Parse DSSE bundles and Intoto payloads

Signed-off-by: Appu Goundan <[email protected]>

Author: loosebazooka

sigstore-java/src/main/java/dev/sigstore/KeylessVerifier.java

@@ -122,7 +122,7 @@ public void verify(Path artifact, Bundle bundle, VerificationOptions options)
   public void verify(byte[] artifactDigest, Bundle bundle, VerificationOptions options)
       throws KeylessVerificationException {
 
-    if (bundle.getDSSESignature().isPresent()) {
+    if (bundle.getDsseEnvelope().isPresent()) {
       throw new KeylessVerificationException("Cannot verify DSSE signature based bundles");
     }
 

sigstore-java/src/main/java/dev/sigstore/bundle/Bundle.java

@@ -20,13 +20,16 @@
 import java.io.IOException;
 import java.io.Reader;
 import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.security.cert.CertPath;
 import java.util.List;
 import java.util.Optional;
+import org.immutables.gson.Gson;
 import org.immutables.value.Value;
 import org.immutables.value.Value.Default;
+import org.immutables.value.Value.Derived;
 import org.immutables.value.Value.Immutable;
 import org.immutables.value.Value.Lazy;
 
@@ -59,13 +62,13 @@ public String getMediaType() {
   public abstract Optional<MessageSignature> getMessageSignature();
 
   /** A DSSE envelope signature type that may contain an arbitrary payload */
-  public abstract Optional<DSSESignature> getDSSESignature();
+  public abstract Optional<DsseEnvelope> getDsseEnvelope();
 
   @Value.Check
   protected void checkOnlyOneSignature() {
     Preconditions.checkState(
-        (getDSSESignature().isEmpty() && getMessageSignature().isPresent())
-            || (getDSSESignature().isPresent() && getMessageSignature().isEmpty()));
+        (getDsseEnvelope().isEmpty() && getMessageSignature().isPresent())
+            || (getDsseEnvelope().isPresent() && getMessageSignature().isEmpty()));
   }
 
   @Value.Check
@@ -132,7 +135,7 @@ public interface MessageDigest {
   }
 
   @Immutable
-  public interface DSSESignature {
+  public interface DsseEnvelope {
 
     /** An arbitrary payload that does not need to be parsed to be validated */
     String getPayload();
@@ -141,7 +144,36 @@ public interface DSSESignature {
     String getPayloadType();
 
     /** DSSE specific signature */
-    byte[] getSignature();
+    List<Signature> getSignatures();
+
+    /**
+     * The "Pre-Authentication Encoding" of this statement. The signature is generated over this
+     * content.
+     */
+    @Gson.Ignore
+    @Derived
+    default byte[] getPAE() {
+      return ("DSSEv1 "
+              + getPayloadType().length()
+              + " "
+              + getPayloadType()
+              + " "
+              + getPayload().length()
+              + " "
+              + getPayload())
+          .getBytes(StandardCharsets.UTF_8);
+    }
+
+    @Lazy
+    @Gson.Ignore
+    default byte[] getSignature() {
+      return getSignatures().get(0).getSig();
+    }
+
+    @Immutable
+    interface Signature {
+      byte[] getSig();
+    }
   }
 
   @Immutable

sigstore-java/src/main/java/dev/sigstore/bundle/BundleReader.java

@@ -100,17 +100,18 @@ static Bundle readBundle(Reader jsonReader) throws BundleParseException {
     }
 
