Add support for certificate chain to verify certificate

This adds a flag to provide a chain of CA certificates to verify a certificate provided by flag. Callers should include a chain from the parent of the certificate to the root. While it'd be ideal to force the root to be specified out of band, by TUF, that code is currently intertwined with expectations around Fulcio and Rekor usage. Signed-off-by: Hayden Blauzvern <hblauzvern@google.com>
sigstore · Mar 25, 2022 · 0dd4508 · 0dd4508
1 parent 7402eb4
commit 0dd4508
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Showing 13 changed files with 98 additions and 6 deletions.
diff --git a/cmd/cosign/cli/dockerfile.go b/cmd/cosign/cli/dockerfile.go
@@ -91,6 +91,7 @@ Shell-like variables in the Dockerfile's FROM lines will be substituted with val
 					CertRef:         o.CertVerify.Cert,
 					CertEmail:       o.CertVerify.CertEmail,
 					CertOidcIssuer:  o.CertVerify.CertOidcIssuer,
+					CertChain:       o.CertVerify.CertChain,
 					Sk:              o.SecurityKey.Use,
 					Slot:            o.SecurityKey.Slot,
 					Output:          o.Output,

diff --git a/cmd/cosign/cli/manifest.go b/cmd/cosign/cli/manifest.go
@@ -86,6 +86,7 @@ against the transparency log.`,
 					CertRef:         o.CertVerify.Cert,
 					CertEmail:       o.CertVerify.CertEmail,
 					CertOidcIssuer:  o.CertVerify.CertOidcIssuer,
+					CertChain:       o.CertVerify.CertChain,
 					Sk:              o.SecurityKey.Use,
 					Slot:            o.SecurityKey.Slot,
 					Output:          o.Output,

diff --git a/cmd/cosign/cli/options/certificate.go b/cmd/cosign/cli/options/certificate.go
@@ -23,6 +23,7 @@ type CertVerifyOptions struct {
 	Cert           string
 	CertEmail      string
 	CertOidcIssuer string
+	CertChain      string
 }
 
 var _ Interface = (*RekorOptions)(nil)
@@ -37,4 +38,10 @@ func (o *CertVerifyOptions) AddFlags(cmd *cobra.Command) {
 
 	cmd.Flags().StringVar(&o.CertOidcIssuer, "cert-oidc-issuer", "",
 		"the OIDC issuer expected in a valid Fulcio certificate, e.g. https://token.actions.githubusercontent.com or https://oauth2.sigstore.dev/auth")
+
+	cmd.Flags().StringVar(&o.CertChain, "cert-chain", "",
+		"path to a list of CA certificates in PEM format which will be needed "+
+			"when building the certificate chain for the signing certificate. "+
+			"Must start with the parent intermediate CA certificate of the "+
+			"signing certificate and end with the root certificate")
 }
diff --git a/cmd/cosign/cli/verify.go b/cmd/cosign/cli/verify.go
@@ -56,6 +56,9 @@ against the transparency log.`,
   # verify image with an on-disk signed image from 'cosign save'
   cosign verify --key cosign.pub --local-image <PATH>
 
+  # verify image with local certificate and certificate chain
+  cosign verify --cert cosign.crt --cert-chain chain.crt <IMAGE>
+
   # verify image with public key provided by URL
   cosign verify --key https://host.for/[FILE] <IMAGE>
 
@@ -93,6 +96,7 @@ against the transparency log.`,
 				CertRef:         o.CertVerify.Cert,
 				CertEmail:       o.CertVerify.CertEmail,
 				CertOidcIssuer:  o.CertVerify.CertOidcIssuer,
+				CertChain:       o.CertVerify.CertChain,
 				Sk:              o.SecurityKey.Use,
 				Slot:            o.SecurityKey.Slot,
 				Output:          o.Output,
@@ -169,6 +173,7 @@ against the transparency log.`,
 				CertRef:         o.CertVerify.Cert,
 				CertEmail:       o.CertVerify.CertEmail,
 				CertOidcIssuer:  o.CertVerify.CertOidcIssuer,
+				CertChain:       o.CertVerify.CertChain,
 				KeyRef:          o.Key,
 				Sk:              o.SecurityKey.Use,
 				Slot:            o.SecurityKey.Slot,
@@ -247,7 +252,7 @@ The blob may be specified as a path to a file or - for stdin.`,
 				BundlePath: o.BundlePath,
 			}
 			if err := verify.VerifyBlobCmd(cmd.Context(), ko, o.CertVerify.Cert,
-				o.CertVerify.CertEmail, o.CertVerify.CertOidcIssuer, o.Signature, args[0]); err != nil {
+				o.CertVerify.CertEmail, o.CertVerify.CertOidcIssuer, o.CertVerify.CertChain, o.Signature, args[0]); err != nil {
 				return errors.Wrapf(err, "verifying blob %s", args)
 			}
 			return nil

