Add the ability to specify certificate identity via a regular express…

…ion (#236)

For #234

---------

Signed-off-by: Zach Steindler <steiza@github.com>

cmd/conformance/main.go

@@ -284,7 +284,7 @@ func main() {
 
 		identityPolicies := []verify.PolicyOption{}
 		if *certOIDC != "" || *certSAN != "" {
-			certID, err := verify.NewShortCertificateIdentity(*certOIDC, *certSAN, "")
+			certID, err := verify.NewShortCertificateIdentity(*certOIDC, "", *certSAN, "")
 			if err != nil {
 				fmt.Println(err)
 				os.Exit(1)
@@ -333,7 +333,7 @@ func main() {
 		// Configure verification options
 		identityPolicies := []verify.PolicyOption{}
 		if *certOIDC != "" || *certSAN != "" {
-			certID, err := verify.NewShortCertificateIdentity(*certOIDC, *certSAN, "")
+			certID, err := verify.NewShortCertificateIdentity(*certOIDC, "", *certSAN, "")
 			if err != nil {
 				fmt.Println(err)
 				os.Exit(1)

cmd/sigstore-go/main.go

@@ -41,6 +41,7 @@ var artifact *string
 var artifactDigest *string
 var artifactDigestAlgorithm *string
 var expectedOIDIssuer *string
+var expectedOIDIssuerRegex *string
 var expectedSAN *string
 var expectedSANRegex *string
 var requireTimestamp *bool
@@ -58,6 +59,7 @@ func init() {
 	artifactDigest = flag.String("artifact-digest", "", "Hex-encoded digest of artifact to verify")
 	artifactDigestAlgorithm = flag.String("artifact-digest-algorithm", "sha256", "Digest algorithm")
 	expectedOIDIssuer = flag.String("expectedIssuer", "", "The expected OIDC issuer for the signing certificate")
+	expectedOIDIssuerRegex = flag.String("expectedIssuerRegex", "", "The expected OIDC issuer for the signing certificate")
 	expectedSAN = flag.String("expectedSAN", "", "The expected identity in the signing certificate's SAN extension")
 	expectedSANRegex = flag.String("expectedSANRegex", "", "The expected identity in the signing certificate's SAN extension")
 	requireTimestamp = flag.Bool("requireTimestamp", true, "Require either an RFC3161 signed timestamp or log entry integrated timestamp")
@@ -120,7 +122,7 @@ func run() error {
 		verifierConfig = append(verifierConfig, verify.WithOnlineVerification())
 	}
 
-	certID, err := verify.NewShortCertificateIdentity(*expectedOIDIssuer, *expectedSAN, *expectedSANRegex)
+	certID, err := verify.NewShortCertificateIdentity(*expectedOIDIssuer, *expectedOIDIssuerRegex, *expectedSAN, *expectedSANRegex)
 	if err != nil {
 		return err
 	}

