isValidEip191Signature static method

bool isValidEip191Signature(String address, String message, String sig)

Implementation

static bool isValidEip191Signature(
  String address,
  String message,
  String sig,
) {
  // Get the sig bytes
  final sigBytes = Uint8List.fromList(
    hex.decode(
      sig.substring(2),
    ),
  );

  // Get the r and s values from the sig bytes
  final r = BigInt.parse(
    hex.encode(
      sigBytes.sublist(0, 32),
    ),
    radix: 16,
  );
  late BigInt s;
  late int v;

  // Depending on the length of the sig bytes, we can determine the v value
  if (sigBytes.length == 64) {
    Uint8List sBytes = sigBytes.sublist(32, 64);
    sBytes[0] &= 0x7f;
    v = (sBytes[0] & 0x80 == 0) ? 27 : 28;
    s = BigInt.parse(hex.encode(sBytes), radix: 16);
  } else {
    Uint8List sBytes = sigBytes.sublist(32, 64);
    v = getNormalizedV(sigBytes[64]);
    s = BigInt.parse(hex.encode(sBytes), radix: 16);
  }

  // Recover the public key from the signature
  Uint8List? publicKeyBytes = AuthSecp256k1.recoverPublicKeyFromSignature(
    v - 27,
    r,
    s,
    hashMessage(message),
  );

  // If the public key is null, return false
  if (publicKeyBytes == null) {
    return false;
  }

  // Convert the public key to an address
  final hashedPubKeyBytes = keccak256(publicKeyBytes);
  final addressBytes = hashedPubKeyBytes.sublist(12, 32);
  final recoveredAddress = '0x${hex.encode(addressBytes)}';

  return recoveredAddress.toLowerCase() == address.toLowerCase();
}