocationList(deltaCRLBytes)
+		if err != nil {
+			t.Fatal(err)
+		}
+		bundle := &crlutils.Bundle{
+			BaseCRL:  crl,
+			DeltaCRL: deltaCRL,
+		}
+		err = validate(bundle, issuerCert)
+		expectedErrorMsg := "delta CRL indicator extension is not found"
+		if err == nil || err.Error() != expectedErrorMsg {
+			t.Fatalf("expected error %q, got %v", expectedErrorMsg, err)
+		}
+	})
+
+	t.Run("delta crl minimum base crl number is greater than base crl", func(t *testing.T) {
+		deltaCRLIndicator := big.NewInt(20240721)
+		deltaCRLIndicatorBytes, err := asn1.Marshal(deltaCRLIndicator)
+		if err != nil {
+			t.Fatal(err)
+		}
+		deltaCRLBytes, err := x509.CreateRevocationList(rand.Reader, &x509.RevocationList{
+			NextUpdate: time.Now().Add(time.Hour),
+			Number:     big.NewInt(20240722),
+			ExtraExtensions: []pkix.Extension{
+				{
+					Id:       oidDeltaCRLIndicator,
+					Critical: true,
+					Value:    deltaCRLIndicatorBytes,
+				},
+			},
+		}, issuerCert, issuerKey)
+		if err != nil {
+			t.Fatal(err)
+		}
+		deltaCRL, err := x509.ParseRevocationList(deltaCRLBytes)
+		if err != nil {
+			t.Fatal(err)
+		}
+		bundle := &crlutils.Bundle{
+			BaseCRL:  crl,
+			DeltaCRL: deltaCRL,
+		}
+		err = validate(bundle, issuerCert)
+		expectedErrorMsg := "delta CRL indicator 20240721 is not less than or equal to the base CRL number 20240720"
+		if err == nil || err.Error() != expectedErrorMsg {
+			t.Fatalf("expected error %q, got %v", expectedErrorMsg, err)
+		}
+	})
+
+	t.Run("delta crl with invalid delta indicator extension", func(t *testing.T) {
+		deltaCRLBytes, err := x509.CreateRevocationList(rand.Reader, &x509.RevocationList{
+			NextUpdate: time.Now().Add(time.Hour),
+			Number:     big.NewInt(20240722),
+			ExtraExtensions: []pkix.Extension{
+				{
+					Id:       oidDeltaCRLIndicator,
+					Critical: true,
+					Value:    []byte("invalid"),
+				},
+			},
+		}, issuerCert, issuerKey)
+		if err != nil {
+			t.Fatal(err)
+		}
+		deltaCRL, err := x509.ParseRevocationList(deltaCRLBytes)
+		if err != nil {
+			t.Fatal(err)
+		}
+		bundle := &crlutils.Bundle{
+			BaseCRL:  crl,
+			DeltaCRL: deltaCRL,
+		}
+		err = validate(bundle, issuerCert)
+		expectedErrorMsg := "failed to parse delta CRL indicator extension"
+		if err == nil || err.Error() != expectedErrorMsg {
+			t.Fatalf("expected error %q, got %v", expectedErrorMsg, err)
 		}
 	})
 }
@@ -461,14 +641,22 @@ func TestCheckRevocation(t *testing.T) {
 	signingTime := time.Now()
 
 	t.Run("certificate is nil", func(t *testing.T) {
-		_, err := checkRevocation(nil, &x509.RevocationList{}, signingTime, "")
+		_, err := checkRevocation(nil, &crlutils.Bundle{BaseCRL: &x509.RevocationList{}}, signingTime, "")
 		if err == nil {
 			t.Fatal("expected error")
 		}
 	})
 
