biometric_storage

Encrypted file store, optionally secured by biometric lock for Android, iOS, MacOS and partial support for Linux, Windows and Web.

Meant as a way to store small data in a hardware encrypted fashion. E.g. to store passwords, secret keys, etc. but not massive amounts of data.

• Android: Uses androidx with KeyStore.
• iOS and MacOS: LocalAuthentication with KeyChain.
• Linux: Stores values in Keyring using libsecret. (No biometric authentication support).
• Windows: Uses wincreds.h to store into read/write into credential store.
• Web: Warning Uses unauthenticated, unencrypted storage in localStorage. If you have a better idea for secure storage on web platform, please open an Issue.

Check out AuthPass Password Manager for a app which makes heavy use of this plugin.

Getting Started

Installation

Android

• Requirements:

  • Android: API Level >= 23 (android/app/build.gradle minSdkVersion 23)

  • Make sure to use the latest kotlin version:

    • android/build.gradle: ext.kotlin_version = '1.4.31'

  • MainActivity must extend FlutterFragmentActivity

  • Theme for the main activity must use Theme.AppCompat thme. (Otherwise there will be crashes on Android < 29) For example:

    android/app/src/main/AndroidManifest.xml:

    <activity
        android:name=".MainActivity"
        android:launchMode="singleTop"
        android:theme="@style/LaunchTheme">
        [...]
        <meta-data
              android:name="io.flutter.embedding.android.NormalTheme"
              android:resource="@style/NormalTheme"
              />
    </activity>

    android/app/src/main/res/values/styles.xml:

    <resources>
      <style name="LaunchTheme" parent="Theme.AppCompat.NoActionBar">
        ...
      </style>
      <style name="NormalTheme" parent="Theme.AppCompat.NoActionBar">
        ...
      </style>
    </resources>

Resources

• https://developer.android.com/topic/security/data
• https://developer.android.com/topic/security/best-practices

iOS

https://developer.apple.com/documentation/localauthentication/logging_a_user_into_your_app_with_face_id_or_touch_id

• include the NSFaceIDUsageDescription key in your app’s Info.plist file
• Supports all iOS versions supported by Flutter. (ie. iOS 12)

Known Issue: since iOS 15 the simulator seem to no longer support local authentication: https://developer.apple.com/forums/thread/685773

Mac OS

• include the NSFaceIDUsageDescription key in your app’s Info.plist file
• enable keychain sharing and signing. (not sure why this is required. but without it You will probably see an error like:

  SecurityError, Error while writing data: -34018: A required entitlement isn't present.

• Supports all MacOS Versions supported by Flutter (ie. >= MacOS 10.14)

Usage

You basically only need 4 methods.

1. Check whether biometric authentication is supported by the device

  final response = await BiometricStorage().canAuthenticate()
  if (response != CanAuthenticateResponse.success) {
    // panic..
  }

2. Create the access object

  final store = BiometricStorage().getStorage('mystorage');

3. Read data

  final data = await storageFile.read();

4. Write data

  final myNewData = 'Hello World';
  await storageFile.write(myNewData);

See also the API documentation: https://pub.dev/documentation/biometric_storage/latest/biometric_storage/BiometricStorageFile-class.html#instance-methods