Verify the certificate chain against the Fulcio root trust by default

cmd/cosign/cli/options/certificate.go

@@ -37,7 +37,7 @@ var _ Interface = (*RekorOptions)(nil)
 // AddFlags implements Interface
 func (o *CertVerifyOptions) AddFlags(cmd *cobra.Command) {
 	cmd.Flags().StringVar(&o.Cert, "certificate", "",
-		"path to the public certificate")
+		"path to the public certificate. The certificate will be verified against the Fulcio roots if the --certificate-chain option is not passed.")
 
 	cmd.Flags().StringVar(&o.CertEmail, "certificate-email", "",
 		"the email expected in a valid Fulcio certificate")

cmd/cosign/cli/verify/verify.go

@@ -160,11 +160,16 @@ func (c *VerifyCommand) Exec(ctx context.Context, images []string) (err error) {
 			return err
 		}
 		if c.CertChain == "" {
-			err = cosign.CheckCertificatePolicy(cert, co)
+			// If no certChain is passed, the Fulcio root certificate will be used
+			co.RootCerts, err = fulcio.GetRoots()
 			if err != nil {
-				return err
+				return fmt.Errorf("getting Fulcio roots: %w", err)
+			}
+			co.IntermediateCerts, err = fulcio.GetIntermediates()
+			if err != nil {
+				return fmt.Errorf("getting Fulcio intermediates: %w", err)
 			}
-			pubKey, err = signature.LoadVerifier(cert.PublicKey, crypto.SHA256)
+			pubKey, err = cosign.ValidateAndUnpackCert(cert, co)
 			if err != nil {
 				return err
 			}

cmd/cosign/cli/verify/verify_attestation.go

@@ -17,7 +17,6 @@ package verify
 
 import (
 	"context"
-	"crypto"
 	"errors"
 	"flag"
 	"fmt"
@@ -28,7 +27,6 @@ import (
 	"github.com/sigstore/cosign/pkg/cosign/pkcs11key"
 	"github.com/sigstore/cosign/pkg/cosign/rego"
 	"github.com/sigstore/cosign/pkg/oci"
-	"github.com/sigstore/sigstore/pkg/signature"
 
 	"github.com/sigstore/cosign/cmd/cosign/cli/fulcio"
 	"github.com/sigstore/cosign/cmd/cosign/cli/options"
@@ -139,11 +137,16 @@ func (c *VerifyAttestationCommand) Exec(ctx context.Context, images []string) (e
 			return fmt.Errorf("loading certificate from reference: %w", err)
 		}
 		if c.CertChain == "" {
-			err = cosign.CheckCertificatePolicy(cert, co)
+			// If no certChain is passed, the Fulcio root certificate will be used
+			co.RootCerts, err = fulcio.GetRoots()
 			if err != nil {
-				return err
+				return fmt.Errorf("getting Fulcio roots: %w", err)
+			}
+			co.IntermediateCerts, err = fulcio.GetIntermediates()
+			if err != nil {
+				return fmt.Errorf("getting Fulcio intermediates: %w", err)
 			}
-			co.SigVerifier, err = signature.LoadVerifier(cert.PublicKey, crypto.SHA256)
+			co.SigVerifier, err = cosign.ValidateAndUnpackCert(cert, co)
 			if err != nil {
 				return fmt.Errorf("creating certificate verifier: %w", err)
 			}

cmd/cosign/cli/verify/verify_blob.go

@@ -119,11 +119,16 @@ func VerifyBlobCmd(ctx context.Context, ko options.KeyOpts, certRef, certEmail,
 			EnforceSCT:                   enforceSCT,
 		}
 		if certChain == "" {
-			err = cosign.CheckCertificatePolicy(cert, co)
+			// If no certChain is passed, the Fulcio root certificate will be used
+			co.RootCerts, err = fulcio.GetRoots()
 			if err != nil {
-				return err
+				return fmt.Errorf("getting Fulcio roots: %w", err)
 			}
-			verifier, err = signature.LoadVerifier(cert.PublicKey, crypto.SHA256)
+			co.IntermediateCerts, err = fulcio.GetIntermediates()
+			if err != nil {
+				return fmt.Errorf("getting Fulcio intermediates: %w", err)
+			}
+			verifier, err = cosign.ValidateAndUnpackCert(cert, co)
 			if err != nil {
 				return err
 			}