Handle parsing checkpoints from a rekor entry

This does not do validation on the checkpoint yet

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

sigstore-java/src/main/java/dev/sigstore/rekor/client/Checkpoints.java

@@ -0,0 +1,98 @@
+/*
+ * 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.rekor.client;
+
+import com.google.common.base.Splitter;
+import dev.sigstore.rekor.client.RekorEntry.Checkpoint;
+import dev.sigstore.rekor.client.RekorEntry.CheckpointSignature;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Base64;
+import java.util.List;
+import java.util.regex.Pattern;
+import java.util.stream.Collectors;
+
+/**
+ * Checkpoint helper class to parse from a string in the format described in
+ * https://github.com/transparency-dev/formats/blob/12bf59947efb7ae227c12f218b4740fb17a87e50/log/README.md
+ */
+class Checkpoints {
+  static Checkpoint from(String encoded) throws RekorParseException {
+    var split = Splitter.on("\n\n").splitToList(encoded);
+    if (split.size() != 2) {
+      throw new RekorParseException(
+          "Checkpoint must contain one blank line, delineating the header from the signature block");
+    }
+    var header = split.get(0);
+    var data = split.get(1);
+
+    // note that the string actually contains \n literally, not newlines
+    var headers = Splitter.on("\n").splitToList(header);
+    if (headers.size() < 3) {
+      throw new RekorParseException("Checkpoint header must contain at least 3 lines");
+    }
+
+    var origin = headers.get(0);
+    long size;
+    try {
+      size = Long.parseLong(headers.get(1));
+    } catch (NumberFormatException nfe) {
+      throw new RekorParseException("Checkpoint header attribute size must be a number");
+    }
+    var base64Hash = headers.get(2);
+    // we don't care about any other headers after this
+
+    if (data.length() == 0) {
+      throw new RekorParseException("Checkpoint body must contain at least one signature");
+    }
+    if (!data.endsWith("\n")) {
+      throw new RekorParseException("Checkpoint signature section must end with newline");
+    }
+
+    List<CheckpointSignature> signatures = new ArrayList<>();
+    for (String sig : data.lines().collect(Collectors.toList())) {
+      signatures.add(sigFrom(sig));
+    }
+
+    return ImmutableCheckpoint.builder()
+        .origin(origin)
+        .size(size)
+        .base64Hash(base64Hash)
+        .addAllSignatures(signatures)
+        .build();
+  }
+
+  static CheckpointSignature sigFrom(String signatureLine) throws RekorParseException {
+    var sigBlock = Pattern.compile("\\u2014 (\\S+) (\\S+)");
+    var m = sigBlock.matcher(signatureLine);
+    if (!m.find()) {
+      // really shouldn't be getting here because we check
+      throw new RekorParseException("Checkpoint signature was invalid or improperly formatted");
+    }
+    var identity = m.group(1);
+    var keySig = Base64.getDecoder().decode(m.group(2));
+    if (keySig.length < 5) {
+      throw new RekorParseException("Checkpoint signature contains too few bytes");
+    }
+    var keyHint = Arrays.copyOfRange(keySig, 0, 4);
+    var signature = Arrays.copyOfRange(keySig, 4, keySig.length);
+    return ImmutableCheckpointSignature.builder()
+        .identity(identity)
+        .keyHint(keyHint)
+        .signature(signature)
+        .build();
+  }
+}

sigstore-java/src/main/java/dev/sigstore/rekor/client/RekorEntry.java

@@ -25,6 +25,7 @@
 import org.immutables.gson.Gson;
 import org.immutables.value.Value;
 import org.immutables.value.Value.Derived;
+import org.immutables.value.Value.Lazy;
 
 /** A local representation of a rekor entry in the log. */
 @Gson.TypeAdapters
@@ -68,6 +69,44 @@ interface InclusionProof {
 