docs/verification.md

@@ -95,7 +95,7 @@ Then, we need to prepare the expected artifact digest. Note that this option has
 In this case, we also need to prepare the expected certificate identity. Note that this option has an alternative option `WithoutIdentitiesUnsafe`. This is a failsafe to ensure that the caller is aware that simply verifying the bundle is not enough, you must also verify the contents of the bundle against a specific identity. If your bundle was signed with a key, and thus does not have a certificate identity, a better choice is to use the `WithKey` option.
 
 ```go
-	certID, err := verify.NewShortCertificateIdentity("https://token.actions.githubusercontent.com", "", "^https://github.com/sigstore/sigstore-js/")
+	certID, err := verify.NewShortCertificateIdentity("https://token.actions.githubusercontent.com", "", "", "^https://github.com/sigstore/sigstore-js/")
 	if err != nil {
 		panic(err)
 	}
@@ -221,7 +221,7 @@ func main() {
 		panic(err)
 	}
 
-	certID, err := verify.NewShortCertificateIdentity("https://token.actions.githubusercontent.com", "", "^https://github.com/sigstore/sigstore-js/")
+	certID, err := verify.NewShortCertificateIdentity("https://token.actions.githubusercontent.com", "", "", "^https://github.com/sigstore/sigstore-js/")
 	if err != nil {
 		panic(err)
 	}

examples/oci-image-verification/main.go

@@ -48,6 +48,7 @@ var artifact *string
 var artifactDigest *string
 var artifactDigestAlgorithm *string
 var expectedOIDIssuer *string
+var expectedOIDIssuerRegex *string
 var expectedSAN *string
 var expectedSANRegex *string
 var requireTimestamp *bool
@@ -65,6 +66,7 @@ func init() {
 	artifactDigest = flag.String("artifact-digest", "", "Hex-encoded digest of artifact to verify")
 	artifactDigestAlgorithm = flag.String("artifact-digest-algorithm", "sha256", "Digest algorithm")
 	expectedOIDIssuer = flag.String("expectedIssuer", "", "The expected OIDC issuer for the signing certificate")
+	expectedOIDIssuerRegex = flag.String("expectedIssuerRegex", "", "The expected OIDC issuer for the signing certificate")
 	expectedSAN = flag.String("expectedSAN", "", "The expected identity in the signing certificate's SAN extension")
 	expectedSANRegex = flag.String("expectedSANRegex", "", "The expected identity in the signing certificate's SAN extension")
 	requireTimestamp = flag.Bool("requireTimestamp", true, "Require either an RFC3161 signed timestamp or log entry integrated timestamp")
@@ -133,8 +135,8 @@ func run() error {
 		verifierConfig = append(verifierConfig, verify.WithOnlineVerification())
 	}
 
-	if *expectedOIDIssuer != "" || *expectedSAN != "" || *expectedSANRegex != "" {
-		certID, err := verify.NewShortCertificateIdentity(*expectedOIDIssuer, *expectedSAN, *expectedSANRegex)
+	if *expectedOIDIssuer != "" || *expectedOIDIssuerRegex != "" || *expectedSAN != "" || *expectedSANRegex != "" {
+		certID, err := verify.NewShortCertificateIdentity(*expectedOIDIssuer, *expectedOIDIssuerRegex, *expectedSAN, *expectedSANRegex)
 		if err != nil {
 			return err
 		}

pkg/verify/certificate_identity.go

@@ -28,38 +28,37 @@ type SubjectAlternativeNameMatcher struct {
 	Regexp                 regexp.Regexp `json:"regexp,omitempty"`
 }
 
+type IssuerMatcher struct {
+	Issuer string        `json:"issuer"`
+	Regexp regexp.Regexp `json:"regexp,omitempty"`
+}
+
 type CertificateIdentity struct {
 	SubjectAlternativeName SubjectAlternativeNameMatcher `json:"subjectAlternativeName"`
+	Issuer                 IssuerMatcher                 `json:"issuer"`
 	certificate.Extensions
 }
 
 type CertificateIdentities []CertificateIdentity
 
-type ErrSANTypeMismatch struct {
+type ErrValueMismatch struct {
+	object   string
 	expected string
 	actual   string
 }
 
-func (e *ErrSANTypeMismatch) Error() string {
-	return fmt.Sprintf("expected SAN type %s, got %s", e.expected, e.actual)
+func (e *ErrValueMismatch) Error() string {
