Add ability for verify-blob to find signing cert in transparency log (#…

…991)

- Uses the first tlog entry it finds
- Verifies provided cert / public key. If one isn't provided by the
user, it will find it in the tlog (if experimental feature flag is
enabled)

Authored-by: Dennis Leon <[email protected]>
Signed-off-by: Dennis Leon <[email protected]>

cmd/cosign/cli/verify/verify_blob.go

@@ -27,8 +27,8 @@ import (
 	"io"
 	"os"
 
+	"github.com/go-openapi/runtime"
 	"github.com/pkg/errors"
-
 	"github.com/sigstore/cosign/cmd/cosign/cli/fulcio"
 	"github.com/sigstore/cosign/cmd/cosign/cli/options"
 	"github.com/sigstore/cosign/cmd/cosign/cli/sign"
@@ -37,6 +37,9 @@ import (
 	"github.com/sigstore/cosign/pkg/cosign/pivkey"
 	sigs "github.com/sigstore/cosign/pkg/signature"
 	rekorClient "github.com/sigstore/rekor/pkg/client"
+	"github.com/sigstore/rekor/pkg/generated/models"
+	"github.com/sigstore/rekor/pkg/types"
+	rekord "github.com/sigstore/rekor/pkg/types/rekord/v0.0.1"
 	"github.com/sigstore/sigstore/pkg/cryptoutils"
 	sigstoresigs "github.com/sigstore/sigstore/pkg/signature"
 	signatureoptions "github.com/sigstore/sigstore/pkg/signature/options"
@@ -53,10 +56,36 @@ func VerifyBlobCmd(ctx context.Context, ko sign.KeyOpts, certRef, sigRef, blobRe
 	var err error
 	var cert *x509.Certificate
 
-	if !options.OneOf(ko.KeyRef, ko.Sk, certRef) {
+	if !options.OneOf(ko.KeyRef, ko.Sk, certRef) && !options.EnableExperimental() {
 		return &options.PubKeyParseError{}
 	}
 
+	var b64sig string
+	targetSig, err := blob.LoadFileOrURL(sigRef)
+	if err != nil {
+		if !os.IsNotExist(err) {
+			// ignore if file does not exist, it can be a base64 encoded string as well
+			return err
+		}
+		targetSig = []byte(sigRef)
+	}
+
+	if isb64(targetSig) {
+		b64sig = string(targetSig)
+	} else {
+		b64sig = base64.StdEncoding.EncodeToString(targetSig)
+	}
+
+	var blobBytes []byte
+	if blobRef == "-" {
+		blobBytes, err = io.ReadAll(os.Stdin)
+	} else {
+		blobBytes, err = blob.LoadFileOrURL(blobRef)
+	}
+	if err != nil {
+		return err
+	}
+
 	// Keys are optional!
 	switch {
 	case ko.KeyRef != "":
@@ -92,32 +121,35 @@ func VerifyBlobCmd(ctx context.Context, ko sign.KeyOpts, certRef, sigRef, blobRe
 		if err != nil {
 			return err
 		}
-	}
+	case options.EnableExperimental():
+		rClient, err := rekorClient.GetRekorClient(ko.RekorURL)
+		if err != nil {
+			return err
+		}
 
-	var b64sig string
-	targetSig, err := blob.LoadFileOrURL(sigRef)
-	if err != nil {
-		if !os.IsNotExist(err) {
-			// ignore if file does not exist, it can be a base64 encoded string as well
+		uuids, err := cosign.FindTLogEntriesByPayload(rClient, blobBytes)
+		if err != nil {
 			return err
 		}
-		targetSig = []byte(sigRef)
-	}
 
-	if isb64(targetSig) {
-		b64sig = string(targetSig)
-	} else {
-		b64sig = base64.StdEncoding.EncodeToString(targetSig)
-	}
+		if len(uuids) == 0 {
+			return errors.New("could not find a tlog entry for provided blob")
+		}
 
