Minimal p2sh multisig signature checking example

Help
#1

Below I have created a minimal self-contained example of an error I am getting in my project, namely:

buffer.js:705
throw TypeError(‘value is out of bounds’);
^
TypeError: value is out of bounds
at TypeError ()
at checkInt (buffer.js:705:11)
at Buffer.writeUInt8 (buffer.js:715:5)
at BufferWriter.writeUInt8 (c:\Users\Sindre\Documents\GitHub\BitSwaprjs\node_modules\bitcore\lib\encoding\bufferwriter.js:42:7)
at Script.toBuffer (c:\Users\Sindre\Documents\GitHub\BitSwaprjs\node_modules\bitcore\lib\script\script.js:110:8)
at Interpreter.evaluate (c:\Users\Sindre\Documents\GitHub\BitSwaprjs\node_modules\bitcore\lib\script\interpreter.js:283:19)
at Interpreter.verify (c:\Users\Sindre\Documents\GitHub\BitSwaprjs\node_modules\bitcore\lib\script\interpreter.js:72:13)
at Object. (c:\Users\Sindre\Documents\GitHub\BitSwaprjs\test\plain.js:51:37)
at Module._compile (module.js:456:26)
at Object.Module._extensions…js (module.js:474:10)

In the example I am separately computing multisig signatures and checking their validity, which is important for my project

    // Create keys
    var sk1 = new PrivateKey();
    var sk2 = new PrivateKey();
    var sk3 = new PrivateKey();
    var pubkeys = [new PublicKey(sk1), new PublicKey(sk2)];

    // Build multisig redeem script which checks for 2 signatures matching 2 keys
    var redeemScript = Script.buildMultisigOut(pubkeys, 2, { noSorting : true });

    // Build p2sh output script based on this redeem script
    var scriptPubKey = Script.buildScriptHashOut(redeemScript);

    // Create spending transaction
    var tx = new Transaction();

    // FAKE outpoint funding tx
    tx.from(Transaction.UnspentOutput({
        txId: 'a0a08e397203df68392ee95b3f08b0b3b3e2401410a38d46ae0874f74846f2e9',
        outputIndex: 0,
        scriptPubKey: Script.empty(), // place holder
        satoshis: 20000000
    }));

    tx.to(new Address(new PublicKey(sk3), Networks.testnet), 20000000);

    // Create signatures
    var sig1 = sighash.sign(tx, sk1, crypto.Signature.SIGHASH_SINGLE, 0, scriptPubKey);
    var sig2 = sighash.sign(tx, sk2, crypto.Signature.SIGHASH_SINGLE, 0, scriptPubKey);

    // Create scriptSig
    var scriptSig = Script.buildP2SHMultisigIn(pubkeys, 2, [sig1, sig2], { noSorting : true, cachedMultisig : scriptPubKey });

    // Check signatures
    var flags = Script.Interpreter.SCRIPT_VERIFY_P2SH | Script.Interpreter.SCRIPT_VERIFY_STRICTENC;
    var validity = Script.Interpreter().verify(scriptSig, scriptPubKey, tx, 0, flags);
#2

I should say, I presumed that the validity of the utxo was not relevant, at any rate, I get the very same error with a valid utxo.

#3

Is there anything I can do to simplify this question so as to make it easier for someone to point me in the right direction?

#4

Hey Bedeho!

Sorry about the delay answering you.