diff --git a/cmd/cosign/cli/verify/verify.go b/cmd/cosign/cli/verify/verify.go
@@ -16,6 +16,7 @@
 package verify
 
 import (
+	"bytes"
 	"context"
 	"crypto"
 	"crypto/ecdsa"
@@ -53,6 +54,7 @@ type VerifyCommand struct {
 	CertRef        string
 	CertEmail      string
 	CertOidcIssuer string
+	CertChain      string
 	Sk             bool
 	Slot           string
 	Output         string
@@ -139,6 +141,24 @@ func (c *VerifyCommand) Exec(ctx context.Context, images []string) (err error) {
 		if err != nil {
 			return err
 		}
+		// Verify certificate with chain
+		// First intermediate at chain[0], root at chain[n-1]
+		if c.CertChain != "" {
+			certs, err := loadCertChainFromFileOrURL(c.CertChain)
+			if err != nil {
+				return err
+			}
+			rootPool := x509.NewCertPool()
+			rootPool.AddCert(certs[len(certs)-1])
+			subPool := x509.NewCertPool()
+			for _, c := range certs[:len(certs)-1] {
+				subPool.AddCert(c)
+			}
+			err = cosign.TrustedCert(cert, rootPool, subPool)
+			if err != nil {
+				return err
+			}
+		}
 		pubKey, err = signature.LoadECDSAVerifier(cert.PublicKey.(*ecdsa.PublicKey), crypto.SHA256)
 		if err != nil {
 			return err
@@ -296,3 +316,15 @@ func loadCertFromPEM(pems []byte) (*x509.Certificate, error) {
 	}
 	return certs[0], nil
 }
+
+func loadCertChainFromFileOrURL(path string) ([]*x509.Certificate, error) {
+	pems, err := blob.LoadFileOrURL(path)
+	if err != nil {
+		return nil, err
+	}
+	certs, err := cryptoutils.LoadCertificatesFromPEM(bytes.NewReader(pems))
+	if err != nil {
+		return nil, err
+	}
+	return certs, nil
+}
diff --git a/cmd/cosign/cli/verify/verify_attestation.go b/cmd/cosign/cli/verify/verify_attestation.go
@@ -19,6 +19,7 @@ import (
 	"context"
 	"crypto"
 	"crypto/ecdsa"
+	"crypto/x509"
 	"encoding/base64"
 	"encoding/json"
 	"flag"
@@ -51,6 +52,7 @@ type VerifyAttestationCommand struct {
 	CertRef        string
 	CertEmail      string
 	CertOidcIssuer string
+	CertChain      string
 	KeyRef         string
 	Sk             bool
 	Slot           string
@@ -121,6 +123,24 @@ func (c *VerifyAttestationCommand) Exec(ctx context.Context, images []string) (e
 		if err != nil {
 			return errors.Wrap(err, "loading certificate from reference")
 		}
+		// Verify certificate with chain
+		// First intermediate at chain[0], root at chain[n-1]
+		if c.CertChain != "" {
+			certs, err := loadCertChainFromFileOrURL(c.CertChain)
+			if err != nil {
+				return err
+			}
+			rootPool := x509.NewCertPool()
+			rootPool.AddCert(certs[len(certs)-1])
+			subPool := x509.NewCertPool()
+			for _, c := range certs[:len(certs)-1] {
+				subPool.AddCert(c)
+			}
+			err = cosign.TrustedCert(cert, rootPool, subPool)
+			if err != nil {
+				return err
+			}
+		}
 		co.SigVerifier, err = signature.LoadECDSAVerifier(cert.PublicKey.(*ecdsa.PublicKey), crypto.SHA256)
 		if err != nil {
 			return errors.Wrap(err, "creating certificate verifier")

diff --git a/cmd/cosign/cli/verify/verify_blob.go b/cmd/cosign/cli/verify/verify_blob.go
@@ -60,7 +60,7 @@ func isb64(data []byte) bool {
 }
 
