Dsse one sig

examples/sigstore-go-signing/main.go

@@ -111,9 +111,9 @@ func main() {
 
 	if *idToken != "" {
 		fulcioOpts := &sign.FulcioOptions{
-			BaseURL:        "https://fulcio.sigstage.dev",
-			Timeout:        time.Duration(30 * time.Second),
-			Retries:        1,
+			BaseURL: "https://fulcio.sigstage.dev",
+			Timeout: time.Duration(30 * time.Second),
+			Retries: 1,
 		}
 		opts.CertificateProvider = sign.NewFulcio(fulcioOpts)
 		opts.CertificateProviderOptions = &sign.CertificateProviderOptions{
@@ -123,9 +123,9 @@ func main() {
 
 	if *tsa {
 		tsaOpts := &sign.TimestampAuthorityOptions{
-			URL:            "https://timestamp.githubapp.com/api/v1/timestamp",
-			Timeout:        time.Duration(30 * time.Second),
-			Retries:        1,
+			URL:     "https://timestamp.githubapp.com/api/v1/timestamp",
+			Timeout: time.Duration(30 * time.Second),
+			Retries: 1,
 		}
 		opts.TimestampAuthorities = append(opts.TimestampAuthorities, sign.NewTimestampAuthority(tsaOpts))
 
@@ -135,9 +135,9 @@ func main() {
 
 	if *rekor {
 		rekorOpts := &sign.RekorOptions{
-			BaseURL:        "https://rekor.sigstage.dev",
-			Timeout:        time.Duration(90 * time.Second),
-			Retries:        1,
+			BaseURL: "https://rekor.sigstage.dev",
+			Timeout: time.Duration(90 * time.Second),
+			Retries: 1,
 		}
 		opts.TransparencyLogs = append(opts.TransparencyLogs, sign.NewRekor(rekorOpts))
 	}

pkg/testing/data/data.go

@@ -40,9 +40,14 @@ func Unmarshal[T any](t *testing.T, data []byte) T {
 //go:embed sigstoreBundle.json
 var SigstoreBundleRaw []byte
 
+//go:embed sigstoreBundle2Sig.json
+var SigstoreBundle2SigRaw []byte
+
 //go:embed sigstore.js@2.0.0-provenanceBundle.json
 var SigstoreJS200ProvenanceBundleRaw []byte
 
+// TestBundle creates *bundle.ProtobufBundle from a raw byte stream
+// containing a JSON encoded protobuf bundle.
 func TestBundle(t *testing.T, raw []byte) *bundle.ProtobufBundle {
 	var b protobundle.Bundle
 	err := protojson.Unmarshal(raw, &b)
@@ -56,15 +61,23 @@ func TestBundle(t *testing.T, raw []byte) *bundle.ProtobufBundle {
 	return bun
 }
 
-// SigstoreBundle returns a test *sigstore.Bundle
+// SigstoreBundle returns a test *sigstore.Bundle.
 func SigstoreBundle(t *testing.T) *bundle.ProtobufBundle {
 	return TestBundle(t, SigstoreBundleRaw)
 }
 
+// SigstoreBundle2Sig returns a test *sigstore.Bundle with two signatures.
+func SigstoreBundle2Sig(t *testing.T) *bundle.ProtobufBundle {
+	return TestBundle(t, SigstoreBundle2SigRaw)
+}
+
+// SigstoreJS200ProvenanceBundle returns a test *sigstore.Bundle that
+// contains a complete sigstore-js build provenance.
 func SigstoreJS200ProvenanceBundle(t *testing.T) *bundle.ProtobufBundle {
 	return TestBundle(t, SigstoreJS200ProvenanceBundleRaw)
 }
 
+// PublicGoodTrustedMaterialRoot retruns a *root.TrustedRoot for PGI.
 func PublicGoodTrustedMaterialRoot(t *testing.T) *root.TrustedRoot {
 	trustedrootJSON, _ := os.ReadFile("../../examples/trusted-root-public-good.json")
 	trustedRoot, _ := root.NewTrustedRootFromJSON(trustedrootJSON)

