Issue trying to sign offline P2PKH Transactions

[Alfonso Egio Artal]

Hello, I'm trying to build an offline transaction signer; full code here:

package org.bitcoinj.examples;

import org.bitcoinj.core.*;

import org.bitcoinj.crypto.TransactionSignature;

import org.bitcoinj.params.TestNet3Params;

import org.bitcoinj.script.Script;

import org.bitcoinj.script.ScriptBuilder;

import org.bitcoinj.script.ScriptOpCodes;

import javax.xml.bind.DatatypeConverter;

/**

 * SignTx on testnet ... does not work yet

 */

public class TxSigner {

    public static void main(String[] args) throws Exception {

        NetworkParameters params;

        params = TestNet3Params.get();

        // Initial data containing destination and unspent output address hashes

        String destinationPubKeyHash = "mrB5ZczDEMJtJ7xGXuD2tE2Qn4XX8RDRjX";

        String wif = "cRvcTPJtAxsYvn7Jnxw4BnymC7VfYF1HifVMh6uf7HbhsBXfyDqM";

        // Transaction containing the UTXO

        String originTxId = "8e213ee647d60de7bcb145cbf5f75527e892a459423b248c4ef610c2183b86b8";

        // Build the ECKey from the Wallet Interchange Format (wif) string

        DumpedPrivateKey dpk = DumpedPrivateKey.fromBase58(null, wif);

        ECKey key = dpk.getKey();

        String check = key.getPrivateKeyAsWiF(params);

        System.out.println(check);

        // Building addresses

        Address destinationAddress = Address.fromString(params, destinationPubKeyHash);

        // Initialize testnet transaction

        Transaction tx = new Transaction(params);

        // Add output spending the UTXO

        Long amount = new Long(8800000);

        tx.addOutput(Coin.valueOf(amount - 5000), destinationAddress);

        // Add some data in a second non-standard output

        String msg = "https://arxiv.org/abs/quant-ph/0012067";

        tx.addOutput(Coin.ZERO,

                ScriptBuilder.createOpReturnScript(msg.getBytes()));

        // Previous script

        ScriptBuilder redeemScriptBuilder = new ScriptBuilder();

        redeemScriptBuilder.op(ScriptOpCodes.OP_DUP)

                .op(ScriptOpCodes.OP_HASH160)

                .data(key.getPubKeyHash())

                .op(ScriptOpCodes.OP_EQUALVERIFY)

                .op(ScriptOpCodes.OP_CHECKSIG);

        Script redeemScript = redeemScriptBuilder.build();

        // Add originTxId as input with redeem script

        tx.addInput(Sha256Hash.wrap(originTxId),

                0,

                redeemScript);

        TransactionSignature txSignature = tx.calculateSignature(

                0,

                key,

                key.getPubKey(),

                Transaction.SigHash.ALL,

                false);

        Script scriptSig = new ScriptBuilder()

                .data(txSignature.encodeToBitcoin())

                .data(key.getPubKey())

                .build();

        assert (TransactionSignature.isEncodingCanonical(txSignature.encodeToBitcoin()));

        tx.getInput(0).setScriptSig(scriptSig);

        tx.verify();

        // Obtaining the hexadecimal raw transaction (does not validate)

        String tx_hex = DatatypeConverter.printHexBinary(tx.bitcoinSerialize());

        System.out.println(tx_hex);

    }

}

I was already achieving to properly validate a transaction like that built using BitcoinJS:

https://chain.so/tx/BTCTEST/8e213ee647d60de7bcb145cbf5f75527e892a459423b248c4ef610c2183b86b8

But not achieving it with previously posted Java code; main difference between both transactions is the signing script:

Correct signing script hex representation (generated with BitcoinJS):

483045022100ff8d4a710af05feaabdf313b38508985d899b7919bc3728e18e686ed8a8b2ab90220420876e4cb022716b2b523caa930d44e5baac59343f4c0b18805eb83f74b1f5801210384a4dcd4429e8fc5cf3f9f942e133b5b580022f89824e70515b0d2de21d435b7

Incorrect one hex representation (with previous code using bitcoinj):

47304402205ff33d777afbfcd40ff05a768781b87d10a6661ec723ac09bc4922e41ee7fba6022063b94f2169ca3e00aae3d753b6ebd1759dfe38b0bef6d24ee44cc575bee3fc4c03210384a4dcd4429e8fc5cf3f9f942e133b5b580022f89824e70515b0d2de21d435b7

It seems that the signature size is different by one byte (incorrect one 47, correct one 48).

Public Key Hex representation is:

0384a4dcd4429e8fc5cf3f9f942e133b5b580022f89824e70515b0d2de21d435b7

Can someone provide some hint/help about the issue or point me about what I'm doing wrong?

Many thanks in advance.