add --ca-roots and --ca-intermediates flags to 'cosign verify'

cmd/cosign/cli/options/certificate.go

@@ -33,6 +33,8 @@ type CertVerifyOptions struct {
 	CertGithubWorkflowName       string
 	CertGithubWorkflowRepository string
 	CertGithubWorkflowRef        string
+	CAIntermediates              string
+	CARoots                      string
 	CertChain                    string
 	SCT                          string
 	IgnoreSCT                    bool
@@ -75,12 +77,25 @@ func (o *CertVerifyOptions) AddFlags(cmd *cobra.Command) {
 	cmd.Flags().StringVar(&o.CertGithubWorkflowRef, "certificate-github-workflow-ref", "",
 		"contains the ref claim from the GitHub OIDC Identity token that contains the git ref that the workflow run was based upon.")
 	// -- Cert extensions end --
+	cmd.Flags().StringVar(&o.CAIntermediates, "ca-intermediates", "",
+		"path to a file of intermediate CA certificates in PEM format which will be needed "+
+			"when building the certificate chains for the signing certificate. "+
+			"The flag is optional and must be used together with --ca-roots, conflicts with "+
+			"--certificate-chain.")
+	_ = cmd.Flags().SetAnnotation("ca-intermediates", cobra.BashCompFilenameExt, []string{"cert"})
+	cmd.Flags().StringVar(&o.CARoots, "ca-roots", "",
+		"path to a bundle file of CA certificates in PEM format which will be needed "+
+			"when building the certificate chains for the signing certificate. Conflicts with --certificate-chain.")
+	_ = cmd.Flags().SetAnnotation("ca-roots", cobra.BashCompFilenameExt, []string{"cert"})
+
 	cmd.Flags().StringVar(&o.CertChain, "certificate-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")
+			"signing certificate and end with the root certificate. Conflicts with --ca-roots and --ca-intermediates.")
 	_ = cmd.Flags().SetAnnotation("certificate-chain", cobra.BashCompFilenameExt, []string{"cert"})
+	cmd.MarkFlagsMutuallyExclusive("ca-roots", "certificate-chain")
+	cmd.MarkFlagsMutuallyExclusive("ca-intermediates", "certificate-chain")
 
 	cmd.Flags().StringVar(&o.SCT, "sct", "",
 		"path to a detached Signed Certificate Timestamp, formatted as a RFC6962 AddChainResponse struct. "+

cmd/cosign/cli/verify.go

@@ -62,6 +62,10 @@ against the transparency log.`,
   # verify image with local certificate and certificate chain
   cosign verify --cert cosign.crt --cert-chain chain.crt <IMAGE>
 
+  # verify image with local certificate and certificate bundles of CA roots
+  # and (optionally) CA intermediates
+  cosign verify --cert cosign.crt --ca-roots ca-roots.pem --ca-intermediates ca-intermediates.pem <IMAGE>
+
   # verify image using keyless verification with the given certificate
   # chain and identity parameters, without Fulcio roots (for BYO PKI):
   cosign verify --cert-chain chain.crt --certificate-oidc-issuer https://issuer.example.com --certificate-identity [email protected] <IMAGE>
@@ -115,6 +119,8 @@ against the transparency log.`,
 				CertGithubWorkflowName:       o.CertVerify.CertGithubWorkflowName,
 				CertGithubWorkflowRepository: o.CertVerify.CertGithubWorkflowRepository,
 				CertGithubWorkflowRef:        o.CertVerify.CertGithubWorkflowRef,
+				CAIntermediates:              o.CertVerify.CAIntermediates,
+				CARoots:                      o.CertVerify.CARoots,
 				CertChain:                    o.CertVerify.CertChain,
 				IgnoreSCT:                    o.CertVerify.IgnoreSCT,
 				SCTRef:                       o.CertVerify.SCT,