The minimal way to verify these signatures I think would be:

var tx = Transaction().from({
        txId: 'a0a08e397203df68392ee95b3f08b0b3b3e2401410a38d46ae0874f74846f2e9',
        outputIndex: 0,
        scriptPubKey: "OP_DUP OP_HASH160 089acaba6af8b2b4fb4bed3b747ab1e4e60b4965 OP_EQUALVERIFY OP_CHECKSIG",
        satoshis: 20000000
    }, pubkeys, 2)
    .to(new Address(new PublicKey(sk3), Networks.testnet), 20000000);

// Create signatures
var sig1 = sighash.sign(tx, sk1, crypto.Signature.SIGHASH_SINGLE, 0, scriptPubKey);
var sig2 = sighash.sign(tx, sk2, crypto.Signature.SIGHASH_SINGLE, 0, scriptPubKey);

And then:

assert(tx. isValidSignature(sig1));
assert(tx. isValidSignature(sig2));
#5
  1. The given utxo scriptPubKey is not accepted:

bitcore\lib\script\script.js:154
Error: Invalid script: “OP_DUP OP_HASH160 089acaba6af8b2b4fb4bed3b747ab1e4e60b4965 OP_EQUALVERIFY OP_CHECKSIG”

Also, that is a standard P2PKH script, while we are really trying to spend a P2SH 2-2 multisig output script.

  1. This example does not actually set the variable “scriptPubKey” used for the signing.

Should this work?

var redeemScript = Script.buildMultisigOut(pubkeys, 2, { noSorting : true });
var scriptPubKey = Script.buildScriptHashOut(redeemScript);

  1. When I replace the scriptPubKey you provided with the one I specified in 2), then I get the following error

bitcore\lib\transaction\transaction.js:663
TypeError: Cannot read property ‘isValidSignature’ of undefined

#6

The problem in my initial example seems to be that Script.Interpreter().verify tries to evaluate the scriptSig I am providing, and the first step in this process is to call a toBuffer() on the script, which fails for some reason?

This is a minimal example replicating the error:

var sk = new PrivateKey();
var pubkeys = [new PublicKey(sk), new PublicKey(sk)];
var scriptSig = Script.buildP2SHMultisigIn(pubkeys, 2, [new Signature(), new Signature()]);
scriptSig.toBuffer();

#7

Turns out the problem was that buildP2SHMultisigIn() expects signatures as buffers, not Signature objects. When I fixed this the code no longer crashes, but instead says the signatures are not valid?

The code is now:

// Create keys
var sk1 = new PrivateKey();
var sk2 = new PrivateKey();

// Pubkey set
var pubkeys = [new PublicKey(sk1), new PublicKey(sk2)];

// Build multisig redeem script which checks for 2 signatures matching 2 keys
var redeemScript = Script.buildMultisigOut(pubkeys, 2, { noSorting : true });

// Build p2sh output script based on this redeem script
var scriptPubKey = Script.buildScriptHashOut(redeemScript);

// Transaction which spends p2sh output, but outpoint is FAKE.
var sk3 = new PrivateKey();
var tx = new Transaction().from({
txId: ‘a0a08e397203df68392ee95b3f08b0b3b3e2401410a38d46ae0874f74846f2e9’,
outputIndex: 0,
scriptPubKey: scriptPubKey,
satoshis: 20000
}).to(new Address(new PublicKey(sk3), Networks.testnet), 20000);

// Create signatures
var sigtype = bitcore.crypto.Signature.SIGHASH_SINGLE;

var sig1 = sighash.sign(tx, sk1, sigtype, 0, scriptPubKey);
var sig2 = sighash.sign(tx, sk2, sigtype, 0, scriptPubKey);

// HAVE TO ADD THIS DUE TO BUG WHERE ECDSA.SET() IGNORING nhashtype //
sig1.nhashtype = sigtype;
sig2.nhashtype = sigtype;

var sigBuffer1 = sig1.toTxFormat();
var sigBuffer2 = sig2.toTxFormat();

// Create scriptSig
var scriptSig = Script.buildP2SHMultisigIn(pubkeys, 2, [sigBuffer1, sigBuffer2], { noSorting : true});

// Check signatures
var flags = Script.Interpreter.SCRIPT_VERIFY_P2SH | Script.Interpreter.SCRIPT_VERIFY_STRICTENC;
var validity = Script.Interpreter().verify(scriptSig, scriptPubKey, tx, 0, flags);

console.log(validity);