deriveKey method

@override Future<SecretKey> deriveKey({ required SecretKey secretKey, required List<int> nonce, })

Generates a new secret key from a secret key and a nonce.

Implementation

@override
Future<SecretKey> deriveKey({
  required SecretKey secretKey,
  required List<int> nonce,
}) async {
  final numberOfBytes = (bits + 7) ~/ 8;
  final macLength = macAlgorithm.macLength;
  final result = Uint8List(
    ((numberOfBytes + macLength - 1) ~/ macLength) * macLength,
  );

  // Subsequent blocks
  final firstInput = Uint8List(nonce.length + 4);
  firstInput.setAll(0, nonce);
  for (var i = 0; i < result.lengthInBytes ~/ macLength; i++) {
    final block = await _f(secretKey, nonce, firstInput, i);
    result.setAll(macLength * i, block);
  }

  // Return bytes
  if (numberOfBytes == result.lengthInBytes) {
    return SecretKey(result);
  }
  return SecretKey(List<int>.unmodifiable(Uint8List.view(
    result.buffer,
    result.offsetInBytes,
    numberOfBytes,
  )));
}