cmd/cosign/cli/verify/verify.go

@@ -59,6 +59,8 @@ type VerifyCommand struct {
 	CertGithubWorkflowName       string
 	CertGithubWorkflowRepository string
 	CertGithubWorkflowRef        string
+	CAIntermediates              string
+	CARoots                      string
 	CertChain                    string
 	CertOidcProvider             string
 	IgnoreSCT                    bool
@@ -173,7 +175,8 @@ func (c *VerifyCommand) Exec(ctx context.Context, images []string) (err error) {
 		}
 	}
 	if keylessVerification(c.KeyRef, c.Sk) {
-		if c.CertChain != "" {
+		switch {
+		case c.CertChain != "":
 			chain, err := loadCertChainFromFileOrURL(c.CertChain)
 			if err != nil {
 				return err
@@ -186,9 +189,32 @@ func (c *VerifyCommand) Exec(ctx context.Context, images []string) (err error) {
 					co.IntermediateCerts.AddCert(cert)
 				}
 			}
-		} else {
-			// This performs an online fetch of the Fulcio roots. This is needed
-			// for verifying keyless certificates (both online and offline).
+		case c.CARoots != "":
+			caRoots, err := loadCertChainFromFileOrURL(c.CARoots)
+			if err != nil {
+				return err
+			}
+			co.RootCerts = x509.NewCertPool()
+			if len(caRoots) > 0 {
+				for _, cert := range caRoots {
+					co.RootCerts.AddCert(cert)
+				}
+			}
+			if c.CAIntermediates != "" {
+				caIntermediates, err := loadCertChainFromFileOrURL(c.CAIntermediates)
+				if err != nil {
+					return err
+				}
+				if len(caIntermediates) > 0 {
+					co.IntermediateCerts = x509.NewCertPool()
+					for _, cert := range caIntermediates {
+						co.IntermediateCerts.AddCert(cert)
+					}
+				}
+			}
+		default:
+			// This performs an online fetch of the Fulcio roots from a TUF repository.
+			// This is needed for verifying keyless certificates (both online and offline).
 			co.RootCerts, err = fulcio.GetRoots()
 			if err != nil {
 				return fmt.Errorf("getting Fulcio roots: %w", err)
@@ -237,8 +263,9 @@ func (c *VerifyCommand) Exec(ctx context.Context, images []string) (err error) {
 		if err != nil {
 			return err
 		}
-		if c.CertChain == "" {
-			// If no certChain is passed, the Fulcio root certificate will be used
+		switch {
+		case c.CertChain == "" && co.RootCerts == nil:
+			// If no certChain and no CARoots are passed, the Fulcio root certificate will be used
 			co.RootCerts, err = fulcio.GetRoots()
 			if err != nil {
 				return fmt.Errorf("getting Fulcio roots: %w", err)
@@ -251,7 +278,7 @@ func (c *VerifyCommand) Exec(ctx context.Context, images []string) (err error) {
 			if err != nil {
 				return err
 			}
-		} else {
+		case c.CertChain != "":
 			// Verify certificate with chain
 			chain, err := loadCertChainFromFileOrURL(c.CertChain)
 			if err != nil {
@@ -261,14 +288,26 @@ func (c *VerifyCommand) Exec(ctx context.Context, images []string) (err error) {
 			if err != nil {
 				return err
 			}
+		case co.RootCerts != nil:
+			// Verify certificate with root (and if given, intermediate) certificate
+			pubKey, err = cosign.ValidateAndUnpackCert(cert, co)
+			if err != nil {
+				return err
+			}
+		default:
+			return errors.New("internal error in handling CertChain and RootCerts - default case should never happen")
 		}
+
 		if c.SCTRef != "" {
 			sct, err := os.ReadFile(filepath.Clean(c.SCTRef))
 			if err != nil {
 				return fmt.Errorf("reading sct from file: %w", err)
 			}
 			co.SCT = sct
 		}
+	default:
+		// Do nothing. Neither keyRef, c.Sk, nor certRef were set - can happen for example when using Fulcio and TSA.
+		// For an example see the TestAttachWithRFC3161Timestamp test in test/e2e_test.go.
 	}
 	co.SigVerifier = pubKey