pkg/testing/data/sigstoreBundle2Sig.json

@@ -0,0 +1,52 @@
+{
+	"mediaType": "application/vnd.dev.sigstore.bundle+json;version=0.1",
+	"verificationMaterial": {
+		"tlogEntries": [
+			{
+				"logIndex": "6800908",
+				"logId": {
+					"keyId": "wNI9atQGlz+VWfO6LRygH4QUfY/8W4RFwiT5i5WRgB0="
+				},
+				"kindVersion": {
+					"kind": "intoto",
+					"version": "0.0.2"
+				},
+				"integratedTime": "1668034836",
+				"inclusionPromise": {
+					"signedEntryTimestamp": "MEYCIQCEx8HKsx9hobZjrNqHCSEJvjMEhc2wU2mUwkI7ButQHAIhAPevmw7piNjE2N1OWHmp9S5kBvlVIg93qu4i9yRaswur"
+				},
+				"canonicalizedBody": "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"
+			}
+		],
+		"timestampVerificationData": {
+			"rfc3161Timestamps": []
+		},
+		"x509CertificateChain": {
+			"certificates": [
+				{
+					"rawBytes": "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"
+				},
+				{
+					"rawBytes": "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"
+				},
+				{
+					"rawBytes": "MIIB9zCCAXygAwIBAgIUALZNAPFdxHPwjeDloDwyYChAO/4wCgYIKoZIzj0EAwMwKjEVMBMGA1UEChMMc2lnc3RvcmUuZGV2MREwDwYDVQQDEwhzaWdzdG9yZTAeFw0yMTEwMDcxMzU2NTlaFw0zMTEwMDUxMzU2NThaMCoxFTATBgNVBAoTDHNpZ3N0b3JlLmRldjERMA8GA1UEAxMIc2lnc3RvcmUwdjAQBgcqhkjOPQIBBgUrgQQAIgNiAAT7XeFT4rb3PQGwS4IajtLk3/OlnpgangaBclYpsYBr5i+4ynB07ceb3LP0OIOZdxexX69c5iVuyJRQ+Hz05yi+UF3uBWAlHpiS5sh0+H2GHE7SXrk1EC5m1Tr19L9gg92jYzBhMA4GA1UdDwEB/wQEAwIBBjAPBgNVHRMBAf8EBTADAQH/MB0GA1UdDgQWBBRYwB5fkUWlZql6zJChkyLQKsXF+jAfBgNVHSMEGDAWgBRYwB5fkUWlZql6zJChkyLQKsXF+jAKBggqhkjOPQQDAwNpADBmAjEAj1nHeXZp+13NWBNa+EDsDP8G1WWg1tCMWP/WHPqpaVo0jhsweNFZgSs0eE7wYI4qAjEA2WB9ot98sIkoF3vZYdd3/VtWB5b9TNMea7Ix/stJ5TfcLLeABLE4BNJOsQ4vnBHJ"
+				}
+			]
+		}
+	},
+	"dsseEnvelope": {
+		"payload": "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",
+		"payloadType": "application/vnd.in-toto+json",
+		"signatures": [
+			{
+				"sig": "MEUCIFc/ByLhCkR2YtAMbmJp202ZmZ4XVGXFKi7r+q7lsNDPAiEA/JwX2PilCLvkqE9NJMFKNn2C2j8cH/zyFhQ65wri2HY=",
+				"keyid": ""
+			},
+			{
+				"sig": "MEUCIFc/ByLhCkR2YtAMbmJp202ZmZ4XVGXFKi7r+q7lsNDPAiEA/JwX2PilCLvkqE9NJMFKNn2C2j8cH/zyFhAAAAAAAHY=",
+				"keyid": ""
+			}
+		]
+	}
+}

