musig2

A simple and easy-to-use musig2 library, written in typescript.

Generates keys and nonce values for a group signing session.
Uses sign, combine and verify to create and validate signatures.
Simplified version of the latest musig2 protocol BIP0327.
Supports key tweaking for taproot script paths.

NOTE: This library is still under heavy development. Expect dragons!

Import

This package is available on NPM for easy import into your nodejs or browser-based project:

# Node via NPM:
npm install @cmdcode/musig2
# Node via Yarn:
yarn add @cmdcode/musig2

Example import as an ES module:

import * as Musig2 from '@cmdcode/musig2'

Example import into a browser-based project:

<script src="https://unpkg.com/@cmdcode/musig2"></script>
<script> const Musig2 = window.musig2 </script>

Basic Usage

Here is a basic example of using Musig2 for signing. The steps are as follows:

Each signer must collect the public keys and nonces from other signers.
Each signer then creates a session and partial signature.
Once all partial signatures are collected, any signer can combine them into the final signature.

Check out test/src/demo.test.ts for a full reference implementation.

// Import the package.
import * as Musig2 from '@cmdcode/musig2'

// Encode an example string as bytes.
const encoder = new TextEncoder()
const message = encoder.encode('Hello world!')

// Let's create an example list of signing members.
const members = [ 'alice', 'bob', 'carol' ]
// We'll store each member's keys in an array.
const wallets : any[] = []
// Let's also add some additional key tweaks.
const tweak1  = Musig2.gen.random()
const tweak2  = Musig2.gen.random()
const options = { tweaks : [ tweak1, tweak2 ] }

// Setup a dummy wallet for each signer.
for (const name of members) {
  // Generate some random secrets using WebCrypto.
  const secret = Musig2.gen.random(32)
  const nonce  = Musig2.gen.random(64)
  // Create a pair of signing keys.
  const [ sec_key, pub_key     ] = Musig2.gen.key_pair(secret)
  // Create a pair of nonce values (numbers only used once).
  const [ sec_nonce, pub_nonce ] = Musig2.gen.nonce_pair(nonce)
  // Add the member's wallet to the array.
  wallets.push({
    name, sec_key, pub_key, sec_nonce, pub_nonce
  })
}

// Collect public keys and nonces from all signers.
const group_keys   = wallets.map(e => e.pub_key)
const group_nonces = wallets.map(e => e.pub_nonce)

// Combine all your collected keys into a signing session.
const session = Musig2.combine.keys(group_keys, group_nonces, message, options)

// Each member creates their own partial signature,
// using their own computed signing session.
const group_sigs = wallets.map(wallet => {
  return Musig2.sign(
    session,
    wallet.sec_key,
    wallet.sec_nonce
  )
})

// Combine all the partial signatures into our final signature.
const signature = Musig2.combine.sigs(session, group_sigs)

// Check if the signature is valid.
const isValid1 = Musig2.verify.sig (
  session,
  signature
)

You can also verify the signature using an independent cryptography library, such as the excellent @noble/curves library by Paul Miller.

// BONUS: Check if the signature is valid using an independent library.
import { schnorr } from '@noble/curves/secp256k1'

const { group_pubkey } = session
const pubkey   = group_pubkey.slice(1)
const isValid2 = schnorr.verify(signature, message, pubkey)

Development / Testing

This library uses yarn for package management.

## Clean up any old builds.
yarn clean
## Run all tests in the suite.
yarn test
## Build a new release.
yarn release

Bugs / Issues

If you run into any bugs or have any questions, please submit an issue ticket.

Contribution

Feel free to fork and make contributions. Suggestions are welcome!

License

Use this library however you want!

Contact

You can find me on nostr at: npub1gg5uy8cpqx4u8wj9yvlpwm5ht757vudmrzn8y27lwunt5f2ytlusklulq3

Horus-Org/musig2