decapsulate method

@override Future<Uint8List> decapsulate(Uint8List secretKey, Uint8List ciphertext)

Recover the shared secret from ciphertext using secretKey.

Implementation

@override
Future<Uint8List> decapsulate(
    Uint8List secretKey, Uint8List ciphertext) async {
  if (secretKey.length != seedLength) {
    throw ArgumentError.value(secretKey.length, 'secretKey',
        'X-Wing secret key must be the $seedLength-byte seed');
  }
  if (ciphertext.length != ciphertextLength) {
    throw ArgumentError.value(ciphertext.length, 'ciphertext',
        'X-Wing ciphertext must be $ciphertextLength bytes');
  }
  final Uint8List ctM = ciphertext.sublist(0, _mlKemCiphertextLength);
  final Uint8List ctX = ciphertext.sublist(_mlKemCiphertextLength);

  final _Expanded e = await _expand(secretKey);
  try {
    final Uint8List ssM =
        await _mlKem.decapsulate(e.mlKemKeyPair.secretKey, ctM);
    final Uint8List ssX = await _x25519.dh(e.x25519Secret, ctX);
    return _combine(ssM, ssX, ctX, e.x25519Public);
  } finally {
    _mlKem.releaseKeyPair(e.mlKemKeyPair);
  }
}