+	return fmt.Sprintf("expected %s value \"%s\", got \"%s\"", e.object, e.expected, e.actual)
 }
 
-type ErrSANValueMismatch struct {
-	expected string
-	actual   string
+type ErrValueRegexMismatch struct {
+	object string
+	regex  string
+	value  string
 }
 
-func (e *ErrSANValueMismatch) Error() string {
-	return fmt.Sprintf("expected SAN value \"%s\", got \"%s\"", e.expected, e.actual)
-}
-
-type ErrSANValueRegexMismatch struct {
-	regex string
-	value string
-}
-
-func (e *ErrSANValueRegexMismatch) Error() string {
-	return fmt.Sprintf("expected SAN value to match regex \"%s\", got \"%s\"", e.regex, e.value)
+func (e *ErrValueRegexMismatch) Error() string {
+	return fmt.Sprintf("expected %s value to match regex \"%s\", got \"%s\"", e.object, e.regex, e.value)
 }
 
 type ErrNoMatchingCertificateIdentity struct {
@@ -106,25 +105,65 @@ func (s *SubjectAlternativeNameMatcher) MarshalJSON() ([]byte, error) {
 func (s SubjectAlternativeNameMatcher) Verify(actualCert certificate.Summary) error {
 	if s.SubjectAlternativeName != "" &&
 		actualCert.SubjectAlternativeName != s.SubjectAlternativeName {
-		return &ErrSANValueMismatch{string(s.SubjectAlternativeName), string(actualCert.SubjectAlternativeName)}
+		return &ErrValueMismatch{"SAN", string(s.SubjectAlternativeName), string(actualCert.SubjectAlternativeName)}
 	}
 
 	if s.Regexp.String() != "" &&
 		!s.Regexp.MatchString(actualCert.SubjectAlternativeName) {
-		return &ErrSANValueRegexMismatch{string(s.Regexp.String()), string(actualCert.SubjectAlternativeName)}
+		return &ErrValueRegexMismatch{"SAN", string(s.Regexp.String()), string(actualCert.SubjectAlternativeName)}
+	}
+	return nil
+}
+
+func NewIssuserMatcher(issuerValue, regexpStr string) (IssuerMatcher, error) {
+	r, err := regexp.Compile(regexpStr)
+	if err != nil {
+		return IssuerMatcher{}, err
+	}
+
+	return IssuerMatcher{Issuer: issuerValue, Regexp: *r}, nil
+}
+
+func (i *IssuerMatcher) MarshalJSON() ([]byte, error) {
+	return json.Marshal(&struct {
+		Issuer string `json:"issuer"`
+		Regexp string `json:"regexp,omitempty"`
+	}{
+		Issuer: i.Issuer,
+		Regexp: i.Regexp.String(),
+	})
+}
+
+func (i IssuerMatcher) Verify(actualCert certificate.Summary) error {
+	if i.Issuer != "" &&
+		actualCert.Extensions.Issuer != i.Issuer {
+		return &ErrValueMismatch{"issuer", string(i.Issuer), string(actualCert.Extensions.Issuer)}
+	}
+
+	if i.Regexp.String() != "" &&
+		!i.Regexp.MatchString(actualCert.Extensions.Issuer) {
+		return &ErrValueRegexMismatch{"issuer", string(i.Regexp.String()), string(actualCert.Extensions.Issuer)}
 	}
 	return nil
 }
 
-func NewCertificateIdentity(sanMatcher SubjectAlternativeNameMatcher, extensions certificate.Extensions) (CertificateIdentity, error) {
+func NewCertificateIdentity(sanMatcher SubjectAlternativeNameMatcher, issuerMatcher IssuerMatcher, extensions certificate.Extensions) (CertificateIdentity, error) {
 	if sanMatcher.SubjectAlternativeName == "" && sanMatcher.Regexp.String() == "" {
 		return CertificateIdentity{}, errors.New("when verifying a certificate identity, there must be subject alternative name criteria")
 	}
 
-	certID := CertificateIdentity{SubjectAlternativeName: sanMatcher, Extensions: extensions}
+	if issuerMatcher.Issuer == "" && issuerMatcher.Regexp.String() == "" {
+		return CertificateIdentity{}, errors.New("when verifying a certificate identity, must specify Issuer criteria")
+	}
+
+	if extensions.Issuer != "" {
+		return CertificateIdentity{}, errors.New("please specify issuer in IssuerMatcher, not Extensions")
+	}
 
-	if certID.Issuer == "" {
-		return CertificateIdentity{}, errors.New("when verifying a certificate identity, the Issuer field can't be empty")
+	certID := CertificateIdentity{
+		SubjectAlternativeName: sanMatcher,
+		Issuer:                 issuerMatcher,
+		Extensions:             extensions,
 	}
 
 	return certID, nil
