generateNonce function

String generateNonce(PublicKey publicKey, int maxEpoch, dynamic randomness)

Generates the zkLogin nonce that commits to the ephemeral publicKey, the maxEpoch until which it is valid, and a randomness value.

randomness may be either a decimal String (as returned by generateRandomness) or a BigInt; any other type throws an ArgumentError. Throws an Exception if the derived nonce is not NONCE_LENGTH characters long.

Implementation

String generateNonce(PublicKey publicKey, int maxEpoch, dynamic randomness) {
  final publicKeyBytes = toBigIntBE(publicKey.toSuiBytes());
  final ephPublicKey0 = publicKeyBytes ~/ BigInt.two.pow(128);
  final ephPublicKey1 = publicKeyBytes % BigInt.two.pow(128);
  BigInt bigNum;

  if (randomness is String) {
    bigNum = poseidonHash([
      ephPublicKey0,
      ephPublicKey1,
      BigInt.from(maxEpoch),
      BigInt.parse(randomness),
    ]);
  } else if (randomness is BigInt) {
    bigNum = poseidonHash([
      ephPublicKey0,
      ephPublicKey1,
      BigInt.from(maxEpoch),
      randomness,
    ]);
  } else {
    throw ArgumentError(
      'Invalid type for randomness. It should be either BigInt or String.',
    );
  }

  final z = toBigEndianBytes(bigNum, 20);
  final nonce = base64UrlEncode(
    z,
  ).replaceAll('=', '').replaceAll('+', '-').replaceAll('/', '_');
  if (nonce.length != NONCE_LENGTH) {
    throw Exception(
      'Length of nonce $nonce (${nonce.length}) is not equal to $NONCE_LENGTH',
    );
  }
  return nonce;
}