sign method

ECDSASignature sign(BigInt hash, BigInt randomK)

Signs a hash value using the private key.

Parameters:

• hash: A hash value of the message to be signed.
• randomK: A random value for signature generation.

Returns: An ECDSA signature.

Implementation

ECDSASignature sign(BigInt hash, BigInt randomK) {
  final BigInt? n = publicKey.generator.order;
  if (n == null) {
    throw ArgumentException.invalidOperationArguments(
      "sign",
      reason: "Invalid curve generator.",
    );
  }

  final BigInt k = randomK % n;
  final BigInt ks = k + n;
  final BigInt kt = ks + n;

  BigInt r;
  if (ks.bitLength == n.bitLength) {
    r = (publicKey.generator * kt).x % n;
  } else {
    r = (publicKey.generator * ks).x % n;
  }

  if (r == BigInt.zero) {
    throw const CryptoSignException(
      "ECDSA signing aborted. nonce generation failed.",
    );
  }

  final BigInt s =
      (BigintUtils.inverseMod(k, n) * (hash + (secretMultiplier * r) % n)) %
      n;

  if (s == BigInt.zero) {
    throw const CryptoSignException(
      "ECDSA signing aborted. s generation failed.",
    );
  }

  return ECDSASignature(r, s);
}