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.


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