     if (protoBundle.hasDsseEnvelope()) {
-      var dsseEnvelope = protoBundle.getDsseEnvelope();
-      if (dsseEnvelope.getSignaturesCount() != 1) {
-        throw new BundleParseException("DSEE envelopes must contain exactly one signature");
+      var dsseEnvelopeProto = protoBundle.getDsseEnvelope();
+      var dsseEnvelopeBuilder =
+          ImmutableDsseEnvelope.builder()
+              .payload(dsseEnvelopeProto.getPayload().toStringUtf8())
+              .payloadType(dsseEnvelopeProto.getPayloadType());
+      for (int sigIndex = 0; sigIndex < dsseEnvelopeProto.getSignaturesCount(); sigIndex++) {
+        dsseEnvelopeBuilder.addSignatures(
+            ImmutableSignature.builder()
+                .sig(dsseEnvelopeProto.getSignatures(sigIndex).getSig().toByteArray())
+                .build());
       }
-      var dsseSignature =
-          ImmutableDSSESignature.builder()
-              .payload(dsseEnvelope.getPayload().toStringUtf8())
-              .payloadType(dsseEnvelope.getPayloadType())
-              .signature(dsseEnvelope.getSignatures(0).toByteArray())
-              .build();
-      bundleBuilder.dSSESignature(dsseSignature);
+      bundleBuilder.dsseEnvelope(dsseEnvelopeBuilder.build());
     } else if (protoBundle.hasMessageSignature()) {
       var signature = protoBundle.getMessageSignature().getSignature().toByteArray();
       if (protoBundle.getMessageSignature().hasMessageDigest()) {

sigstore-java/src/main/java/dev/sigstore/dsse/InTotoPayload.java

@@ -0,0 +1,57 @@
+/*
+ * 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 dev.sigstore.dsse;
+
+import static dev.sigstore.json.GsonSupplier.GSON;
+
+import com.google.gson.JsonElement;
+import dev.sigstore.bundle.Bundle.DsseEnvelope;
+import java.util.List;
+import java.util.Map;
+import org.immutables.gson.Gson;
+import org.immutables.value.Value.Immutable;
+
+@Gson.TypeAdapters
+@Immutable
+public interface InTotoPayload {
+
+  String PAYLOAD_TYPE = "application/vnd.in-toto+json";
+
+  @Gson.Named("_type")
+  String getType();
+
+  List<Subject> getSubject();
+
+  String getPredicateType();
+
+  /**
+   * Predicate is not processed by this library, if you want to inspect the contents of an
+   * attestation, you want to use an attestation parser.
+   */
+  JsonElement getPredicate();
+
+  @Immutable
+  interface Subject {
+
+    String getName();
+
+    Map<String, String> getDigest();
+  }
+
+  static InTotoPayload from(DsseEnvelope dsseEnvelope) {
+    return GSON.get().fromJson(dsseEnvelope.getPayload(), InTotoPayload.class);
+  }
+}

sigstore-java/src/main/java/dev/sigstore/json/GsonSupplier.java

@@ -16,6 +16,7 @@
 package dev.sigstore.json;
 
 import com.google.gson.*;
+import dev.sigstore.dsse.GsonAdaptersInTotoPayload;
 import dev.sigstore.rekor.client.GsonAdaptersRekorEntry;
 import dev.sigstore.rekor.client.GsonAdaptersRekorEntryBody;
 import dev.sigstore.tuf.model.*;
@@ -59,6 +60,7 @@ public enum GsonSupplier implements Supplier<Gson> {
           .registerTypeAdapterFactory(new GsonAdaptersTargetMeta())
           .registerTypeAdapterFactory(new GsonAdaptersTimestamp())
           .registerTypeAdapterFactory(new GsonAdaptersTimestampMeta())
+          .registerTypeAdapterFactory(new GsonAdaptersInTotoPayload())
           .disableHtmlEscaping()
           .create();
 

sigstore-java/src/test/java/dev/sigstore/bundle/BundleReaderTest.java

@@ -16,6 +16,7 @@
 package dev.sigstore.bundle;
 
 import com.google.common.io.Resources;
+import dev.sigstore.dsse.InTotoPayload;
 import java.io.InputStreamReader;
 import java.nio.charset.StandardCharsets;
 import org.junit.jupiter.api.Assertions;
@@ -81,7 +82,9 @@ public void readV3_1Bundle_noInclusion() {
   @Test
   public void readDSSEBundle() throws Exception {
     var bundle = readBundle("dev/sigstore/samples/bundles/bundle.dsse.sigstore");
-    Assertions.assertTrue(bundle.getDSSESignature().isPresent());
+    Assertions.assertTrue(bundle.getDsseEnvelope().isPresent());
+    var intotoPayload = InTotoPayload.from(bundle.getDsseEnvelope().get());
+    Assertions.assertEquals("https://slsa.dev/provenance/v1", intotoPayload.getPredicateType());
   }
 
   private Bundle readBundle(String resourcePath) throws Exception {