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

Crypto and Bitcoin functions for Covenance DLC implementation

import { Transaction, Script, crypto } from '../btc';
import { Point } from '../crypto/secp256k1';
import { createAdaptorSig } from '../crypto/counterparty';
import { PrivKey, AdaptorSignature } from '../crypto/types';

export function sighashForAdaptorSig(
  transaction: Transaction,
  inputIndex: number,
  tapleafHash: Buffer
): Buffer {
  return Transaction.SighashSchnorr.sighash(
    transaction,
    crypto.Signature.SIGHASH_ALL | crypto.Signature.SIGHASH_ANYONECANPAY,
    inputIndex,
    crypto.Signature.Version.TAPSCRIPT,
    {
      annexPresent: false,
      annexInit: true,
      codeseparatorPosInit: true,
      codeseparatorPos: new crypto.BN(0xffffffff), // BIP-342: 0xffffffff means no codeseparator
      tapleafHashInit: true,
      tapleafHash
    }
  );
}

/**
 * Creates and applies an adaptor signature to a CET
 * @param cet - The CET transaction to sign
 * @param inputIndex - The index of the input to sign
 * @param privKey - The private key to sign with
 * @param oracleSigPoint - The oracle's signature point for the event outcome
 * @param tapleafHash - The hash of the tapleaf
 * @returns The adaptor signature
 */
export async function createCetAdaptorSig(
  cet: Transaction,
  inputIndex: number,
  privKey: PrivKey,
  oracleSigPoint: Point,
  tapleafHash: Buffer
): Promise<AdaptorSignature> {
  // Get the sighash of the CET
  const sighash = sighashForAdaptorSig(cet, inputIndex, tapleafHash);
  
  // Create the adaptor signature
  const adaptorSig = await createAdaptorSig(privKey, oracleSigPoint, sighash);
  
  return adaptorSig;
} 

/**
 * Creates a tapleaf hash for a given script
 * @param script - The script to create a tapleaf hash for
 * @param leafVersion - The version of the leaf
 * @returns The tapleaf hash
 */
export function tapleafHash(
  script: Script,
  leafVersion = 0xc0  // BIP-341
): Buffer {
  const scriptBuf = script.toBuffer();

  const tagWriter = crypto.TaggedHash.TAPLEAF;
  tagWriter.writeUInt8(leafVersion);
  tagWriter.writeVarintNum(scriptBuf.length);
  tagWriter.write(scriptBuf);

  return tagWriter.finalize();
}