     /** The checkpoint (signed tree head) that the inclusion proof is based on. */
     String getCheckpoint();
+
+    /**
+     * The checkpoint that {@link #getCheckpoint} provides, but parsed into component parts.
+     *
+     * @return a Checkpoint
+     * @throws RekorParseException if the checkpoint is invalid
+     */
+    @Lazy
+    default Checkpoint parsedCheckpoint() throws RekorParseException {
+      return Checkpoints.from(getCheckpoint());
+    }
+  }
+
+  @Value.Immutable
+  interface Checkpoint {
+    /** Unique identity for the log. */
+    String getOrigin();
+
+    /** Size of the log for this checkpoint. */
+    Long getSize();
+
+    /** Log root hash at the defined log size. */
+    String getBase64Hash();
+
+    /** A list of signatures associated with the checkpoint. */
+    List<CheckpointSignature> getSignatures();
+  }
+
+  @Value.Immutable
+  interface CheckpointSignature {
+    /** Human readable log identity */
+    String getIdentity();
+
+    /** First 4 bytes of sha256 key hash as a Public Key hint. */
+    byte[] getKeyHint();
+
+    /** Signature over the tree head. */
+    byte[] getSignature();
   }
 
   /** Returns the content of the log entry. */

sigstore-java/src/test/java/dev/sigstore/rekor/client/CheckpointsTest.java

@@ -0,0 +1,147 @@
+/*
+ * 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.rekor.client;
+
+import com.google.common.io.Resources;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.util.Arrays;
+import java.util.Base64;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class CheckpointsTest {
+
+  public static final String REKOR_PUB_KEYID = "wNI9atQGlz+VWfO6LRygH4QUfY/8W4RFwiT5i5WRgB0=";
+
+  public String getResource(String filename) throws IOException {
+    return Resources.toString(
+        Resources.getResource("dev/sigstore/samples/checkpoints/" + filename),
+        StandardCharsets.UTF_8);
+  }
+
+  @Test
+  public void from_valid() throws Exception {
+    var checkpoint = Checkpoints.from(getResource("valid.txt"));
+    Assertions.assertEquals("rekor.sigstore.dev - 2605736670972794746", checkpoint.getOrigin());
+    Assertions.assertEquals(37795272, checkpoint.getSize());
+    Assertions.assertEquals(
+        "60ll7idWI1jYRZzxc+jKflYoW+4jWxgZaGR15ASsWt4=", checkpoint.getBase64Hash());
+
+    var keyBytesHintExpected =
+        Arrays.copyOfRange(Base64.getDecoder().decode(REKOR_PUB_KEYID), 0, 4);
+    var sig = checkpoint.getSignatures().get(0);
+    Assertions.assertEquals(1, checkpoint.getSignatures().size());
+    Assertions.assertEquals("rekor.sigstore.dev", sig.getIdentity());
+    Assertions.assertArrayEquals(keyBytesHintExpected, sig.getKeyHint());
+    Assertions.assertEquals(
+        "MEYCIQCVZQfYdI9rogwhEGAVwhemHcyP3EzvRZHRVUAO8YiX+gIhAKB+9RSNH9fmN7CWqkBYjw24kiJwqlMbri+jpQzl+lKB",
+        Base64.getEncoder().encodeToString(sig.getSignature()));
+  }
+
+  @Test
+  public void from_validMultiSig() throws Exception {
+    var checkpoint = Checkpoints.from(getResource("valid_multi_sig.txt"));
+    Assertions.assertEquals("rekor.sigstore.dev - 2605736670972794746", checkpoint.getOrigin());
+    Assertions.assertEquals(37795272, checkpoint.getSize());
+    Assertions.assertEquals(
+        "60ll7idWI1jYRZzxc+jKflYoW+4jWxgZaGR15ASsWt4=", checkpoint.getBase64Hash());
+
+    Assertions.assertEquals(2, checkpoint.getSignatures().size());
+    var keyBytesHintExpected =
