decrypt function

Future<String> decrypt(Map<String, dynamic> keyStore, String passphrase)

Implementation

Future<String> decrypt(Map<String, dynamic> keyStore, String passphrase) async {
  Uint8List ciphertext = (keyStore['crypto']['ciphertext'] as String).toU8a();
  String kdf = keyStore['crypto']['kdf'];

  Map<String, dynamic> kdfparams = keyStore['crypto']['kdfparams'] is String
      ? json.decode(keyStore['crypto']['kdfparams'])
      : keyStore['crypto']['kdfparams'];
  var cipherparams = keyStore['crypto']["cipherparams"];
  Uint8List iv = (cipherparams["iv"] as String).toU8a();

  List<int> encodedPassword = utf8.encode(passphrase);
  _KeyDerivator derivator = getDerivedKey(kdf, kdfparams);
  List<int> derivedKey = derivator.deriveKey(encodedPassword);
  List<int> macBuffer =
      derivedKey.sublist(16, 32) + ciphertext + iv + ALGO_IDENTIFIER.codeUnits;

  String mac = (SHA256()
      .update(Uint8List.fromList(derivedKey))
      .update(macBuffer)
      .digest()
      .toHex());

  String macString = keyStore['crypto']['mac'];

  Function eq = const ListEquality().equals;
  if (!eq(mac.toUpperCase().codeUnits, macString.toUpperCase().codeUnits)) {
    throw 'Decryption Failed';
  }

  var aesKey = derivedKey.sublist(0, 16);
  var encryptedPrivateKey =
      (keyStore["crypto"]["ciphertext"] as String).toU8a();

  var aes = _initCipher(false, aesKey, iv);

  var privateKeyByte = aes.process(encryptedPrivateKey);
  return privateKeyByte.toHex();
}