-	t.Run("CRL is nil", func(t *testing.T) {
+	t.Run("bundle is nil", func(t *testing.T) {
 		_, err := checkRevocation(cert, nil, signingTime, "")
+		expectedErrorMsg := "CRL bundle cannot be nil"
+		if err == nil || err.Error() != expectedErrorMsg {
+			t.Fatalf("expected error %q, got %v", expectedErrorMsg, err)
+		}
+	})
+
+	t.Run("CRL is nil", func(t *testing.T) {
+		_, err := checkRevocation(cert, &crlutils.Bundle{}, signingTime, "")
 		if err == nil {
 			t.Fatal("expected error")
 		}
@@ -482,7 +670,7 @@ func TestCheckRevocation(t *testing.T) {
 				},
 			},
 		}
-		r, err := checkRevocation(cert, baseCRL, signingTime, "")
+		r, err := checkRevocation(cert, &crlutils.Bundle{BaseCRL: baseCRL}, signingTime, "")
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -500,7 +688,26 @@ func TestCheckRevocation(t *testing.T) {
 				},
 			},
 		}
-		r, err := checkRevocation(cert, baseCRL, signingTime, "")
+		r, err := checkRevocation(cert, &crlutils.Bundle{BaseCRL: baseCRL}, signingTime, "")
+		if err != nil {
+			t.Fatal(err)
+		}
+		if r.Result != result.ResultRevoked {
+			t.Fatalf("expected revoked, got %s", r.Result)
+		}
+	})
+
+	t.Run("revoked in delta CRL", func(t *testing.T) {
+		baseCRL := &x509.RevocationList{}
+		deltaCRL := &x509.RevocationList{
+			RevokedCertificateEntries: []x509.RevocationListEntry{
+				{
+					SerialNumber:   big.NewInt(1),
+					RevocationTime: time.Now().Add(-time.Hour),
+				},
+			},
+		}
+		r, err := checkRevocation(cert, &crlutils.Bundle{BaseCRL: baseCRL, DeltaCRL: deltaCRL}, signingTime, "")
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -533,7 +740,7 @@ func TestCheckRevocation(t *testing.T) {
 				},
 			},
 		}
-		r, err := checkRevocation(cert, baseCRL, signingTime, "")
+		r, err := checkRevocation(cert, &crlutils.Bundle{BaseCRL: baseCRL}, signingTime, "")
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -566,7 +773,7 @@ func TestCheckRevocation(t *testing.T) {
 				},
 			},
 		}
-		r, err := checkRevocation(cert, baseCRL, signingTime, "")
+		r, err := checkRevocation(cert, &crlutils.Bundle{BaseCRL: baseCRL}, signingTime, "")
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -584,7 +791,7 @@ func TestCheckRevocation(t *testing.T) {
 				},
 			},
 		}
-		r, err := checkRevocation(cert, baseCRL, time.Time{}, "")
+		r, err := checkRevocation(cert, &crlutils.Bundle{BaseCRL: baseCRL}, time.Time{}, "")
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -607,16 +814,129 @@ func TestCheckRevocation(t *testing.T) {
 				},
 			},
 		}
-		_, err := checkRevocation(cert, baseCRL, signingTime, "")
+		_, err := checkRevocation(cert, &crlutils.Bundle{BaseCRL: baseCRL}, signingTime, "")
 		if err == nil {
 			t.Fatal("expected error")
 		}
 	})
+
+	t.Run("delta crl with certificate hold", func(t *testing.T) {
+		baseCRL := &x509.RevocationList{}
+		deltaCRL := &x509.RevocationList{
+			RevokedCertificateEntries: []x509.RevocationListEntry{
+				{
+					SerialNumber: big.NewInt(1),
+					ReasonCode:   reasonCodeCertificateHold,
+				},
+			},
+		}
+		r, err := checkRevocation(cert, &crlutils.Bundle{BaseCRL: baseCRL, DeltaCRL: deltaCRL}, signingTime, "")
+		if err != nil {
+			t.Fatal(err)
+		}
+		if r.Result != result.ResultRevoked {
+			t.Fatalf("expected revoked, got %s", r.Result)
+		}
+	})
+
+	t.Run("certificate hold and remove hold", func(t *testing.T) {
+		baseCRL := &x509.RevocationList{
+			RevokedCertificateEntries: []x509.RevocationListEntry{
+				{
+					SerialNumber:   big.NewInt(1),
+					ReasonCode:     reasonCodeCertificateHold,
+					RevocationTime: time.Now().Add(-time.Hour),
+				},
+			},
+		}
+		deltaCRL := &x509.RevocationList{
+			RevokedCertificateEntries: []x509.RevocationListEntry{
+				{
+					SerialNumber:   big.NewInt(1),
+					ReasonCode:     reasonCodeRemoveFromCRL,
+					RevocationTime: time.Now(),
+				},
+			},
+		}
+		r, err := checkRevocation(cert, &crlutils.Bundle{BaseCRL: baseCRL, DeltaCRL: deltaCRL}, signingTime, "")
+		if err != nil {
+			t.Fatal(err)
+		}
+		if r.Result != result.ResultOK {
+			t.Fatalf("expected OK, got %s", r.Result)
+		}
+	})
+
+	t.Run("certificate hold and remove hold with other other certificate hold", func(t *testing.T) {
+		baseCRL := &x509.RevocationList{
+			RevokedCertificateEntries: []x509.RevocationListEntry{
+				{
+					SerialNumber:   big.NewInt(1),
+					ReasonCode:     reasonCodeCertificateHold,
+					RevocationTime: time.Now().Add(-time.Hour),
+				},
+			},
+		}
+		deltaCRL := &x509.RevocationList{
+			RevokedCertificateEntries: []x509.RevocationListEntry{
+				{
+					SerialNumber:   big.NewInt(1),
+					ReasonCode:     reasonCodeRemoveFromCRL,
+					RevocationTime: time.Now(),
+				},
+				{
+					SerialNumber:   big.NewInt(2),
+					ReasonCode:     reasonCodeCertificateHold,
+					RevocationTime: time.Now(),
+				},
+			},
+		}
+		r, err := checkRevocation(cert, &crlutils.Bundle{BaseCRL: baseCRL, DeltaCRL: deltaCRL}, signingTime, "")
+		if err != nil {
+			t.Fatal(err)
+		}
+		if r.Result != result.ResultOK {
+			t.Fatalf("expected OK, got %s", r.Result)
+		}
+	})
+
+	t.Run("certificate hold, remove hold and hold again", func(t *testing.T) {
+		baseCRL := &x509.RevocationList{
+			RevokedCertificateEntries: []x509.RevocationListEntry{
+				{
+					SerialNumber:   big.NewInt(1),
+					ReasonCode:     reasonCodeCertificateHold,
+					RevocationTime: time.Now().Add(-2 * time.Hour),
+				},
+			},
+		}
+		deltaCRL := &x509.RevocationList{
+			RevokedCertificateEntries: []x509.RevocationListEntry{
+				{
+					SerialNumber:   big.NewInt(1),
+					ReasonCode:     reasonCodeRemoveFromCRL,
+					RevocationTime: time.Now().Add(-time.Hour),
+				},
+				{
+					SerialNumber:   big.NewInt(1),
+					ReasonCode:     reasonCodeCertificateHold,
+					RevocationTime: time.Now(),
+				},
+			},
+		}
+		r, err := checkRevocation(cert, &crlutils.Bundle{BaseCRL: baseCRL, DeltaCRL: deltaCRL}, signingTime, "")
+		if err != nil {
+			t.Fatal(err)
+		}
+		if r.Result != result.ResultRevoked {
+			t.Fatalf("expected revoked, got %s", r.Result)
+		}
+	})
 }
 
