when I was using Flutter’s encrypt: ^5.0.3 dependence to encrypt and decrypt string data, I encountered the occasional unsolvable RangeError in release mode:

RangeError: Value not in range: -16

Here is my code:

import 'package:encrypt/encrypt.dart' as encrypt;

class EncryptedStorage {
  
  static final key = encrypt.Key.fromUtf8(randomString32);

  static final iv = encrypt.IV.fromUtf8(randomString16);

  static final encrypt.Encrypter encryptor = encrypt.Encrypter(
    encrypt.AES(
      key,
      mode: encrypt.AESMode.cbc, 
      padding: "PKCS7", 
    ),
  );

  static String getEncryptedString(String originalString) {
    final encrypt.Encrypted encrypted = encryptor.encrypt(originalString, iv: iv);
    return encrypted.base64; 
  }

  static String getStringByEncryptData(String encryptedData) {
    final String decrypted = encryptor.decrypt64(encryptedData, iv: iv);
    return decrypted;
  }
}

I’ve gotten this RangeError while I calling getOriginalStringByEncryptData(). And it’s always the value -16.
Does anyone know the cause of the error?

This error appears on some iPhone devices. It’s occasional. I don’t know how to reproduce this error.

Here is the detail of flutter doctor

[✓] Flutter (Channel stable, 3.22.1, on macOS 14.5 23F79 darwin-x64, locale en-GB)
[✓] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
[✓] Xcode - develop for iOS and macOS (Xcode 15.4)
[✓] Chrome - develop for the web
[✓] Android Studio (version 2023.3)
[✓] Android Studio (version 2021.2)
[✓] Android Studio (version 2021.2)
[✓] IntelliJ IDEA Ultimate Edition (version 2022.2.4)
[✓] IntelliJ IDEA Ultimate Edition (version 2022.2.1)
[✓] VS Code (version 1.89.1)