Upgrade to TUF v2 client with trusted root

Use sigstore-go's TUF client to fetch the trusted_root.json from the TUF
mirror, if available. Where possible, use sigstore-go's verifiers which
natively accept the trusted root as its trusted material. Where there is
no trusted root available in TUF or sigstore-go doesn't support a use
case, fall back to the sigstore/sigstore TUF v1 client and the existing
verifiers in cosign.

Signed-off-by: Colleen Murphy <colleenmurphy@google.com>

cmd/cosign/cli/fulcio/fulcioverifier/fulcioverifier.go

@@ -23,6 +23,8 @@ import (
 	"github.com/sigstore/cosign/v2/cmd/cosign/cli/options"
 	"github.com/sigstore/cosign/v2/internal/ui"
 	"github.com/sigstore/cosign/v2/pkg/cosign"
+	"github.com/sigstore/sigstore-go/pkg/verify"
+	"github.com/sigstore/sigstore/pkg/cryptoutils"
 	"github.com/sigstore/sigstore/pkg/signature"
 )
 
@@ -32,12 +34,26 @@ func NewSigner(ctx context.Context, ko options.KeyOpts, signer signature.SignerV
 		return nil, err
 	}
 
-	// Grab the PublicKeys for the CTFE, either from tuf or env.
+	if ko.TrustedMaterial != nil && len(fs.SCT) == 0 {
+		// We assume that if a trusted_root.json was found, the fulcio chain was included in it.
+		// fs.Chain will be ignored as root.VerifySignedCertificateTimestamp relies on the trusted root.
+		// Detached SCTs cannot be verified with this function.
+		certs, err := cryptoutils.UnmarshalCertificatesFromPEM(fs.Cert)
+		if err != nil || len(certs) < 1 {
+			return nil, fmt.Errorf("unmarshalling SCT from PEM: %w", err)
+		}
+		if err := verify.VerifySignedCertificateTimestamp(certs[0], 1, ko.TrustedMaterial); err != nil {
+			return nil, fmt.Errorf("verifying SCT using trusted root: %w", err)
+		}
+		ui.Infof(ctx, "Successfully verified SCT...")
+		return fs, nil
+	}
+
+	// There was no trusted_root.json or we need to verify a detached SCT, so grab the PublicKeys for the CTFE, either from tuf or env.
 	pubKeys, err := cosign.GetCTLogPubs(ctx)
 	if err != nil {
 		return nil, fmt.Errorf("getting CTFE public keys: %w", err)
 	}
-
 	// verify the sct
 	if err := cosign.VerifySCT(ctx, fs.Cert, fs.Chain, fs.SCT, pubKeys); err != nil {
 		return nil, fmt.Errorf("verifying SCT: %w", err)

cmd/cosign/cli/initialize/init.go

@@ -20,9 +20,14 @@ import (
 	_ "embed" // To enable the `go:embed` directive.
 	"encoding/json"
 	"fmt"
+	"os"
+	"path/filepath"
 
+	"github.com/sigstore/cosign/v2/internal/ui"
 	"github.com/sigstore/cosign/v2/pkg/blob"
-	"github.com/sigstore/sigstore/pkg/tuf"
+	tufroot "github.com/sigstore/sigstore-go/pkg/root"
+	"github.com/sigstore/sigstore-go/pkg/tuf"
+	tufv1 "github.com/sigstore/sigstore/pkg/tuf"
 )
 
 func DoInitialize(ctx context.Context, root, mirror string) error {
@@ -36,11 +41,36 @@ func DoInitialize(ctx context.Context, root, mirror string) error {
 		}
 	}
 
-	if err := tuf.Initialize(ctx, mirror, rootFileBytes); err != nil {
+	opts := tuf.DefaultOptions()
+	if root != "" {
+		opts.Root = rootFileBytes
+	}
+	if mirror != "" {
+		opts.RepositoryBaseURL = mirror
+	}
+	trustedRoot, err := tufroot.NewLiveTrustedRoot(opts)
+	if err != nil {
+		ui.Warnf(ctx, "Could not find trusted_root.json in TUF mirror, falling back to individual targets. It is recommended to update your TUF metadata repository to include trusted_root.json.")
+	}
+	// Leave a hint for where the current remote is. Adopted from sigstore/sigstore TUF client.
+	remote := map[string]string{"remote": opts.RepositoryBaseURL}
+	remoteBytes, err := json.Marshal(remote)
+	if err != nil {
+		return err
+	}
+	if err := os.WriteFile(filepath.FromSlash(filepath.Join(opts.CachePath, "remote.json")), remoteBytes, 0o600); err != nil {
+		return fmt.Errorf("storing remote: %w", err)
+	}
+	if trustedRoot != nil {
+		return nil
+	}
+
+	// The mirror did not have a trusted_root.json, so initialize the legacy TUF targets.
+	if err := tufv1.Initialize(ctx, mirror, rootFileBytes); err != nil {
 		return err
 	}
 
