Pad the ECDSA key that gets put into the Yubikey so it has 32 bytes.

Apparently that is required by the template, and will error if it
does not. Sometimes, ECDSA keys are generated which when encoded
seems to only have 31 bytes.

Signed-off-by: Ying Li <ying.li@docker.com>
Signed-off-by: David Lawrence <david.lawrence@docker.com>

Signed-off-by: Ying Li <ying.li@docker.com> (github: endophage)

trustmanager/yubikeystore.go

@@ -30,6 +30,9 @@ const (
 	KeymodeTouch     = 1 // touch enabled
 	KeymodePinOnce   = 2 // require pin entry once
 	KeymodePinAlways = 4 // require pin entry all the time
+
+	// the key size, when importing a key into yubikey, MUST be 32 bytes
+	ecdsaPrivateKeySize = 32
 )
 
 // what key mode to use when generating keys
@@ -136,6 +139,18 @@ func (y *YubiPrivateKey) Sign(rand io.Reader, msg []byte, opts crypto.SignerOpts
 	return sig, nil
 }
 
+// If a byte array is less than the number of bytes specified by
+// ecdsaPrivateKeySize, left-zero-pad the byte array until
+// it is the required size.
+func ensurePrivateKeySize(payload []byte) []byte {
+	final := payload
+	if len(payload) < ecdsaPrivateKeySize {
+		final = make([]byte, ecdsaPrivateKeySize)
+		copy(final[ecdsaPrivateKeySize-len(payload):], payload)
+	}
+	return final
+}
+
 // addECDSAKey adds a key to the yubikey
 func addECDSAKey(
 	ctx *pkcs11.Ctx,
@@ -161,7 +176,7 @@ func addECDSAKey(
 		return err
 	}
 
-	ecdsaPrivKeyD := ecdsaPrivKey.D.Bytes()
+	ecdsaPrivKeyD := ensurePrivateKeySize(ecdsaPrivKey.D.Bytes())
 	logrus.Debugf("Getting D bytes: %v\n", ecdsaPrivKeyD)
 
 	template, err := NewCertificate(role)

trustmanager/yubikeystore_test.go

@@ -4,6 +4,7 @@ package trustmanager
 
 import (
 	"crypto/rand"
+	"reflect"
 	"testing"
 
 	"github.com/docker/notary/passphrase"
@@ -25,6 +26,32 @@ func clearAllKeys(t *testing.T) {
 	}
 }
 
+func TestEnsurePrivateKeySizePassesThroughRightSizeArrays(t *testing.T) {
+	fullByteArray := make([]byte, ecdsaPrivateKeySize)
+	for i := range fullByteArray {
+		fullByteArray[i] = byte(1)
+	}
+
+	result := ensurePrivateKeySize(fullByteArray)
+	assert.True(t, reflect.DeepEqual(fullByteArray, result))
+}
+
+// The pad32Byte helper function left zero-pads byte arrays that are less than
+// ecdsaPrivateKeySize bytes
+func TestEnsurePrivateKeySizePadsLessThanRequiredSizeArrays(t *testing.T) {
+	shortByteArray := make([]byte, ecdsaPrivateKeySize/2)
+	for i := range shortByteArray {
+		shortByteArray[i] = byte(1)
+	}
+
+	expected := append(
+		make([]byte, ecdsaPrivateKeySize-ecdsaPrivateKeySize/2),
+		shortByteArray...)
+
+	result := ensurePrivateKeySize(shortByteArray)
+	assert.True(t, reflect.DeepEqual(expected, result))
+}
+
 func testAddKey(t *testing.T, store *YubiKeyStore) (data.PrivateKey, error) {
 	privKey, err := GenerateECDSAKey(rand.Reader)
 	assert.NoError(t, err)