-	var blobBytes []byte
-	if blobRef == "-" {
-		blobBytes, err = io.ReadAll(os.Stdin)
-	} else {
-		blobBytes, err = blob.LoadFileOrURL(blobRef)
-	}
-	if err != nil {
-		return err
+		tlogEntry, err := cosign.GetTlogEntry(rClient, uuids[0])
+		if err != nil {
+			return err
+		}
+
+		certs, err := extractCerts(tlogEntry)
+		if err != nil {
+			return err
+		}
+		cert = certs[0]
+		pubKey, err = sigstoresigs.LoadECDSAVerifier(cert.PublicKey.(*ecdsa.PublicKey), crypto.SHA256)
+		if err != nil {
+			return err
+		}
 	}
 
 	sig, err := base64.StdEncoding.DecodeString(b64sig)
@@ -165,3 +197,47 @@ func VerifyBlobCmd(ctx context.Context, ko sign.KeyOpts, certRef, sigRef, blobRe
 
 	return nil
 }
+
+func extractCerts(e *models.LogEntryAnon) ([]*x509.Certificate, error) {
+	b, err := base64.StdEncoding.DecodeString(e.Body.(string))
+	if err != nil {
+		return nil, err
+	}
+
+	pe, err := models.UnmarshalProposedEntry(bytes.NewReader(b), runtime.JSONConsumer())
+	if err != nil {
+		return nil, err
+	}
+
+	eimpl, err := types.NewEntry(pe)
+	if err != nil {
+		return nil, err
+	}
+
+	var v001Entry *rekord.V001Entry
+	var ok bool
+	if v001Entry, ok = eimpl.(*rekord.V001Entry); !ok {
+		return nil, errors.New("unexpected tlog entry type")
+	}
+
+	publicKeyB64, err := v001Entry.RekordObj.Signature.PublicKey.Content.MarshalText()
+	if err != nil {
+		return nil, err
+	}
+
+	publicKey, err := base64.StdEncoding.DecodeString(string(publicKeyB64))
+	if err != nil {
+		return nil, err
+	}
+
+	certs, err := cryptoutils.UnmarshalCertificatesFromPEM(publicKey)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(certs) == 0 {
+		return nil, errors.New("no certs found in pem tlog")
+	}
+
+	return certs, err
+}

pkg/cosign/tlog.go

@@ -17,6 +17,7 @@ package cosign
 import (
 	"bytes"
 	"context"
+	"crypto/sha256"
 	"encoding/base64"
 	"encoding/hex"
 	"fmt"
@@ -27,9 +28,10 @@ import (
 	"github.com/google/trillian/merkle/logverifier"
 	"github.com/google/trillian/merkle/rfc6962/hasher"
 	"github.com/pkg/errors"
-
 	"github.com/sigstore/cosign/pkg/cosign/tuf"
 	"github.com/sigstore/cosign/pkg/oci"
+	"github.com/sigstore/rekor/pkg/generated/client/index"
+
 	"github.com/sigstore/rekor/pkg/generated/client"
 	"github.com/sigstore/rekor/pkg/generated/client/entries"
 	"github.com/sigstore/rekor/pkg/generated/client/pubkey"
@@ -124,7 +126,7 @@ func rekorEntry(payload, signature, pubKey []byte) rekord_v001.V001Entry {
 	}
 }
 
-func getTlogEntry(rekorClient *client.Rekor, uuid string) (*models.LogEntryAnon, error) {
+func GetTlogEntry(rekorClient *client.Rekor, uuid string) (*models.LogEntryAnon, error) {
 	params := entries.NewGetLogEntryByUUIDParams()
 	params.SetEntryUUID(uuid)
 	resp, err := rekorClient.Entries.GetLogEntryByUUID(params)
@@ -177,6 +179,21 @@ func FindTlogEntry(rekorClient *client.Rekor, b64Sig string, payload, pubKey []b
 	return uuid, *verifiedEntry.Verification.InclusionProof.LogIndex, nil
 }
 
+func FindTLogEntriesByPayload(rekorClient *client.Rekor, payload []byte) (uuids []string, err error) {
+	params := index.NewSearchIndexParams()
+	params.Query = &models.SearchIndex{}
+
+	h := sha256.New()
+	h.Write(payload)
+	params.Query.Hash = fmt.Sprintf("sha256:%s", strings.ToLower(hex.EncodeToString(h.Sum(nil))))
+
+	searchIndex, err := rekorClient.Index.SearchIndex(params)
+	if err != nil {
+		return nil, err
+	}
+	return searchIndex.GetPayload(), nil
+}
+
 func verifyTLogEntry(rekorClient *client.Rekor, uuid string) (*models.LogEntryAnon, error) {
 	params := entries.NewGetLogEntryByUUIDParams()
 	params.EntryUUID = uuid

pkg/cosign/verify.go

@@ -260,7 +260,7 @@ func Verify(ctx context.Context, signedImgRef name.Reference, accessor Accessor,
 				// if we have a cert, we should check expiry
 				// The IntegratedTime verified in VerifyTlog
 				if cert != nil {
-					e, err := getTlogEntry(rekorClient, uuid)
+					e, err := GetTlogEntry(rekorClient, uuid)
 					if err != nil {
 						return err
 					}