Unchained Capital Bitcoin Utilities

This library builds on the excellent bitcoinjs-lib, adding valuable but missing functionality for validation, HD wallets, block explorers, and especially multisig.

Full API documentation can be found at unchained-bitcoin.

This library was built and is maintained by Unchained Capital.

Installation

unchained-bitcoin is distributed as an NPM package. Add it to your application's dependencies:

$ npm install --save unchained-bitcoin

Usage

The library provides a functional API which builds upon data structures used by bitcoinjs-lib.

In particular, many functions accept a Multisig object which is the type name given by this library to the kind of object returned by functions such as bitcoin.payments.p2ms, bitcoin.payments.p2sh, &c. from bitcoinjs-lib.

The examples below provide an initial idea of how to use this library, but see the API documentation for full details.

Interacting with a multisig address.

Generating multisigs

Multisig objects can be generated with two functions:

generateMultisigFromPublicKeys -- useful when directly passing public keys
generateMultisigFromHex -- useful when parsing an existing redeem/witness script

Each of these functions accepts additional arguments which determines the multisig address type (e.g. P2SH or P2WSH).

import {
	generateMultisigFromPublicKeys,
	generateMultisigFromHex,
	P2SH,                      // or: P2SH_P2WSH, P2WSH,
	TESTNET,                   // or: MAINNET,
	multisigAddress,
} from "unchained-bitcoin";

// Public keys are represented as compressed hex.
const publicKeys = [
  "02a8513d9931896d5d3afc8063148db75d8851fd1fc41b1098ba2a6a766db563d4",
  "03938dd09bf3dd29ddf41f264858accfa40b330c98e0ed27caf77734fac00139ba",
];

// A testnet P2SH 2-of-2 multisig.
const m1 = generateMultisigFromPublicKeys(TESTNET, P2SH, 2, ...publicKeys);
console.log(multisigAddress(m1))
// 2N5KgAnFFpmk5TRMiCicRZDQS8FFNCKqKf1

const redeemScript = "522102a8513d9931896d5d3afc8063148db75d8851fd1fc41b1098ba2a6a766db563d42103938dd09bf3dd29ddf41f264858accfa40b330c98e0ed27caf77734fac00139ba52ae";
// Same as m1 but using redeem script
const m2 = generateMultisigFromHex(TESTNET, P2SH, redeemScript);
console.log(multisigAddress(m2))
// 2N5KgAnFFpmk5TRMiCicRZDQS8FFNCKqKf1

Querying multisigs

Multisig objects can be passed around and queried with other functions in the API.


multisigAddress(multisig); // Returns public address
multisigAddressType(multisig); // P2SH
multisigRequiredSigners(multisig); // 2
multisigTotalSigners(multisig); // 3
multisigScript(multisig); // Returns redeem OR witness script, as appropriate
multisigRedeemScript(multisig); // Returns redeem script in hex (null for P2WSH)
multisigWitnessScript(multisig); // Returns witness script in hex (null for P2SH)
multisigPublicKeys(multisig); // Returns publicKeys

See the API documentation for full details on these functions.

Multisig Transactions

Multisig objects can be used to draft signed or unsigned transactions and to validate transaction signatures.

import {
  generateMultisigFromPublicKeys, TESTNET, P2SH,
  unsignedMultisigTransaction,
  validateMultisigSignature,
} from "unchained-bitcoin";
// Spending 3 UTXOs from the same multisig address.

// First build the multisig for the address.
const publicKeys = ["02a8513d9931896d5d3afc8063148db75d8851fd1fc41b1098ba2a6a766db563d4", "03938dd09bf3dd29ddf41f264858accfa40b330c98e0ed27caf77734fac00139ba"];
const multisig = generateMultisigFromPublicKeys(TESTNET, P2SH, 2, ...publicKeys);

// All 3 UTXOs are at the same address so get decorated with the same multisig object.
const inputs = [
  {
    txid: "65e7ef764030dabfb46e3ae1c357b0666d0dda722c9809fb73245d6d68665284",
    index: 1,
	multisig,
  },
  {
    txid: "ae9e1aa8312e102e806fa11d8e65965a624f88459e6bb5bcf48156a0c53e022a",
    index: 1,
	multisig,
  },
  {
    txid: "f243c1fbb85dd49da91477b89c76636202721be9c7df5ee6eee0c6a10861ae44",
    index: 0,
	multisig,
  }
];

const outputs = [
  {
    address: "2NE1LH35XT4YrdnEebk5oKMmRpGiYcUvpNR",
    amountSats: 291590,
  }
];


const unsignedTransaction = unsignedMultisigTransaction(TESTNET, inputs, outputs);

// Pass the above unsigned transaction to some keystore device/software to obtain a signature.
//
// One signature value per input.
const transactionSignature1 = [
  "304402205397795a8b6e0b8d1c5a0b2b5b8fb8e49afb6dd150d1a186604fa9e71e23aaa20220514b7b7ed9ec43d983d7be5ea4ece5a55b29efa2193d90bf1fd087356fcbd54b",
  "304402200ffcb2331655f1f24bf2f7e16984d81310e55d47c405b45e327abde524c8d31e022036460b70a665d1756ea91e131a1ed1022544dfdd2232f64117230d22f9deeb08",
  "30440220167a35bccf4bb13073e8c66a1b094906d5c7879d6cdac730e435aef196d2f3eb02205a39e05763e511dc15deff56fa29eead850623076fda8a5e173dd0942197aaf4"
];

// Signatures can be validated.
transactionSignature1.forEach((inputSignature, inputIndex) => {
  const result = validateMultisigSignature(unsignedTransaction, inputIndex, inputs[inputIndex], inputSignature);
  if (!result) {
    console.error(`Invalid signature for input ${inputIndex + 1}`);
  }
})

// Get the second required signature.
const transactionSignature2 = [
  "304a...",
  "304b...",
  "304c...",
];

// Combine signatures into a fully signed transaction.
const signedTransaction = signedMultisigTransaction(TESTNET, inputs, outputs, transactionSignature1, transactionSignature2);

// Broadcast this transaction somehow...
console.log(signedTransaction.tHex());

Validation

This library contains several useful functions for validation not provided by bitcoinjs-lib or other libraries. The validation functions are designed to return an empty string '' on valid input and provide a helpful error message otherwise.

validateAddress -- understands Bech32 addresses and is aware of differences in addresses across networks
valdiateBIP32Path -- understands absolute and relative BIP32 paths, validates maximum BIP32 index values, and can optionally check for fully hardened or unhardened paths
validateExtendedPublicKey -- understands network-dependent differences in encoding extended public keys
validatePublicKey -- allows any hexadecimal value
validateFeeRate -- implements a reasonable maximum fee rate in Satoshis/byte
validateFee -- implements a reasonable maximum fee in BTC
validateOutputAmount -- checks for dust and that amount is less than total input amount
validateMultisigSignature -- checks signatures for correctness and works across all multisig address types

Developers

Developers who want to work on this library should clone the source code and install dependencies:

$ git clone https://github.com/unchained-capital/unchained-bitcoin`
...
$ cd unchained-bitcoin
$ npm install

Testing

Unit tests are implemented in Jest and can be run via

$ npm test

Contributing

Unchained Capital welcomes bug reports, new features, and better documentation for this library.

If you are fixing a bug or adding a feature, please first check the GitHub issues page to see if there is any existing discussion about it.

To contribute, create a pull request (PR) on GitHub against the Unchained Capital fork of unchained-bitcoin.

Before you submit your PR, make sure to update and run the test suite!

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