decryptString function

Future<String> decryptString(ASECombinedCipher cc, ASEPrivateKey sk)

Decrypts a string using the hybrid PKE scheme It uses the private key (sk) to generate a shared secret and then uses AES-GCM to decrypt the ciphertext (ct)

Implementation

Future<String> decryptString(ASECombinedCipher cc, ASEPrivateKey sk) async {
  var rRec = kemDecap(cc.kemCt, sk);
  var flatR = Uint8List.fromList(rRec.vec[0].coeffs);
  var aesKey = await deriveAesKeyWithSalt(flatR, cc.salt);

  try {
    final nonce = cc.nonce;
    final tagLen = 16;
    final ctLen = cc.ciphertext.length - tagLen;
    final cipherText = cc.ciphertext.sublist(0, ctLen);
    final mac = cc.ciphertext.sublist(ctLen);
    final secretBox = SecretBox(
      cipherText,
      nonce: nonce,
      mac: Mac(mac),
    );

    final clear = await aesGcm.decrypt(
      secretBox,
      secretKey: SecretKey(aesKey),
    );

    String result = utf8.decode(clear);
    secureWipe(flatR);
    secureWipe(aesKey);
    return result;
  } catch (e) {
    secureWipe(flatR);
    secureWipe(aesKey);
    throw StateError('Decryption failed: authentication error');
  }
}