Secure SharedPreferences

Introduction

Shared Preferences are key-value based XML files. It is located under /data/data/package_name/shared_prefs/<filename.xml>.

So a user with root privileges can navigate to this location and can change its values. If you want to protect values in your shared preferences, you can write a simple encryption and decryption mechanism.

You should know tough, that Shared Preferences were never built to be secure, it's just a simple way to persist data.

Syntax

  1. public static String encrypt(String input);
  2. public static String decrypt(String input);

Parameters

ParameterDefinition
inputString value to encrypt or decrypt.

Remarks

Shared Preferences were never built to be secure, it's just a simple way to persist data.

It is not a good idea to use shared preferences for storing critical information such as user credentials. To save user credentials (such as passwords) you need to use other methods such as Android's AccountManager.

Securing a Shared Preference

Simple Codec

Here to illustrate the working principle we can use simple encryption and decryption as follows.

public static String encrypt(String input) {
    // Simple encryption, not very strong!
    return Base64.encodeToString(input.getBytes(), Base64.DEFAULT);
}

public static String decrypt(String input) {
    return new String(Base64.decode(input, Base64.DEFAULT));
}

Implementation Technique

public static String pref_name = "My_Shared_Pref";

// To Write
SharedPreferences preferences = getSharedPreferences(pref_name, MODE_PRIVATE);
SharedPreferences.Editor editor = preferences.edit();
editor.putString(encrypt("password"), encrypt("my_dummy_pass"));
editor.apply(); // Or commit if targeting old devices

// To Read
SharedPreferences preferences = getSharedPreferences(pref_name, MODE_PRIVATE);
String passEncrypted = preferences.getString(encrypt("password"), encrypt("default_value"));
String password = decrypt(passEncrypted);