Bitcoinjs-lib: Signing a custom P2SH multisig

[rbndg]

Hello everybody.

I'm trying to sign a custom P2SH Multisig but i'm having trouble.
From my understanding the "sign" method in TransactionBuilder only accepts a set of standard transactions.

This is my attempt:

    var keyPairs = [
      "cRmbQiGDNF7FGNuY7PeTS2VTG59s2kHUjVEf65dtFRWV2CJKnkzK",
      "cSwigfrwCHr2npxtRhQGUyg87uThQTjscWx6twmYSSzkZT2rB7GC"
    ].map(function(wif) {
      return bitcoin.ECPair.fromWIF(wif, testnet);
    });
    var pubKeys = keyPairs.map(function(x) {
      return x.getPublicKeyBuffer();
    });

  // 2-2 Multi-sig with an IF statement
    var witnessScript = bitcoin.script.compile(
      [].concat(ops.IF, ops.OP_RESERVED + 2, pubKeys, ops.OP_RESERVED + 2, ops.OP_CHECKMULTISIG, ops.ENDIF)
    );  

    var witnessScriptHash = bitcoin.crypto.sha256(witnessScript);
    var redeemScript = bitcoin.script.witnessScriptHash.output.encode(witnessScriptHash);
    var redeemScriptHash = bitcoin.crypto.hash160(redeemScript);
    var scriptPubKey = bitcoin.script.scriptHash.output.encode(redeemScriptHash);
    var address = bitcoin.address.fromOutputScript(scriptPubKey, bitcoin.networks.testnet);

    testnetUtils.faucet(address, 6e4, function(err, unspent) {
      if (err) return done(err);

      var txb = new bitcoin.TransactionBuilder(testnet);
      txb.addInput(unspent.txId, unspent.vout);
      txb.addOutput(testnetUtils.RETURN_ADDRESS, 4e4);
      txb.sign(0, keyPairs[0], redeemScript, null, unspent.value, scriptPubKey);
      txb.sign(0, keyPairs[1], redeemScript, null, unspent.value, scriptPubKey);

// The redeem script should be:
//  <sig 1, sig2> 1
// However im unsure on how to do this :(

      var tx = txb.build();

      // build and broadcast to the Bitcoin Testnet network
      testnetUtils.transactions.propagate(tx.toHex(), function(err) {
        if (err) return done(err);

        testnetUtils.verify(address, tx.getId(), 4e4, done);
      });
    });

Thanks for your help

[dabura667]

TransactionBuilder only supports specific transaction types.

If you'd like to know how to sign, look at the sign function, and create a similar function within your app.

[rbndg]

Thanks for you help :)
I'm using the Transaction class to create a raw transaction.

When I broadcast the transaction I get the following error:
Error: 64: non-mandatory-script-verify-flag (Signature must be zero for failed CHECK(MULTI)SIG operation)
I believe i'm not generating the sig correctly?

      var txb = new bitcoin.Transaction();
      txb.ins.push({
        hash: Buffer.from(unspent.txId, "hex").reverse(),
        index: 0,
        script: bitcoin.script.compile([redeemScript]), 
        sequence: 0xffffffff
      });
      const hash = txb.hashForWitnessV0(0, witnessScript, unspent.value, bitcoin.Transaction.SIGHASH_ALL);

      const sig1 = keyPairs[0].sign(hash).toScriptSignature(bitcoin.Transaction.SIGHASH_ALL);
      const sig2 = keyPairs[1].sign(hash).toScriptSignature(bitcoin.Transaction.SIGHASH_ALL);
      const witness = [sig2, sig1, Buffer.from("01", "hex"), witnessScript];
      txb.ins[0].witness = witness;

      txb.outs.push({
        script: scriptPubKey, 
        value: 4e4
      });

txb.toHex()

[dabura667]

you can't add an output after generating the sighash...

[dabura667]

Also, be sure that the sig order is correct. Otherwise it will fail.

[afk11]

looks like the null byte for the CHECKMULTISIG is missing also?

[afk11]

Got the following to work, slightly modified the script into an IF/ELSE.

var bitcoin = require('./src/index.js')
var bcrypto = bitcoin.crypto;
var bscript = bitcoin.script;
var ops = require('bitcoin-ops');

var testnet = bitcoin.networks.testnet;

var keyPairs = [
  "cRmbQiGDNF7FGNuY7PeTS2VTG59s2kHUjVEf65dtFRWV2CJKnkzK",
  "cSwigfrwCHr2npxtRhQGUyg87uThQTjscWx6twmYSSzkZT2rB7GC"
].map(function(wif) {
  return bitcoin.ECPair.fromWIF(wif, testnet);
});
var pubKeys = keyPairs.map(function(x) {
  return x.getPublicKeyBuffer();
});

// if 2-of-2-multisig else [alice
var scriptParts = [].concat(
  ops.OP_IF, 
    ops.OP_2, pubKeys[0], pubKeys[1], ops.OP_2, ops.OP_CHECKMULTISIG, 
  ops.OP_ELSE, 
    pubKeys[1], ops.OP_CHECKSIG, 
  ops.OP_ENDIF);

var witnessScript = bitcoin.script.compile(
  scriptParts
);
console.log(bscript.toASM(scriptParts))

var witnessHash = bcrypto.sha256(witnessScript)
var redeemScript = bscript.witnessScriptHash.output.encode(witnessHash)
var redeemScript160 = bcrypto.hash160(redeemScript)

var value = 100000000
var scriptPubKey = bscript.scriptHash.output.encode(redeemScript160)
var txId = "abcd1234abcd1234abcd1234abcd1234abcd1234abcd1234abcd1234abcd1234";
var vout = 0

var txb = new bitcoin.Transaction();
txb.ins.push({
  hash: Buffer.from(txId, "hex").reverse(),
  index: vout,
  script: bitcoin.script.compile([redeemScript]),
  sequence: 0xffffffff
});

txb.outs.push({
  script: scriptPubKey,
  value: 90000000
});

var hash = txb.hashForWitnessV0(0, witnessScript, value, bitcoin.Transaction.SIGHASH_ALL);
var sig1 = keyPairs[0].sign(hash).toScriptSignature(bitcoin.Transaction.SIGHASH_ALL);
var sig2 = keyPairs[1].sign(hash).toScriptSignature(bitcoin.Transaction.SIGHASH_ALL);

var witness1 = [Buffer.from("", "hex"), sig1, sig2, Buffer.from("01", "hex"), witnessScript];
txb.ins[0].witness = witness1;

var hex = txb.toHex()
console.log(hex)

var witness2 = [sig2, Buffer.from("", "hex"), witnessScript];
txb.ins[0].witness = witness2;

var hex = txb.toHex()
console.log(hex)

[rbndg]

Thank you so much that worked perfectly:
Hopefully I can start contributing soon. :)