pkg/verify/dsse_test.go

@@ -0,0 +1,124 @@
+// Copyright 2024 The Sigstore Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package verify
+
+import (
+	"context"
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/sha256"
+	"errors"
+	"fmt"
+	"testing"
+
+	"github.com/secure-systems-lab/go-securesystemslib/dsse"
+	"github.com/sigstore/sigstore/pkg/signature"
+	"github.com/stretchr/testify/assert"
+)
+
+type dsseSigner struct {
+	pk *ecdsa.PrivateKey
+}
+
+func (d *dsseSigner) Sign(_ context.Context, data []byte) ([]byte, error) {
+	digest := sha256.Sum256(data)
+	return d.pk.Sign(rand.Reader, digest[:], nil)
+}
+
+func (d *dsseSigner) KeyID() (string, error) {
+	return "", nil
+}
+
+type envelopeContent struct {
+	EnvelopeContent
+	e *dsse.Envelope
+}
+
+func (e *envelopeContent) RawEnvelope() *dsse.Envelope {
+	return e.e
+}
+
+func TestVerifyEnvelope(t *testing.T) {
+	privk, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	pubk := privk.Public().(*ecdsa.PublicKey)
+	assert.NoError(t, err)
+
+	var s = dsseSigner{
+		pk: privk,
+	}
+
+	testcases := []struct {
+		count int
+		fail  bool
+	}{
+		{
+			count: 0,
+			fail:  true,
+		},
+		{
+			count: 1,
+			fail:  false,
+		},
+		{
+			count: 2,
+			fail:  true,
+		},
+	}
+
+	for _, tc := range testcases {
+		t.Run(fmt.Sprintf("Test DSSE verify with %d signatures", tc.count),
+			func(t *testing.T) {
+				var e *dsse.Envelope
+
+				if tc.count == 0 {
+					// Need to create the envelope manually
+					e = &dsse.Envelope{
+						PayloadType: "test-payload-type",
+						// b64(test-payload)
+						Payload: "dGVzdC1wYXlsb2Fk",
+					}
+				} else {
+					var signers []dsse.Signer
+
+					for i := 0; i < tc.count; i++ {
+						signers = append(signers, &s)
+					}
+
+					es, err := dsse.NewEnvelopeSigner(signers...)
+					assert.NoError(t, err)
+					e, err = es.SignPayload(context.Background(),
+						"test-payload-type",
+						[]byte("test-payload"))
+					assert.NoError(t, err)
+				}
+				sigver, err := signature.LoadECDSAVerifier(pubk, crypto.SHA256)
+				assert.NoError(t, err)
+				err = verifyEnvelope(
+					sigver,
+					&envelopeContent{
+						e: e,
+					},
+				)
+
+				if tc.fail {
+					assert.True(t, errors.Is(err, ErrInvSigCount))
+				} else {
+					assert.NoError(t, err)
+				}
+			})
+	}
+}

pkg/verify/signature.go

@@ -31,6 +31,8 @@ import (
 	"github.com/sigstore/sigstore/pkg/signature/options"
 )
 
+var ErrInvSigCount = errors.New("exactly one signature is required")
+
 func VerifySignature(sigContent SignatureContent, verificationContent VerificationContent, trustedMaterial root.TrustedMaterial) error { // nolint: revive
 	var verifier signature.Verifier
 	var err error
@@ -100,6 +102,13 @@ func getSignatureVerifier(verificationContent VerificationContent, tm root.Trust
 }
 
 func verifyEnvelope(verifier signature.Verifier, envelope EnvelopeContent) error {
+	dsseEnv := envelope.RawEnvelope()
+
+	// A DSSE envelope in a Sigstore bundle MUST only contain one
+	// signature, even though DSSE is more permissive.
+	if len(dsseEnv.Signatures) != 1 {
+		return ErrInvSigCount
+	}
 	pub, err := verifier.PublicKey()
 	if err != nil {
 		return fmt.Errorf("could not fetch verifier public key: %w", err)
@@ -113,7 +122,7 @@ func verifyEnvelope(verifier signature.Verifier, envelope EnvelopeContent) error
 		return fmt.Errorf("could not load envelope verifier: %w", err)
 	}
 
-	_, err = envVerifier.Verify(context.TODO(), envelope.RawEnvelope())
+	_, err = envVerifier.Verify(context.TODO(), dsseEnv)
 	if err != nil {
 		return fmt.Errorf("could not verify envelope: %w", err)
 	}

pkg/verify/signed_entity_test.go

@@ -15,6 +15,7 @@
 package verify_test
 
 import (
+	"errors"
 	"strings"
 	"testing"
 	"unicode"
@@ -367,3 +368,15 @@ func ensureKeysBeginWithLowercase(t *testing.T, obj interface{}) {
 		}
 	}
 }
+
+func TestSigstoreBundle2Sig(t *testing.T) {
+	tr := data.PublicGoodTrustedMaterialRoot(t)
+	entity := data.SigstoreBundle2Sig(t)
+
+	v, err := verify.NewSignedEntityVerifier(tr, verify.WithTransparencyLog(1), verify.WithObserverTimestamps(1))
+	assert.NoError(t, err)
+
+	res, err := v.Verify(entity, SkipArtifactAndIdentitiesPolicy)
+	assert.True(t, errors.Is(err, verify.ErrInvSigCount))
+	assert.Nil(t, res)
+}