 func TestParseEntryExtension(t *testing.T) {
 	t.Run("unsupported critical extension", func(t *testing.T) {
-		entry := x509.RevocationListEntry{
+		entry := &x509.RevocationListEntry{
 			Extensions: []pkix.Extension{
 				{
 					Id:       []int{1, 2, 3},
@@ -630,7 +950,7 @@ func TestParseEntryExtension(t *testing.T) {
 	})
 
 	t.Run("valid extension", func(t *testing.T) {
-		entry := x509.RevocationListEntry{
+		entry := &x509.RevocationListEntry{
 			Extensions: []pkix.Extension{
 				{
 					Id:       []int{1, 2, 3},
@@ -652,7 +972,7 @@ func TestParseEntryExtension(t *testing.T) {
 			t.Fatal(err)
 		}
 
-		entry := x509.RevocationListEntry{
+		entry := &x509.RevocationListEntry{
 			Extensions: []pkix.Extension{
 				{
 					Id:       oidInvalidityDate,
@@ -673,7 +993,7 @@ func TestParseEntryExtension(t *testing.T) {
 
 	t.Run("parse invalidityDate with error", func(t *testing.T) {
 		// invalid invalidityDate extension
-		entry := x509.RevocationListEntry{
+		entry := &x509.RevocationListEntry{
 			Extensions: []pkix.Extension{
 				{
 					Id:       oidInvalidityDate,
@@ -695,7 +1015,7 @@ func TestParseEntryExtension(t *testing.T) {
 		}
 		invalidityDateBytes = append(invalidityDateBytes, 0x00)
 
-		entry = x509.RevocationListEntry{
+		entry = &x509.RevocationListEntry{
 			Extensions: []pkix.Extension{
 				{
 					Id:       oidInvalidityDate,

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

@@ -12,7 +12,8 @@
 // limitations under the License.
 
 // Package x509util provides the method to validate the certificate chain for a
-// specific purpose, including code signing and timestamping.
+// specific purpose, including code signing and timestamping. It also provides
+// the method to find the extension by the given OID.
 package x509util
 
 import (

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.

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())

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
-// with one of the trusted certificates and returns a certificate that matches
-// with one of the certificates in the SignerInfo.
+// VerifyAuthenticity iterates the certificate chain in signerInfo, for each
+// certificate in the chain, it checks if the certificate matches with one of
+// 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 _, cert := range signerInfo.CertificateChain {
+		for _, trust := range trustedCerts {
 			if trust.Equal(cert) {
 				return trust, nil
 			}