+        Arrays.copyOfRange(Base64.getDecoder().decode(REKOR_PUB_KEYID), 0, 4);
+
+    var sig1 = checkpoint.getSignatures().get(0);
+    Assertions.assertEquals("rekor.sigstore.dev", sig1.getIdentity());
+    Assertions.assertArrayEquals(keyBytesHintExpected, sig1.getKeyHint());
+    Assertions.assertEquals(
+        "MEYCIQCVZQfYdI9rogwhEGAVwhemHcyP3EzvRZHRVUAO8YiX+gIhAKB+9RSNH9fmN7CWqkBYjw24kiJwqlMbri+jpQzl+lKB",
+        Base64.getEncoder().encodeToString(sig1.getSignature()));
+
+    var sig2 = checkpoint.getSignatures().get(1);
+    Assertions.assertEquals("bob.loblaw.dev", sig2.getIdentity());
+    Assertions.assertArrayEquals(keyBytesHintExpected, sig2.getKeyHint());
+    Assertions.assertEquals(
+        "MEYCIQCVZQfYdI9rogwhEGAVwhGmHcyP3EzvRZHRVUAO8YiX+gIhAKB+9RSNH9fmN7CWqkBYjw24kiJwqlMbri+jpQzl+lKB",
+        Base64.getEncoder().encodeToString(sig2.getSignature()));
+  }
+
+  @Test
+  public void from_noSeparator() throws Exception {
+    var ex =
+        Assertions.assertThrows(
+            RekorParseException.class,
+            () -> Checkpoints.from(getResource("error_header_body_separator.txt")));
+    Assertions.assertEquals(
+        "Checkpoint must contain one blank line, delineating the header from the signature block",
+        ex.getMessage());
+  }
+
+  @Test
+  public void from_notEnoughHeaders() throws Exception {
+    var ex =
+        Assertions.assertThrows(
+            RekorParseException.class,
+            () -> Checkpoints.from(getResource("error_header_count.txt")));
+    Assertions.assertEquals("Checkpoint header must contain at least 3 lines", ex.getMessage());
+  }
+
+  @Test
+  public void from_notANumber() throws Exception {
+    var ex =
+        Assertions.assertThrows(
+            RekorParseException.class,
+            () -> Checkpoints.from(getResource("error_not_a_number.txt")));
+    Assertions.assertEquals("Checkpoint header attribute size must be a number", ex.getMessage());
+  }
+
+  @Test
+  public void from_noSignatures() throws Exception {
+    var ex =
+        Assertions.assertThrows(
+            RekorParseException.class,
+            () -> Checkpoints.from(getResource("error_no_signatures.txt")));
+    Assertions.assertEquals("Checkpoint body must contain at least one signature", ex.getMessage());
+  }
+
+  @Test
+  public void from_noNewlineAfterSignatures() throws Exception {
+    var ex =
+        Assertions.assertThrows(
+            RekorParseException.class,
+            () -> Checkpoints.from(getResource("error_no_newline_after_signature.txt")));
+    Assertions.assertEquals("Checkpoint signature section must end with newline", ex.getMessage());
+  }
+
+  @Test
+  public void from_signatureFormatInvalid() throws Exception {
+    var ex =
+        Assertions.assertThrows(
+            RekorParseException.class,
+            () -> Checkpoints.from(getResource("error_signature_format_invalid.txt")));
+    Assertions.assertEquals(
+        "Checkpoint signature was invalid or improperly formatted", ex.getMessage());
+  }
+
+  @Test
+  public void from_signatureLengthInsufficient() throws Exception {
+    var ex =
+        Assertions.assertThrows(
+            RekorParseException.class,
+            () -> Checkpoints.from(getResource("error_signature_length_insufficient.txt")));
+    Assertions.assertEquals("Checkpoint signature contains too few bytes", ex.getMessage());
+  }
+}

