Schnorr signer & Multisig Provider

[borislav-itskov]

Changes:

• You no longer need the private key to generate ephemeral nonces. The private key was used as a hashed key in the object but we removed it because it meant you need the private key just to exchange nonces which was inconvenient
• schnorr signer & multisig provider

Schnorr Signer

This PR introduces a schnorr signer that makes starting up pretty easily. It's main purpose is to hide the complexity behind it.
To initialize a signer, just create a new instance with your private key:

import { SchnorrSigner } from "@borislav.itskov/schnorrkel.js";

const privateKey = hexlify(randomBytes(32));
const signer = new SchnorrSigner(pk1);

And you're ready to go:

const msg = "test message";
const commitment = hashMessage(msg);
const signature = signer.sign(commitment);

This produces a verifiable signature again by the signer:

const result = signer.verify(commitment, signature);

On-chain, there's are two helper functions:

• signer.getSchnorrAddress() - which provides the schnorr ethereum address used for on-chain verifications
• signer.getEcrecoverSignature(signature) - which returns the on-chain data needed to successfully verify a signature

Schnorr Multisig Provider

The multisig provider cannot sign as it's not a signer. But he accepts a SchnorrSigner or it's parent class, SchnorrProvider, to help up with setting up the multisig:

const privateKeyHex = hexlify(randomBytes(32));
const publicKey = new Key(Buffer.from(arrayify(computePublicKey(privateKeyHex, true))));
const providerOne = new SchnorrProvider(publicKey);

const privateKeyHexTwo = hexlify(randomBytes(32));
const publicKeyTwo = new Key(Buffer.from(arrayify(computePublicKey(privateKeyHexTwo, true))));
const providerTwo = new SchnorrProvider(publicKeyTwo);

const multisigProvider = new SchnorrMultisigProvider([providerOne, providerTwo]);

OR if you have the signers, you can pass them:

const multisigProvider = new SchnorrMultisigProvider([signerOne, signerTwo]);

Once set up:

• you have getSchnorrAddress to give you directly the correct schnorr ethereum multisig address of all the signers
• getPublicNonces - which gets all the required public nonces from all the signers before signing can begin
• getEcrecoverSignature - a helper to format the on-chain data for the multisig