processBytes method

Uint8List processBytes(Uint8List inputBytes)

Returns a new Uint8List with the transformed inputBytes. Encryption and decryption are identical for ChaCha20. The initial state is preserved, so the method can be called repeatedly.

Implementation

Uint8List processBytes(Uint8List inputBytes) {
  final initial = Uint32List.fromList(chaChaState);
  final out = Uint8List(inputBytes.length);
  final keyStream = Uint8List(64);
  final bd = ByteData.sublistView(keyStream);

  for (int offset = 0, block = 0;
  offset < inputBytes.length;
  offset += 64, block++) {
    // Each block starts from the initial state with counter + j
    chaChaState = Uint32List.fromList(initial);
    chaChaState[12] = (initial[12] + block) & 0xFFFFFFFF;
    chaCha20();

    // Serialize explicitly as little-endian (RFC 7539, section 2.3)
    for (int i = 0; i < 16; i++) {
      bd.setUint32(i * 4, chaChaState[i], Endian.little);
    }

    // The last block may be shorter than 64 bytes
    final n = min(64, inputBytes.length - offset);
    for (int i = 0; i < n; i++) {
      out[offset + i] = inputBytes[offset + i] ^ keyStream[i];
    }
  }

  chaChaState = initial; // Restore the initial state
  return out;
}