davodm/dgcrypt-android

Dgcrypt

Dgcrypt - Android is a simple Android library for encryption and decryption using AES-256-CBC. It supports both Kotlin and Java, and is designed to securely decrypt data that was encrypted on a backend, such as a PHP server using the Dgcrypt PHP library.

Platform Compatibility

The Dgcrypt library is designed to work seamlessly across multiple platforms. You can find corresponding libraries for the following platforms:

• PHP: Dgcrypt-PHP
• Node.js: Dgcrypt-Node

These libraries allow you to easily decrypt data that was encrypted on the backend using this PHP library, ensuring secure communication between your backend and client applications.

Installation

Add the library to your project:

1. Add the JitPack repository to your build file. Add it in your root build.gradle at the end of repositories:

dependencyResolutionManagement {
    repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
    repositories {
        mavenCentral()
        maven { url 'https://jitpack.io' }
    }
}

2. Add the dependency:

dependencies {
    implementation 'com.github.davodm:dgcrypt-android:1.0.0'
}

Usage

Kotlin

Encrypting Data:

val key = "your-32-character-long-key"
val iv = "your-16-character-iv"
val plainText = "Hello, World!"

try {
    val encrypted = Dgcrypt.encrypt(plainText, key, iv)
    println("Encrypted: $encrypted")
} catch (e: Exception) {
    e.printStackTrace()
}

Decrypting Data:

val key = "your-32-character-long-key"
val iv = "your-16-character-iv"
val encryptedText = "your-encrypted-text"

try {
    val decrypted = Dgcrypt.decrypt(encryptedText, key, iv)
    println("Decrypted: $decrypted")
} catch (e: Exception) {
    e.printStackTrace()
}

Java

Encrypting Data:

String key = "your-32-character-long-key";
String iv = "your-16-character-iv";
String plainText = "Hello, World!";

try {
    String encrypted = Dgcrypt.encrypt(plainText, key, iv);
    System.out.println("Encrypted: " + encrypted);
} catch (Exception e) {
    e.printStackTrace();
}

Decrypting Data:

String key = "your-32-character-long-key";
String iv = "your-16-character-iv";
String encryptedText = "your-encrypted-text";

try {
    String decrypted = Dgcrypt.decrypt(encryptedText, key, iv);
    System.out.println("Decrypted: " + decrypted);
} catch (Exception e) {
    e.printStackTrace();
}

Best Practices for Securing the Master Key

To further enhance the security of the master key, consider the following best practices:

1. Use Firebase Remote Config: Store the master key in Firebase Remote Config and fetch it at runtime. This way, you can easily update the master key without having to release a new version of your app.

import com.google.firebase.remoteconfig.FirebaseRemoteConfig;
import com.google.firebase.remoteconfig.FirebaseRemoteConfigSettings;

public class RemoteConfigHelper {
    private FirebaseRemoteConfig mFirebaseRemoteConfig;
    
    public RemoteConfigHelper() {
        mFirebaseRemoteConfig = FirebaseRemoteConfig.getInstance();
        FirebaseRemoteConfigSettings configSettings = new FirebaseRemoteConfigSettings.Builder()
            .setMinimumFetchIntervalInSeconds(3600)
            .build();
        mFirebaseRemoteConfig.setConfigSettingsAsync(configSettings);
    }
    
    public void fetchAndActivate() {
        mFirebaseRemoteConfig.fetchAndActivate().addOnCompleteListener(task -> {
            if (task.isSuccessful()) {
                String masterKey = mFirebaseRemoteConfig.getString("master_key");
                // Use the master key
            } else {
                // Handle the error
            }
        });
    }
}

2. SharedPreferences: Securely Store Secrets Using Encrypted SharedPreferences You can use EncryptedSharedPreferences to securely store the encrypted master key locally.

import androidx.security.crypto.EncryptedSharedPreferences;
import androidx.security.crypto.MasterKeys;
import android.content.Context;
import android.content.SharedPreferences;

public class SecureStorageHelper {
    private SharedPreferences encryptedSharedPreferences;

    public SecureStorageHelper(Context context) throws Exception {
        String masterKeyAlias = MasterKeys.getOrCreate(MasterKeys.AES256_GCM_SPEC);
        encryptedSharedPreferences = EncryptedSharedPreferences.create(
            "secure_prefs",
            masterKeyAlias,
            context,
            EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
            EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM
        );
    }

    public void storeEncryptedKey(String encryptedKey) {
        SharedPreferences.Editor editor = encryptedSharedPreferences.edit();
        editor.putString("encrypted_master_key", encryptedKey);
        editor.apply();
    }

    public String getEncryptedKey() {
        return encryptedSharedPreferences.getString("encrypted_master_key", null);
    }
}

License

This project is licensed under the MIT License - see the LICENSE file for details.

Author

Davod Mozafari - Twitter