@@ -133,13 +172,18 @@ func NewCertificateIdentity(sanMatcher SubjectAlternativeNameMatcher, extensions
 // NewShortCertificateIdentity provides a more convenient way of initializing
 // a CertificiateIdentity with a SAN and the Issuer OID extension. If you need
 // to check more OID extensions, use NewCertificateIdentity instead.
-func NewShortCertificateIdentity(issuer, sanValue, sanRegex string) (CertificateIdentity, error) {
+func NewShortCertificateIdentity(issuer, issuerRegex, sanValue, sanRegex string) (CertificateIdentity, error) {
 	sanMatcher, err := NewSANMatcher(sanValue, sanRegex)
 	if err != nil {
 		return CertificateIdentity{}, err
 	}
 
-	return NewCertificateIdentity(sanMatcher, certificate.Extensions{Issuer: issuer})
+	issuerMatcher, err := NewIssuserMatcher(issuer, issuerRegex)
+	if err != nil {
+		return CertificateIdentity{}, err
+	}
+
+	return NewCertificateIdentity(sanMatcher, issuerMatcher, certificate.Extensions{})
 }
 
 // Verify verifies the CertificateIdentities, and if ANY of them match the cert,
@@ -164,5 +208,10 @@ func (c CertificateIdentity) Verify(actualCert certificate.Summary) error {
 	if err = c.SubjectAlternativeName.Verify(actualCert); err != nil {
 		return err
 	}
+
+	if err = c.Issuer.Verify(actualCert); err != nil {
+		return err
+	}
+
 	return certificate.CompareExtensions(c.Extensions, actualCert.Extensions)
 }

pkg/verify/certificate_identity_test.go

@@ -23,6 +23,7 @@ import (
 
 const (
 	ActionsIssuerValue = "https://token.actions.githubusercontent.com"
+	ActionsIssuerRegex = "githubusercontent.com$"
 	SigstoreSanValue   = "https://github.com/sigstore/sigstore-js/.github/workflows/release.yml@refs/heads/main"
 	SigstoreSanRegex   = "^https://github.com/sigstore/sigstore-js/"
 )
@@ -57,31 +58,38 @@ func TestCertificateIdentityVerify(t *testing.T) {
 	}
 
 	// First, let's test happy paths:
-	issuerOnlyID, _ := certIDForTesting("", "", ActionsIssuerValue, "")
+	issuerOnlyID, _ := certIDForTesting("", "", ActionsIssuerValue, "", "")
 	assert.NoError(t, issuerOnlyID.Verify(actualCert))
 
-	sanValueOnly, _ := certIDForTesting(SigstoreSanValue, "", "", "")
+	issuerOnlyRegex, _ := certIDForTesting("", "", "", ActionsIssuerRegex, "")
+	assert.NoError(t, issuerOnlyRegex.Verify(actualCert))
+
+	sanValueOnly, _ := certIDForTesting(SigstoreSanValue, "", "", "", "")
 	assert.NoError(t, sanValueOnly.Verify(actualCert))
 
-	sanRegexOnly, _ := certIDForTesting("", SigstoreSanRegex, "", "")
+	sanRegexOnly, _ := certIDForTesting("", SigstoreSanRegex, "", "", "")
 	assert.NoError(t, sanRegexOnly.Verify(actualCert))
 
 	// multiple values can be specified
-	sanRegexAndIssuer, _ := certIDForTesting("", SigstoreSanRegex, ActionsIssuerValue, "github-hosted")
+	sanRegexAndIssuer, _ := certIDForTesting("", SigstoreSanRegex, ActionsIssuerValue, "", "github-hosted")
 	assert.NoError(t, sanRegexAndIssuer.Verify(actualCert))
 
 	// unhappy paths:
 	// wrong issuer
-	sanRegexAndWrongIssuer, _ := certIDForTesting("", SigstoreSanRegex, "https://token.actions.example.com", "")
-	errCompareExtensions := &certificate.ErrCompareExtensions{}
-	assert.ErrorAs(t, sanRegexAndWrongIssuer.Verify(actualCert), &errCompareExtensions)
-	assert.Equal(t, "expected Issuer to be \"https://token.actions.example.com\", got \"https://token.actions.githubusercontent.com\"", errCompareExtensions.Error())
+	sanRegexAndWrongIssuer, _ := certIDForTesting("", SigstoreSanRegex, "https://token.actions.example.com", "", "")
+	errValueMismatch := &ErrValueMismatch{}
+	assert.ErrorAs(t, sanRegexAndWrongIssuer.Verify(actualCert), &errValueMismatch)
+	assert.Equal(t, "expected issuer value \"https://token.actions.example.com\", got \"https://token.actions.githubusercontent.com\"", errValueMismatch.Error())
 
 	// bad san regex
-	badRegex, _ := certIDForTesting("", "^badregex.*", "", "")
-	errSANValueRegexMismatch := &ErrSANValueRegexMismatch{}