-	status, err := tuf.GetRootStatus(ctx)
+	status, err := tufv1.GetRootStatus(ctx)
 	if err != nil {
 		return err
 	}

cmd/cosign/cli/options/key.go

@@ -15,7 +15,10 @@
 
 package options
 
-import "github.com/sigstore/cosign/v2/pkg/cosign"
+import (
+	"github.com/sigstore/cosign/v2/pkg/cosign"
+	"github.com/sigstore/sigstore-go/pkg/root"
+)
 
 type KeyOpts struct {
 	Sk                   bool
@@ -53,4 +56,7 @@ type KeyOpts struct {
 	// Modeled after InsecureSkipVerify in tls.Config, this disables
 	// verifying the SCT.
 	InsecureSkipFulcioVerify bool
+
+	// TrustedMaterial contains trusted metadata for all Sigstore services. It is exclusive with RekorPubKeys, RootCerts, IntermediateCerts, CTLogPubKeys, and the TSA* cert fields.
+	TrustedMaterial root.TrustedMaterial
 }

cmd/cosign/cli/sign.go

@@ -24,6 +24,7 @@ import (
 	"github.com/sigstore/cosign/v2/cmd/cosign/cli/generate"
 	"github.com/sigstore/cosign/v2/cmd/cosign/cli/options"
 	"github.com/sigstore/cosign/v2/cmd/cosign/cli/sign"
+	"github.com/sigstore/cosign/v2/pkg/cosign"
 )
 
 func Sign() *cobra.Command {
@@ -103,6 +104,9 @@ race conditions or (worse) malicious tampering.
 			if err != nil {
 				return err
 			}
+
+			trustedMaterial, _ := cosign.TrustedRoot()
+
 			ko := options.KeyOpts{
 				KeyRef:                         o.Key,
 				PassFunc:                       generate.GetPass,
@@ -126,6 +130,7 @@ race conditions or (worse) malicious tampering.
 				TSAServerName:                  o.TSAServerName,
 				TSAServerURL:                   o.TSAServerURL,
 				IssueCertificateForExistingKey: o.IssueCertificate,
+				TrustedMaterial:                trustedMaterial,
 			}
 			if err := sign.SignCmd(ro, ko, *o, args); err != nil {
 				if o.Attachment == "" {

cmd/cosign/cli/sign/sign.go

@@ -54,6 +54,7 @@ import (
 	ociremote "github.com/sigstore/cosign/v2/pkg/oci/remote"
 	"github.com/sigstore/cosign/v2/pkg/oci/walk"
 	sigs "github.com/sigstore/cosign/v2/pkg/signature"
+	"github.com/sigstore/sigstore-go/pkg/root"
 	"github.com/sigstore/sigstore/pkg/cryptoutils"
 	"github.com/sigstore/sigstore/pkg/signature"
 	signatureoptions "github.com/sigstore/sigstore/pkg/signature/options"
@@ -391,7 +392,7 @@ func signerFromSecurityKey(ctx context.Context, keySlot string) (*SignerVerifier
 	}, nil
 }
 
-func signerFromKeyRef(ctx context.Context, certPath, certChainPath, keyRef string, passFunc cosign.PassFunc) (*SignerVerifier, error) {
+func signerFromKeyRef(ctx context.Context, certPath, certChainPath, keyRef string, passFunc cosign.PassFunc, trustedMaterial root.TrustedMaterial) (*SignerVerifier, error) {
 	k, err := sigs.SignerVerifierFromKeyRef(ctx, keyRef, passFunc)
 	if err != nil {
 		return nil, fmt.Errorf("reading key: %w", err)
@@ -505,9 +506,14 @@ func signerFromKeyRef(ctx context.Context, certPath, certChainPath, keyRef strin
 		return nil, err
 	}
 	if contains {
-		pubKeys, err := cosign.GetCTLogPubs(ctx)
-		if err != nil {
-			return nil, fmt.Errorf("getting CTLog public keys: %w", err)
+		var pubKeys any
+		if trustedMaterial != nil {
+			pubKeys = trustedMaterial.CTLogs()
+		} else {
+			pubKeys, err = cosign.GetCTLogPubs(ctx)
+			if err != nil {
+				return nil, fmt.Errorf("getting CTLog public keys: %w", err)
+			}
 		}
 		var chain []*x509.Certificate
 		chain = append(chain, leafCert)
@@ -567,7 +573,7 @@ func SignerFromKeyOpts(ctx context.Context, certPath string, certChainPath strin
 	case ko.Sk:
 		sv, err = signerFromSecurityKey(ctx, ko.Slot)
 	case ko.KeyRef != "":
-		sv, err = signerFromKeyRef(ctx, certPath, certChainPath, ko.KeyRef, ko.PassFunc)
+		sv, err = signerFromKeyRef(ctx, certPath, certChainPath, ko.KeyRef, ko.PassFunc, ko.TrustedMaterial)
 	default:
 		genKey = true
 		ui.Infof(ctx, "Generating ephemeral keys...")

