flutter_secure_storage

A Flutter plugin to store data in secure storage:

• Keychain is used for iOS
• AES encryption is used for Android. AES secret key is encrypted with RSA and RSA key is stored in KeyStore. By default following algorithms are used for AES and secret key encryption: AES/CBC/PKCS7Padding and RSA/ECB/PKCS1Padding From Android 6 you can use newer, recommended algoritms: AES/GCM/NoPadding and RSA/ECB/OAEPWithSHA-256AndMGF1Padding You can set them in Android options like so:

  AndroidOptions _getAndroidOptions() => const AndroidOptions(
       keyCipherAlgorithm: KeyCipherAlgorithm.RSA_ECB_OAEPwithSHA_256andMGF1Padding,
       storageCipherAlgorithm: StorageCipherAlgorithm.AES_GCM_NoPadding,
    );

  On devices running Android with version less than 6, plugin will fall back to default implementation. You can change the algorithm, even if you already have some encrypted preferences - they will be re-encrypted using selected algorithms. Choosing algorithm is irrelevant if you are using EncryptedSharedPreferences as described below.

• With v5.0.0 we can use EncryptedSharedPreferences on Android by enabling it in the Android Options like so:

  AndroidOptions _getAndroidOptions() => const AndroidOptions(
  encryptedSharedPreferences: true,
  );

  For more information see the example app.

• libsecret is used for Linux.

Note KeyStore was introduced in Android 4.3 (API level 18). The plugin wouldn't work for earlier versions.

Important notice for Web

flutter_secure_storage only works on HTTPS or localhost environments. Please see this issue for more information.

WASM support

You can opt-in into the new WASM compatible version of flutter_secure_storage_web by adding the following override in your pubspec.yaml:

dependency_overrides:
  flutter_secure_storage_web: ^2.0.0-beta.1

Platform Implementation

Please note that this table represents the functions implemented in this repository and it is possible that changes haven't yet been released on pub.dev

Getting Started

If not present already, please call WidgetsFlutterBinding.ensureInitialized() in your main before you do anything with the MethodChannel. Please see this issue for more info.

import 'package:flutter_secure_storage/flutter_secure_storage.dart';

// Create storage
final storage = FlutterSecureStorage();

// Read value
String value = await storage.read(key: key);

// Read all values
Map<String, String> allValues = await storage.readAll();

// Delete value
await storage.delete(key: key);

// Delete all
await storage.deleteAll();

// Write value
await storage.write(key: key, value: value);

This allows us to be able to fetch secure values while the app is backgrounded, by specifying first_unlock or first_unlock_this_device. The default if not specified is unlocked. An example:

final options = IOSOptions(accessibility: KeychainAccessibility.first_unlock);
await storage.write(key: key, value: value, iOptions: options);

Configure Android version

In [project]/android/app/build.gradle set minSdkVersion to >= 18.

android {
    ...

    defaultConfig {
        ...
        minSdkVersion 18
        ...
    }

}

Note By default Android backups data on Google Drive. It can cause exception java.security.InvalidKeyException:Failed to unwrap key. You need to

• disable autobackup, details
• exclude sharedprefs FlutterSecureStorage used by the plugin, details

Configure Web Version

Flutter Secure Storage uses an experimental implementation using WebCrypto. Use at your own risk at this time. Feedback welcome to improve it. The intent is that the browser is creating the private key, and as a result, the encrypted strings in local_storage are not portable to other browsers or other machines and will only work on the same domain.

It is VERY important that you have HTTP Strict Forward Secrecy enabled and the proper headers applied to your responses or you could be subject to a javascript hijack.

Please see:

• https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Strict-Transport-Security
• https://www.netsparker.com/blog/web-security/http-security-headers/

application-specific key option

On the web, all keys are stored in LocalStorage. flutter_secure_storage has an option for the web to wrap this stored key with an application-specific key to make it more difficult to analyze.

final _storage = const FlutterSecureStorage(
  webOptions: WebOptions(
    wrapKey: '${your_application_specific_key}',
    wrapKeyIv: '${your_application_specific_iv}',
  ),
);

This option encrypts the key stored in LocalStorage with WebCrypto wrapKey. It is decrypted with WebCrypto unwrapKey when used. Generating and managing application-specific keys requires careful attention from developers. See (https://github.com/mogol/flutter_secure_storage/issues/726) for more information.

Configure Linux Version

You need libsecret-1-dev and libjsoncpp-dev on your machine to build the project, and libsecret-1-0 and libjsoncpp1 to run the application (add it as a dependency after packaging your app). If you using snapcraft to build the project use the following

parts:
  uet-lms:
    source: .
    plugin: flutter
    flutter-target: lib/main.dart
    build-packages:
      - libsecret-1-dev
      - libjsoncpp-dev
    stage-packages:
      - libsecret-1-0
      - libjsoncpp-dev

Apart from libsecret you also need a keyring service, for that you need either gnome-keyring (for Gnome users) or ksecretsservice (for KDE users) or other light provider like secret-service.

Configure MacOS Version

You also need to add Keychain Sharing as capability to your macOS runner. To achieve this, please add the following in both your macos/Runner/DebugProfile.entitlements and macos/Runner/Release.entitlements (you need to change both files).

<key>keychain-access-groups</key>
<array/>

If you have set your application up to use App Groups then you will need to add the name of the App Group to the keychain-access-groups argument above. Failure to do so will result in values appearing to be written successfully but never actually being written at all. For example if your app has an App Group named "aoeu" then your value for above would instead read:

<key>keychain-access-groups</key>
<array>
    <string>$(AppIdentifierPrefix)aoeu</string>
</array>

If you are configuring this value through XCode then the string you set in the Keychain Sharing section would simply read "aoeu" with XCode appending the $(AppIdentifierPrefix) when it saves the configuration.

Configure Windows Version

You need the C++ ATL libraries installed along with the rest of Visual Studio Build Tools. Download them from here and make sure the C++ ATL under optional is installed as well.

Integration Tests

Run the following command from example directory

flutter drive --target=test_driver/app.dart

Contributing

If you want to contribute, you need to initialise the workspace after cloning the repo with melos like this:

flutter pub get
melos bootstrap

After that, everything should be set up and working!