-	assert.ErrorAs(t, badRegex.Verify(actualCert), &errSANValueRegexMismatch)
-	assert.Equal(t, "expected SAN value to match regex \"^badregex.*\", got \"https://github.com/sigstore/sigstore-js/.github/workflows/release.yml@refs/heads/main\"", errSANValueRegexMismatch.Error())
+	badRegex, _ := certIDForTesting("", "^badregex.*", "", "", "")
+	errValueRegexMismatch := &ErrValueRegexMismatch{}
+	assert.ErrorAs(t, badRegex.Verify(actualCert), &errValueRegexMismatch)
+	assert.Equal(t, "expected SAN value to match regex \"^badregex.*\", got \"https://github.com/sigstore/sigstore-js/.github/workflows/release.yml@refs/heads/main\"", errValueRegexMismatch.Error())
+
+	// bad issuer regex
+	badIssuerRegex, _ := certIDForTesting("", "", "", "^badregex$", "")
+	assert.Error(t, badIssuerRegex.Verify(actualCert))
 
 	// if we have an array of certIDs, only one needs to match
 	ci, err := CertificateIdentities{sanRegexAndWrongIssuer, sanRegexAndIssuer}.Verify(actualCert)
@@ -91,12 +99,12 @@ func TestCertificateIdentityVerify(t *testing.T) {
 	// if none match, we fail
 	ci, err = CertificateIdentities{badRegex, sanRegexAndWrongIssuer}.Verify(actualCert)
 	assert.Error(t, err)
-	assert.Equal(t, "no matching CertificateIdentity found, last error: expected Issuer to be \"https://token.actions.example.com\", got \"https://token.actions.githubusercontent.com\"", err.Error())
+	assert.Equal(t, "no matching CertificateIdentity found, last error: expected issuer value \"https://token.actions.example.com\", got \"https://token.actions.githubusercontent.com\"", err.Error())
 	assert.Nil(t, ci)
 	// test err unwrap for previous error
-	errCompareExtensions = &certificate.ErrCompareExtensions{}
-	assert.ErrorAs(t, err, &errCompareExtensions)
-	assert.Equal(t, "expected Issuer to be \"https://token.actions.example.com\", got \"https://token.actions.githubusercontent.com\"", errCompareExtensions.Error())
+	errValueMismatch = &ErrValueMismatch{}
+	assert.ErrorAs(t, err, &errValueMismatch)
+	assert.Equal(t, "expected issuer value \"https://token.actions.example.com\", got \"https://token.actions.githubusercontent.com\"", errValueMismatch.Error())
 
 	// if no certIDs are specified, we fail
 	_, err = CertificateIdentities{}.Verify(actualCert)
@@ -105,24 +113,35 @@ func TestCertificateIdentityVerify(t *testing.T) {
 }
 
 func TestThatCertIDsAreFullySpecified(t *testing.T) {
-	_, err := NewShortCertificateIdentity("", "", "")
+	_, err := NewShortCertificateIdentity("", "", "", "")
 	assert.Error(t, err)
 
-	_, err = NewShortCertificateIdentity("foobar", "", "")
+	_, err = NewShortCertificateIdentity("foobar", "", "", "")
 	assert.Error(t, err)
 
-	_, err = NewShortCertificateIdentity("", "", SigstoreSanRegex)
+	_, err = NewShortCertificateIdentity("", ActionsIssuerRegex, "", "")
 	assert.Error(t, err)
 
-	_, err = NewShortCertificateIdentity("foobar", "", SigstoreSanRegex)
+	_, err = NewShortCertificateIdentity("", "", "", SigstoreSanRegex)
+	assert.Error(t, err)
+
+	_, err = NewShortCertificateIdentity("foobar", "", "", SigstoreSanRegex)
+	assert.Nil(t, err)
+
+	_, err = NewShortCertificateIdentity("", ActionsIssuerRegex, "", SigstoreSanRegex)
 	assert.Nil(t, err)
 }
 
-func certIDForTesting(sanValue, sanRegex, issuer, runnerEnv string) (CertificateIdentity, error) {
+func certIDForTesting(sanValue, sanRegex, issuer, issuerRegex, runnerEnv string) (CertificateIdentity, error) {
 	san, err := NewSANMatcher(sanValue, sanRegex)
 	if err != nil {
 		return CertificateIdentity{}, err
 	}
 
-	return CertificateIdentity{SubjectAlternativeName: san, Extensions: certificate.Extensions{Issuer: issuer, RunnerEnvironment: runnerEnv}}, nil
+	issuerMatcher, err := NewIssuserMatcher(issuer, issuerRegex)
+	if err != nil {
+		return CertificateIdentity{}, err
+	}
+
+	return CertificateIdentity{SubjectAlternativeName: san, Issuer: issuerMatcher, Extensions: certificate.Extensions{RunnerEnvironment: runnerEnv}}, nil
 }