cmd/cosign/cli/sign/sign_test.go

@@ -134,7 +134,7 @@ func Test_signerFromKeyRefSuccess(t *testing.T) {
 	ctx := context.Background()
 	keyFile, certFile, chainFile, privKey, cert, chain := generateCertificateFiles(t, tmpDir, pass("foo"))
 
-	signer, err := signerFromKeyRef(ctx, certFile, chainFile, keyFile, pass("foo"))
+	signer, err := signerFromKeyRef(ctx, certFile, chainFile, keyFile, pass("foo"), nil)
 	if err != nil {
 		t.Fatalf("unexpected error generating signer: %v", err)
 	}
@@ -173,17 +173,17 @@ func Test_signerFromKeyRefFailure(t *testing.T) {
 	_, certFile2, chainFile2, _, _, _ := generateCertificateFiles(t, tmpDir2, pass("bar"))
 
 	// Public keys don't match
-	_, err := signerFromKeyRef(ctx, certFile2, chainFile2, keyFile, pass("foo"))
+	_, err := signerFromKeyRef(ctx, certFile2, chainFile2, keyFile, pass("foo"), nil)
 	if err == nil || err.Error() != "public key in certificate does not match the provided public key" {
 		t.Fatalf("expected mismatched keys error, got %v", err)
 	}
 	// Certificate chain cannot be verified
-	_, err = signerFromKeyRef(ctx, certFile, chainFile2, keyFile, pass("foo"))
+	_, err = signerFromKeyRef(ctx, certFile, chainFile2, keyFile, pass("foo"), nil)
 	if err == nil || !strings.Contains(err.Error(), "unable to validate certificate chain") {
 		t.Fatalf("expected chain verification error, got %v", err)
 	}
 	// Certificate chain specified without certificate
-	_, err = signerFromKeyRef(ctx, "", chainFile2, keyFile, pass("foo"))
+	_, err = signerFromKeyRef(ctx, "", chainFile2, keyFile, pass("foo"), nil)
 	if err == nil || !strings.Contains(err.Error(), "no leaf certificate found or provided while specifying chain") {
 		t.Fatalf("expected no leaf error, got %v", err)
 	}
@@ -203,7 +203,7 @@ func Test_signerFromKeyRefFailureEmptyChainFile(t *testing.T) {
 		t.Fatalf("failed to write chain file: %v", err)
 	}
 
-	_, err = signerFromKeyRef(ctx, certFile, tmpChainFile.Name(), keyFile, pass("foo"))
+	_, err = signerFromKeyRef(ctx, certFile, tmpChainFile.Name(), keyFile, pass("foo"), nil)
 	if err == nil || err.Error() != "no certificates in certificate chain" {
 		t.Fatalf("expected empty chain error, got %v", err)
 	}

cmd/cosign/cli/signblob.go

@@ -22,6 +22,7 @@ import (
 	"github.com/sigstore/cosign/v2/cmd/cosign/cli/generate"
 	"github.com/sigstore/cosign/v2/cmd/cosign/cli/options"
 	"github.com/sigstore/cosign/v2/cmd/cosign/cli/sign"
+	"github.com/sigstore/cosign/v2/pkg/cosign"
 	"github.com/spf13/cobra"
 	"github.com/spf13/viper"
 )
@@ -68,6 +69,7 @@ func SignBlob() *cobra.Command {
 			if err != nil {
 				return err
 			}
+			trustedMaterial, _ := cosign.TrustedRoot()
 			ko := options.KeyOpts{
 				KeyRef:                         o.Key,
 				PassFunc:                       generate.GetPass,
@@ -93,6 +95,7 @@ func SignBlob() *cobra.Command {
 				TSAServerURL:                   o.TSAServerURL,
 				RFC3161TimestampPath:           o.RFC3161TimestampPath,
 				IssueCertificateForExistingKey: o.IssueCertificate,
+				TrustedMaterial:                trustedMaterial,
 			}
 
