@covenance/dlc/src/cet/signature.ts

Crypto and Bitcoin functions for Covenance DLC implementation

import { Transaction } from '../btc';
import { Point } from '../crypto/secp256k1';
import { sighashForAdaptorSig } from './sighash';
import { createAdaptorSig, verifyAdaptorSig } from '../crypto/counterparty';
import { PrivKey, AdaptorSignature, Signature, PubKey } from '../crypto/types';
import { verifySig } from '../crypto/general';
import { be32 } from '../utils';

/**
 * Creates an adaptor signature for a CET
 * @param counterpartyPrivKey - The private key of the counterparty creating the signature
 * @param oracleSigPoint - The oracle's signature point for the event outcome
 * @param cet - The CET transaction to sign
 * @param inputIndex - The index of the input to sign in the CET
 * @param tapleafHash - The hash of the tapleaf
 * @returns The adaptor signature for the CET
 */
export async function signCetWithAdaptorSig(
  counterpartyPrivKey: PrivKey,
  oracleSigPoint: Point,
  cet: Transaction,
  inputIndex: number,
  tapleafHash: Buffer
): Promise<AdaptorSignature> {
  // Get the sighash for the CET
  const cetSighash = sighashForAdaptorSig(cet, inputIndex, tapleafHash);

  // Create the adaptor signature using the sighash as the message
  return createAdaptorSig(counterpartyPrivKey, oracleSigPoint, cetSighash);
}

/**
 * Verifies an adaptor signature for a CET
 * @param signature - The adaptor signature to verify
 * @param counterpartyPubKey - The counterparty's public key
 * @param oracleSigPoint - The oracle's signature point for the event outcome
 * @param cet - The CET transaction that was signed
 * @param inputIndex - The index of the input that was signed
 * @param tapleafHash - The hash of the tapleaf
 * @returns True if the signature is valid, false otherwise
 */
export async function verifyCetAdaptorSig(
  signature: AdaptorSignature,
  counterpartyPubKey: PubKey,
  oracleSigPoint: Point,
  cet: Transaction,
  inputIndex: number,
  tapleafHash: Buffer
): Promise<boolean> {
  // Get the sighash for the CET
  const cetSighash = sighashForAdaptorSig(cet, inputIndex, tapleafHash);
  
  // Verify the signature using the sighash as the message
  return verifyAdaptorSig(signature, counterpartyPubKey, cetSighash, oracleSigPoint);
}

/**
 * Verifies a completed signature for a CET
 * @param signature - The completed signature to verify
 * @param counterpartyPubKey - The counterparty's public key
 * @param cet - The CET transaction that was signed
 * @param inputIndex - The index of the input that was signed
 * @param tapleafHash - The hash of the tapleaf
 * @returns True if the signature is valid, false otherwise
 */
export async function verifyCetSignature(
  signature: Signature,
  counterpartyPubKey: PubKey,
  cet: Transaction,
  inputIndex: number,
  tapleafHash: Buffer
): Promise<boolean> {
  // Get the sighash for the CET
  const cetSighash = sighashForAdaptorSig(cet, inputIndex, tapleafHash);
  
  // Verify the signature using the sighash as the message
  return verifySig(signature, counterpartyPubKey, cetSighash);
} 

/**
 * Taproot/SegWit-v1 Schnorr signature serializer
 * @param signature - The signature to serialize
 * @param sighash - The sighash to serialize
 * @returns The serialized signature
 */
export function sigToTaprootBuf(
  { R, s }: Signature,
  sighash = 0x00
): Uint8Array {
  const addFlag = sighash !== 0x00;
  const out = new Uint8Array(addFlag ? 65 : 64);

  be32(out, 0,  R.x);
  be32(out, 32, s);
  if (addFlag) out[64] = sighash;

  return out;
}