Multi-signature Native Segwit 2 of 4

To follow along this tutorial

Clone the Github repository
cd code
npm install or yarn install
Execute the transaction code by typing node tx_filename.js
Alternatively you can enter the commands step-by-step by cd into ./code then type node in a terminal to open the Node.js REPL
Open the Bitcoin Core GUI console or use bitcoin-cli for the Bitcoin Core commands
Use bx aka Libbitcoin-explorer as a handy complement

Let’s create a 2 of 4 multi-signature with a native Segwit P2WSH transaction.

Creating and Funding the P2WSH

Import libraries, test wallets and set the network

const bitcoin = require('bitcoinjs-lib')
const { alice, bob, carol, dave } = require('./wallets.json')
const network = bitcoin.networks.regtest

Prepare four keypairs.

const keyPairAlice1 = bitcoin.ECPair.fromWIF(alice[1].wif, network)
const keyPairBob1 = bitcoin.ECPair.fromWIF(bob[1].wif, network)
const keyPairCarol1 = bitcoin.ECPair.fromWIF(carol[1].wif, network)
const keyPairDave1 = bitcoin.ECPair.fromWIF(dave[1].wif, network)

And an other alice_2 that will redeem the multi-signature funds.

const keyPairAlice2 = bitcoin.ECPair.fromWIF(alice[2].wif, network)
const p2wpkhAlice2 = bitcoin.payments.p2wpkh({pubkey: keyPairAlice2.publicKey, network})

Create the locking script with the special p2ms payment method.

const p2ms = bitcoin.payments.p2ms({
  m: 2, pubkeys: [
    keyPairAlice1.publicKey,
    keyPairBob1.publicKey,
    keyPairCarol1.publicKey,
    keyPairDave1.publicKey], network})

console.log('Script:')
console.log(p2ms.output.toString('hex'))

Check the locking script.

decodescript SCRIPT

02 03745c9aceb84dcdeddf2c3cdc1edb0b0b5af2f9bf85612d73fa6394758eaee35d 027efbabf425077cdbceb73f6681c7ebe2ade74a65ea57ebcf0c42364d3822c590
023a11cfcedb993ff2e7523f92e359c4454072a66d42e8b74b4b27a8a1258abddd 02e9d617f38f8c3ab9a6bde36ce991bafb295d7adba457699f8620c8160ec9e87a 04
OP_CHECKMULTISIG

Feed the p2wsh method with the special BitcoinJS p2ms object.

const p2wsh = bitcoin.payments.p2wsh({redeem: p2ms, network})
console.log('P2WSH address')
console.log(p2wsh.address) (1)

1	The `p2wsh` method generates an object that contains the P2WSH address.

Send 1 BTC to this P2WSH address.

sendtoaddress bcrt1qtvraes6lc2efmwqtupv7f9wg3adhvzwpu0vg3s2zgpnc7qpp0v7sj6dkmu 1

Get the output index so that we have the outpoint (txid / vout).

gettransaction TX_ID

Find the output index (or vout) under vout.

Preparing the spending transaction

Now let’s prepare the spending transaction by setting input and output and having two persons (private keys) to sign the transaction. Here alice_1 and bob_1 will redeem the P2WSH multi-signature and send the funds to alice_2 P2WPKH address.

Create a BitcoinJS transaction builder object.

const txb = new bitcoin.TransactionBuilder(network)

Create the input by referencing the outpoint of our P2WSH funding transaction.

txb.addInput('TX_ID', TX_VOUT)

Create the output that will send the funds to alice_2 P2WPKH address, leaving 100 000 satoshis as mining fees.

txb.addOutput(p2wpkhAlice2.address, 999e5)

Alice_1 and bob_1 now sign the transaction.

// txb.sign(index, keyPair, redeemScript, sign.hashType, value, witnessScript)
txb.sign(0, keyPairAlice1, null, null, 1e8, p2wsh.redeem.output)
txb.sign(0, keyPairBob1, null, null, 1e8, p2wsh.redeem.output)

Note that, because we are doing a P2WSH, we need to provide the locking script as witnessScript sixth parameter of the sign method, as well as the previous output value.

Build the transaction and get the raw hex serialization.

const tx = txb.build()
console.log('Transaction hexadecimal:')
console.log(tx.toHex())

Inspect the raw transaction with Bitcoin Core CLI, check that everything is correct.

decoderawtransaction TX_HEX

Broadcasting the transaction

It’s time to broadcast the transaction via Bitcoin Core CLI.

sendrawtransaction TX_HEX

Inspect the transaction.

getrawtransaction TX_ID true

Observations

We can see that the scriptSig unlocking script is empty. Instead all the data are located in the txinwitness field and contains:

An empty string that will convert to a dummy but mandatory 00 value due to a bug in OP_CHECKMULTISIG
Alice_1 and bob_1 signatures
The witness script

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