Secure Local Storage in Flutter

In this article, you will learn how to implement secure local storage in flutter apps.

If you have experience with front-end web development, you know we use the browser's local storage to store data in key-value pairs. Similarly, we can store data in flutter apps too, but this implementation's under the hood working is a little different as data is getting encrypted.

• 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.

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

Implementation

We will use a flutter plugin called flutter_secure_storage .

Add the following to your pubspec.yaml file:

dependencies:
  ...
  flutter_secure_storage: ^4.2.0

Check for the latest version on the plugin's page.

Configure Android Version

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

android {
  ...
  defaultConfig {
    ...
    minSdkVersion 18
    ...
  }
}

Create Instance

Import flutter_secure_storage in your file and create an instance of it.

import 'package:flutter_secure_storage/flutter_secure_storage.dart';

FlutterSecureStorage _localStorage = new FlutterSecureStorage();

Write Data

To insert a key-value pair in the storage, we will use the write method.
We need to pass key and value to this method.

await _localStorage.write(key: key, value: value);

• key and value should be a string.
• If the key already exists, the value will get replaced.
• If we pass a null value and the key already exists, it will get deleted.
• Its return type is void.

Read Data

To read a value for a particular key, we will use the read method.
We need to pass the key to this method.

await _localStorage.read(key: key);

• key should be a string.
• If the key exists, the value will be returned.
• If the key doesn't exist the null will be returned.
• Its return type is always a string.

Read All Data

To read all the values, we will use the readAll method.

await _localStorage.readAll();

• It will return all the key-value pairs as a Map.

Delete Data

To delete an entry, we will use the delete method.
We need to pass the key to this method.

await _localStorage.delete(key: key);

• key should be a string.
• Its return type is void.

Delete All Data

To delete all entries, we will use the deleteAll method.

await _localStorage.deleteAll();

• Its return type is void.

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Originally published on blog.bibekkakati.me