encryt.dart

    final Uint8List iv = Uint8List.fromList('Initialization Vector'.codeUnits);

    Future<String> encrypt(String message) async {

    // 1. 
     aesGcmSecretKey = await AesGcmSecretKey.
    (derivedBits);

    // 2.
      List<int> list = message.codeUnits;
      Uint8List data = Uint8List.fromList(list);

    // 3.
      Uint8List encryptedBytes = await aesGcmSecretKey.encryptBytes(data, iv);

    // 4.
      String encryptedString = String.fromCharCodes(encryptedBytes);
      print('encryptedString $encryptedString');
      return encryptedString;
    }