recoverPublicKey method

ECDSAPublicKey? recoverPublicKey(
  1. List<int> hash,
  2. ProjectiveECCPoint generator,
  3. int recId
)

Implementation

ECDSAPublicKey? recoverPublicKey(
    List<int> hash, ProjectiveECCPoint generator, int recId) {
  final curve = generator.curve;
  final order = generator.order!;
  final secret = BigintUtils.fromBytes(hash);
  final alpha =
      (r.modPow(BigInt.from(3), curve.p) + curve.a * r + curve.b) % curve.p;
  final beta = ECDSAUtils.modularSquareRootPrime(alpha, curve.p);
  BigInt y = (beta % BigInt.two == BigInt.zero) ? beta : (curve.p - beta);
  if (recId > 0) {
    y = -y;
  }
  final ProjectiveECCPoint r1 = ProjectiveECCPoint(
      curve: curve, x: r, y: y, z: BigInt.one, order: order);
  final ProjectiveECCPoint q1 = ((r1 * s) + (generator * (-secret % order))) *
      BigintUtils.inverseMod(r, order) as ProjectiveECCPoint;
  return ECDSAPublicKey(generator, q1);
}