 // nolint
-func VerifyBlobCmd(ctx context.Context, ko sign.KeyOpts, certRef, certEmail, certOidcIssuer, sigRef, blobRef string) error {
+func VerifyBlobCmd(ctx context.Context, ko sign.KeyOpts, certRef, certEmail, certOidcIssuer, certChain, sigRef, blobRef string) error {
 	var verifier signature.Verifier
 	var cert *x509.Certificate
 
@@ -104,6 +104,24 @@ func VerifyBlobCmd(ctx context.Context, ko sign.KeyOpts, certRef, certEmail, cer
 		if err != nil {
 			return err
 		}
+		// Verify certificate with chain
+		// First intermediate at chain[0], root at chain[n-1]
+		if certChain != "" {
+			certs, err := loadCertChainFromFileOrURL(certChain)
+			if err != nil {
+				return err
+			}
+			rootPool := x509.NewCertPool()
+			rootPool.AddCert(certs[len(certs)-1])
+			subPool := x509.NewCertPool()
+			for _, c := range certs[:len(certs)-1] {
+				subPool.AddCert(c)
+			}
+			err = cosign.TrustedCert(cert, rootPool, subPool)
+			if err != nil {
+				return err
+			}
+		}
 		verifier, err = signature.LoadECDSAVerifier(cert.PublicKey.(*ecdsa.PublicKey), crypto.SHA256)
 		if err != nil {
 			return err

diff --git a/doc/cosign_dockerfile_verify.md b/doc/cosign_dockerfile_verify.md
diff --git a/doc/cosign_manifest_verify.md b/doc/cosign_manifest_verify.md
diff --git a/doc/cosign_verify-attestation.md b/doc/cosign_verify-attestation.md
diff --git a/doc/cosign_verify-blob.md b/doc/cosign_verify-blob.md
diff --git a/doc/cosign_verify.md b/doc/cosign_verify.md
diff --git a/test/e2e_test.go b/test/e2e_test.go
@@ -501,8 +501,8 @@ func TestSignBlob(t *testing.T) {
 		KeyRef: pubKeyPath2,
 	}
 	// Verify should fail on a bad input
-	mustErr(cliverify.VerifyBlobCmd(ctx, ko1, "" /*certRef*/, "" /*certEmail*/, "" /*certOidcIssuer*/, "badsig", blob), t)
-	mustErr(cliverify.VerifyBlobCmd(ctx, ko2, "" /*certRef*/, "" /*certEmail*/, "" /*certOidcIssuer*/, "badsig", blob), t)
+	mustErr(cliverify.VerifyBlobCmd(ctx, ko1, "" /*certRef*/, "" /*certEmail*/, "" /*certOidcIssuer*/, "" /*certChain*/, "badsig", blob), t)
+	mustErr(cliverify.VerifyBlobCmd(ctx, ko2, "" /*certRef*/, "" /*certEmail*/, "" /*certOidcIssuer*/, "" /*certChain*/, "badsig", blob), t)
 
 	// Now sign the blob with one key
 	ko := sign.KeyOpts{
@@ -514,8 +514,8 @@ func TestSignBlob(t *testing.T) {
 		t.Fatal(err)
 	}
 	// Now verify should work with that one, but not the other
-	must(cliverify.VerifyBlobCmd(ctx, ko1, "" /*certRef*/, "" /*certEmail*/, "" /*certOidcIssuer*/, string(sig), bp), t)
-	mustErr(cliverify.VerifyBlobCmd(ctx, ko2, "" /*certRef*/, "" /*certEmail*/, "" /*certOidcIssuer*/, string(sig), bp), t)
+	must(cliverify.VerifyBlobCmd(ctx, ko1, "" /*certRef*/, "" /*certEmail*/, "" /*certOidcIssuer*/, "" /*certChain*/, string(sig), bp), t)
+	mustErr(cliverify.VerifyBlobCmd(ctx, ko2, "" /*certRef*/, "" /*certEmail*/, "" /*certOidcIssuer*/, "" /*certChain*/, string(sig), bp), t)
 }
 
 func TestSignBlobBundle(t *testing.T) {