 			for _, blob := range args {

cmd/cosign/cli/verify/verify.go

@@ -37,6 +37,7 @@ import (
 	"github.com/sigstore/cosign/v2/internal/ui"
 	"github.com/sigstore/cosign/v2/pkg/blob"
 	"github.com/sigstore/cosign/v2/pkg/cosign"
+	"github.com/sigstore/cosign/v2/pkg/cosign/env"
 	"github.com/sigstore/cosign/v2/pkg/cosign/pivkey"
 	"github.com/sigstore/cosign/v2/pkg/cosign/pkcs11key"
 	"github.com/sigstore/cosign/v2/pkg/oci"
@@ -128,6 +129,16 @@ func (c *VerifyCommand) Exec(ctx context.Context, images []string) (err error) {
 		return fmt.Errorf("constructing client options: %w", err)
 	}
 
+	trustedMaterial, _ := cosign.TrustedRoot()
+	if options.NOf(c.CertChain, c.CARoots, c.CAIntermediates, c.TSACertChainPath) > 0 ||
+		env.Getenv(env.VariableSigstoreCTLogPublicKeyFile) != "" ||
+		env.Getenv(env.VariableSigstoreRootFile) != "" ||
+		env.Getenv(env.VariableSigstoreRekorPublicKey) != "" ||
+		env.Getenv(env.VariableSigstoreTSACertificateFile) != "" {
+		// trusted_root.json was found, but a cert chain was explicitly provided, so don't overrule the user's intentions.
+		trustedMaterial = nil
+	}
+
 	co := &cosign.CheckOpts{
 		Annotations:                  c.Annotations.Annotations,
 		RegistryClientOpts:           ociremoteOpts,
@@ -144,6 +155,7 @@ func (c *VerifyCommand) Exec(ctx context.Context, images []string) (err error) {
 		IgnoreTlog:                   c.IgnoreTlog,
 		MaxWorkers:                   c.MaxWorkers,
 		ExperimentalOCI11:            c.ExperimentalOCI11,
+		TrustedMaterial:              trustedMaterial,
 	}
 	if c.CheckClaims {
 		co.ClaimVerifier = cosign.SimpleClaimVerifier
@@ -167,11 +179,13 @@ func (c *VerifyCommand) Exec(ctx context.Context, images []string) (err error) {
 			}
 			co.RekorClient = rekorClient
 		}
-		// This performs an online fetch of the Rekor public keys, but this is needed
-		// for verifying tlog entries (both online and offline).
-		co.RekorPubKeys, err = cosign.GetRekorPubs(ctx)
-		if err != nil {
-			return fmt.Errorf("getting Rekor public keys: %w", err)
+		if co.TrustedMaterial == nil {
+			// This performs an online fetch of the Rekor public keys, but this is needed
+			// for verifying tlog entries (both online and offline).
+			co.RekorPubKeys, err = cosign.GetRekorPubs(ctx)
+			if err != nil {
+				return fmt.Errorf("getting Rekor public keys: %w", err)
+			}
 		}
 	}
 	if keylessVerification(c.KeyRef, c.Sk) {
@@ -184,7 +198,7 @@ func (c *VerifyCommand) Exec(ctx context.Context, images []string) (err error) {
 	certRef := c.CertRef
 
 	// Ignore Signed Certificate Timestamp if the flag is set or a key is provided
-	if shouldVerifySCT(c.IgnoreSCT, c.KeyRef, c.Sk) {
+	if co.TrustedMaterial == nil && shouldVerifySCT(c.IgnoreSCT, c.KeyRef, c.Sk) {
 		co.CTLogPubKeys, err = cosign.GetCTLogPubs(ctx)
 		if err != nil {
 			return fmt.Errorf("getting ctlog public keys: %w", err)
@@ -221,13 +235,15 @@ func (c *VerifyCommand) Exec(ctx context.Context, images []string) (err error) {
 		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)
-			}
-			co.IntermediateCerts, err = fulcio.GetIntermediates()
-			if err != nil {
-				return fmt.Errorf("getting Fulcio intermediates: %w", err)
+			if co.TrustedMaterial == nil {
+				co.RootCerts, err = fulcio.GetRoots()
+				if err != nil {
+					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 = cosign.ValidateAndUnpackCert(cert, co)
 			if err != nil {