Store attestations in the layer (payload) rather than the annotation.

These can be quite large, especially when they are SBOMs.

Signed-off-by: Dan Lorenc <dlorenc@google.com>

cmd/cosign/cli/attest.go

@@ -218,7 +218,9 @@ func AttestCmd(ctx context.Context, ko KeyOpts, imageRef string, certPath string
 	}
 
 	fmt.Fprintln(os.Stderr, "Pushing attestation to:", attRef.String())
-	if _, err = cremote.UploadSignature(sig, payload, attRef, uo); err != nil {
+	// An attestation represents both the signature and payload. So store the entire thing
+	// in the payload field since they can get large
+	if _, err = cremote.UploadSignature([]byte{}, sig, attRef, uo); err != nil {
 		return errors.Wrap(err, "uploading")
 	}
 

cmd/cosign/cli/verify_attestation.go

@@ -18,6 +18,7 @@ package cli
 import (
 	"context"
 	"flag"
+	"io"
 
 	"github.com/google/go-containerregistry/pkg/name"
 	"github.com/peterbourgon/ff/v3/ffcli"
@@ -93,6 +94,17 @@ EXAMPLES
 	}
 }
 
+// DSSE messages contain the signature and payload in one object, but our interface expects a signature and payload
+// This means we need to use one field and ignore the other. The DSSE verifier upstream uses the signature field and ignores
+// The message field, but we want the reverse here.
+type reverseDSSEVerifier struct {
+	signature.Verifier
+}
+
+func (w *reverseDSSEVerifier) VerifySignature(s io.Reader, m io.Reader, opts ...signature.VerifyOption) error {
+	return w.Verifier.VerifySignature(m, nil, opts...)
+}
+
 // Exec runs the verification command
 func (c *VerifyAttestationCommand) Exec(ctx context.Context, args []string) (err error) {
 	if len(args) == 0 {
@@ -134,7 +146,10 @@ func (c *VerifyAttestationCommand) Exec(ctx context.Context, args []string) (err
 			return errors.Wrap(err, "initializing piv token verifier")
 		}
 	}
-	co.SigVerifier = dsse.WrapVerifier(pubKey)
+
+	co.SigVerifier = &reverseDSSEVerifier{
+		Verifier: dsse.WrapVerifier(pubKey),
+	}
 
 	for _, imageRef := range args {
 		ref, err := name.ParseReference(imageRef)

pkg/cosign/verifiers.go

@@ -16,10 +16,12 @@
 package cosign
 
 import (
+	"encoding/base64"
 	"encoding/json"
 
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/in-toto/in-toto-golang/in_toto"
+	"github.com/in-toto/in-toto-golang/pkg/ssl"
 	"github.com/pkg/errors"
 	"github.com/sigstore/sigstore/pkg/signature/payload"
 )
@@ -45,11 +47,20 @@ func SimpleClaimVerifier(sp SignedPayload, imageDigest v1.Hash, annotations map[
 
 // IntotoSubjectClaimVerifier verifies that SignedPayload.Payload is an Intoto statement which references the given image digest.
 func IntotoSubjectClaimVerifier(sp SignedPayload, imageDigest v1.Hash, _ map[string]interface{}) error {
-	st := &in_toto.Statement{}
-	if err := json.Unmarshal(sp.Payload, st); err != nil {
+	// The payload here is an envelope. We already verified the signature earlier.
+	e := ssl.Envelope{}
+	if err := json.Unmarshal(sp.Payload, &e); err != nil {
+		return err
+	}
+	stBytes, err := base64.StdEncoding.DecodeString(string(e.Payload))
+	if err != nil {
 		return err
 	}
 
+	st := in_toto.Statement{}
+	if err := json.Unmarshal(stBytes, &st); err != nil {
+		return err
+	}
 	for _, subj := range st.StatementHeader.Subject {
 		dgst, ok := subj.Digest["sha256"]
 		if !ok {