sigstore-java/src/test/resources/dev/sigstore/samples/checkpoints/error_header_body_separator.txt

@@ -0,0 +1,5 @@
+rekor.sigstore.dev - 2605736670972794746
+37795272
+60ll7idWI1jYRZzxc+jKflYoW+4jWxgZaGR15ASsWt4=
+Timestamp: 1697034484441201852
+— rekor.sigstore.dev wNI9ajBGAiEAlWUH2HSPa6IMIRBgFcIXph3Mj9xM70WR0VVADvGIl/oCIQCgfvUUjR/X5jewlqpAWI8NuJIicKpTG64vo6UM5fpSgQ==

sigstore-java/src/test/resources/dev/sigstore/samples/checkpoints/error_header_count.txt

@@ -0,0 +1,4 @@
+rekor.sigstore.dev - 2605736670972794746
+37795272
+
+— rekor.sigstore.dev wNI9ajBGAiEAlWUH2HSPa6IMIRBgFcIXph3Mj9xM70WR0VVADvGIl/oCIQCgfvUUjR/X5jewlqpAWI8NuJIicKpTG64vo6UM5fpSgQ==

sigstore-java/src/test/resources/dev/sigstore/samples/checkpoints/error_no_newline_after_signature.txt

@@ -0,0 +1,6 @@
+rekor.sigstore.dev - 2605736670972794746
+37795272
+60ll7idWI1jYRZzxc+jKflYoW+4jWxgZaGR15ASsWt4=
+Timestamp: 1697034484441201852
+
+— rekor.sigstore.dev wNI9ajBGAiEAlWUH2HSPa6IMIRBgFcIXph3Mj9xM70WR0VVADvGIl/oCIQCgfvUUjR/X5jewlqpAWI8NuJIicKpTG64vo6UM5fpSgQ==

sigstore-java/src/test/resources/dev/sigstore/samples/checkpoints/error_no_signatures.txt

@@ -0,0 +1,5 @@
+rekor.sigstore.dev - 2605736670972794746
+37795272
+60ll7idWI1jYRZzxc+jKflYoW+4jWxgZaGR15ASsWt4=
+Timestamp: 1697034484441201852
+

sigstore-java/src/test/resources/dev/sigstore/samples/checkpoints/error_not_a_number.txt

@@ -0,0 +1,6 @@
+rekor.sigstore.dev - 2605736670972794746
+abcdefg
+60ll7idWI1jYRZzxc+jKflYoW+4jWxgZaGR15ASsWt4=
+Timestamp: 1697034484441201852
+
+— rekor.sigstore.dev wNI9ajBGAiEAlWUH2HSPa6IMIRBgFcIXph3Mj9xM70WR0VVADvGIl/oCIQCgfvUUjR/X5jewlqpAWI8NuJIicKpTG64vo6UM5fpSgQ==

sigstore-java/src/test/resources/dev/sigstore/samples/checkpoints/error_signature_format_invalid.txt

@@ -0,0 +1,6 @@
+rekor.sigstore.dev - 2605736670972794746
+37795272
+60ll7idWI1jYRZzxc+jKflYoW+4jWxgZaGR15ASsWt4=
+Timestamp: 1697034484441201852
+
+rekor.sigstore.dev wNI9ajBGAiEAlWUH2HSPa6IMIRBgFcIXph3Mj9xM70WR0VVADvGIl/oCIQCgfvUUjR/X5jewlqpAWI8NuJIicKpTG64vo6UM5fpSgQ==

sigstore-java/src/test/resources/dev/sigstore/samples/checkpoints/error_signature_length_insufficient.txt

@@ -0,0 +1,6 @@
+rekor.sigstore.dev - 2605736670972794746
+37795272
+60ll7idWI1jYRZzxc+jKflYoW+4jWxgZaGR15ASsWt4=
+Timestamp: 1697034484441201852
+
+— rekor.sigstore.dev wNI9aj

sigstore-java/src/test/resources/dev/sigstore/samples/checkpoints/valid.txt

@@ -0,0 +1,6 @@
+rekor.sigstore.dev - 2605736670972794746
+37795272
+60ll7idWI1jYRZzxc+jKflYoW+4jWxgZaGR15ASsWt4=
+Timestamp: 1697034484441201852
+
+— rekor.sigstore.dev wNI9ajBGAiEAlWUH2HSPa6IMIRBgFcIXph3Mj9xM70WR0VVADvGIl/oCIQCgfvUUjR/X5jewlqpAWI8NuJIicKpTG64vo6UM5fpSgQ==

sigstore-java/src/test/resources/dev/sigstore/samples/checkpoints/valid_multi_sig.txt

@@ -0,0 +1,7 @@
+rekor.sigstore.dev - 2605736670972794746
+37795272
+60ll7idWI1jYRZzxc+jKflYoW+4jWxgZaGR15ASsWt4=
+Timestamp: 1697034484441201852
+
+— rekor.sigstore.dev wNI9ajBGAiEAlWUH2HSPa6IMIRBgFcIXph3Mj9xM70WR0VVADvGIl/oCIQCgfvUUjR/X5jewlqpAWI8NuJIicKpTG64vo6UM5fpSgQ==
+— bob.loblaw.dev wNI9ajBGAiEAlWUH2HSPa6IMIRBgFcIRph3Mj9xM70WR0VVADvGIl/oCIQCgfvUUjR/X5jewlqpAWI8NuJIicKpTG64vo6UM5fpSgQ==