Add logic to extractWitnessCommitmentHash in the Bridge

rskj-core/src/main/java/co/rsk/peg/bitcoin/BitcoinUtils.java

@@ -12,9 +12,9 @@
 import org.slf4j.LoggerFactory;
 
 public class BitcoinUtils {
-    public static final byte WITNESS_COMMITMENT_LENGTH = 36; // 4 bytes for header, 32 for hash
-    public static final Sha256Hash WITNESS_RESERVED_VALUE = Sha256Hash.ZERO_HASH;
     protected static final byte[]  WITNESS_COMMITMENT_HEADER = Hex.decode("aa21a9ed");
+    protected static final int WITNESS_COMMITMENT_LENGTH = WITNESS_COMMITMENT_HEADER.length + Sha256Hash.LENGTH;
+    private static final int MINIMUM_WITNESS_COMMITMENT_SIZE = WITNESS_COMMITMENT_LENGTH + 2; // 1 extra by for OP_RETURN and another one for data length
     private static final Logger logger = LoggerFactory.getLogger(BitcoinUtils.class);
     private static final int FIRST_INPUT_INDEX = 0;
 
@@ -90,7 +90,7 @@ public static Optional<Sha256Hash> findWitnessCommitment(BtcTransaction tx) {
         for (TransactionOutput output : outputsReversed) {
             Script scriptPubKey = output.getScriptPubKey();
             if (isWitnessCommitment(scriptPubKey)) {
-                Sha256Hash witnessCommitment = ScriptPattern.extractWitnessCommitmentHash(scriptPubKey);
+                Sha256Hash witnessCommitment = extractWitnessCommitmentHash(scriptPubKey);
                 return Optional.of(witnessCommitment);
             }
         }
@@ -99,7 +99,6 @@ public static Optional<Sha256Hash> findWitnessCommitment(BtcTransaction tx) {
     }
 
     private static boolean isWitnessCommitment(Script scriptPubKey) {
-        final int MINIMUM_WITNESS_COMMITMENT_SIZE = 38;
         byte[] scriptPubKeyProgram = scriptPubKey.getProgram();
 
         return scriptPubKeyProgram.length >= MINIMUM_WITNESS_COMMITMENT_SIZE
@@ -115,4 +114,21 @@ private static boolean hasCommitmentStructure(byte[] scriptPubKeyProgram) {
     private static boolean hasWitnessCommitmentHeader(byte[] header) {
         return Arrays.equals(header, WITNESS_COMMITMENT_HEADER);
     }
+
+    /**
+     * Retrieves the hash from a segwit commitment (in an output of the coinbase transaction).
+     */
+    private static Sha256Hash extractWitnessCommitmentHash(Script scriptPubKey) {
+        byte[] scriptPubKeyProgram = scriptPubKey.getProgram();
+        Preconditions.checkState(scriptPubKeyProgram.length >= MINIMUM_WITNESS_COMMITMENT_SIZE);
+
+        final int WITNESS_COMMITMENT_HASH_START = 6; // 4 bytes for header + OP_RETURN + data length
+        byte[] witnessCommitmentHash = Arrays.copyOfRange(
+            scriptPubKeyProgram,
+            WITNESS_COMMITMENT_HASH_START,
+            MINIMUM_WITNESS_COMMITMENT_SIZE
+        );
+
+        return Sha256Hash.wrap(witnessCommitmentHash);
+    }
 }

rskj-core/src/test/java/co/rsk/peg/bitcoin/BitcoinTestUtils.java

@@ -14,6 +14,7 @@
 import org.ethereum.util.ByteUtil;
 
 public class BitcoinTestUtils {
+    public static final Sha256Hash WITNESS_RESERVED_VALUE = Sha256Hash.ZERO_HASH;
 
     public static BtcECKey getBtcEcKeyFromSeed(String seed) {
         byte[] serializedSeed = HashUtil.keccak256(seed.getBytes(StandardCharsets.UTF_8));
@@ -215,7 +216,7 @@ public static BtcTransaction createCoinbaseTransactionWithWrongWitnessCommitment
         byte[] wrongWitnessCommitmentWithHeader = ByteUtil.merge(
             new byte[]{ScriptOpCodes.OP_RETURN},
             new byte[]{ScriptOpCodes.OP_PUSHDATA1},
-            new byte[]{BitcoinUtils.WITNESS_COMMITMENT_LENGTH},
+            new byte[]{(byte) BitcoinUtils.WITNESS_COMMITMENT_LENGTH},
             BitcoinUtils.WITNESS_COMMITMENT_HEADER,
             witnessCommitment.getBytes()
         );
@@ -230,7 +231,7 @@ private static BtcTransaction createCoinbaseTxWithWitnessReservedValue(NetworkPa
         BtcTransaction coinbaseTx = createCoinbaseTransaction(networkParameters);
 
         TransactionWitness txWitness = new TransactionWitness(1);
-        txWitness.setPush(0, BitcoinUtils.WITNESS_RESERVED_VALUE.getBytes());
+        txWitness.setPush(0, WITNESS_RESERVED_VALUE.getBytes());
         coinbaseTx.setWitness(0, txWitness);
 
         return coinbaseTx;

rskj-core/src/test/java/co/rsk/peg/bitcoin/BitcoinUtilsTest.java

@@ -33,7 +33,7 @@ private boolean isSigHashValid(Sha256Hash sigHash, List<BtcECKey> pubKeys, List<
         LinkedList<BtcECKey> keys = new LinkedList<>(pubKeys);
         LinkedList<BtcECKey.ECDSASignature> sigs = new LinkedList<>(signatures);
 
-        while (sigs.size() > 0){
+        while (!sigs.isEmpty()){
             BtcECKey pubKey = keys.pollFirst();
             BtcECKey.ECDSASignature signature = sigs.getFirst();
             if(pubKey.verify(sigHash, signature)){
@@ -272,7 +272,7 @@ void extractRedeemScriptFromInput_p2sh_pegin_v1() {
         assertFalse(btcTx.getInputs().isEmpty());
 
         List<ScriptChunk> scriptSigChunks = scriptSig.getChunks();
-        Script expectedRedeemScript = new Script( scriptSigChunks.get(scriptSigChunks.size()- 1).data);
+        Script expectedRedeemScript = new Script(scriptSigChunks.get(scriptSigChunks.size()- 1).data);
 
         // Act
         Optional<Script> redeemScript = BitcoinUtils.extractRedeemScriptFromInput(btcTx.getInputs().get(FIRST_INPUT_INDEX));
@@ -512,7 +512,7 @@ void findWitnessCommitment_withDataLargenThanExpected_shouldReturnEmpty() {
         BtcTransaction btcTx = BitcoinTestUtils.createCoinbaseTransaction(btcMainnetParams);
 
         TransactionWitness txWitness = new TransactionWitness(1);
-        txWitness.setPush(0, BitcoinUtils.WITNESS_RESERVED_VALUE.getBytes());
+        txWitness.setPush(0, BitcoinTestUtils.WITNESS_RESERVED_VALUE.getBytes());
         btcTx.setWitness(0, txWitness);
 
         Sha256Hash witnessCommitment = BitcoinTestUtils.createHash(100);