How to Encrypt Java Class Files (.dex) in Android Apps
Learn how to encrypt DEX Files (Java Classes) in Android apps.
In recent years, decompilers have reached a maturity level that allows recovering source code from mobile app binaries with ease. Obfuscation has become a well-established preventive measure developers use against static reverse engineering attempts. There are several ways to implement obfuscation, but various obfuscation solutions differ in several things: Ease of use (e.g., specialized compilers and post-build tools), Performance (i.e., performance penalty, if any) and the reference threat level.
Since eventually all defenses can be broken, the quality of a good defense is measured by the amount of work, expertise and time needed to break the defense.
This Knowledge Base article provides step-by-step instructions for using Appdome to encrypt Java Class files (.dex) in Android apps.
We hope you find this knowledge base useful and enjoy using Appdome!
About DEX File Encryption
Appdome is a no-code mobile security and development platform that enables anybody to add a wide variety of security features, SDKs and APIs to Android and iOS applications. Using a simple ‘click to add’ user interface, anyone can easily encrypt Android Java Class files (.dex) in seconds, no-code or coding required.
Appdome’s DEX File Encryption is a security feature that encrypts the mobile app’s compiled Java code and decrypts it at run-time. Appdome’s DEX File Encryption, combined with other obfuscation features, makes reverse engineering an arduous task while preserving the functionality and performance of the original app. Appdome’s is compatible with mobile apps built in any development environment including Native Android apps, hybrid apps, and non-native apps built-in Xamarin, Cordova, and React Native, Ionic and more. This streamlines implementations, cuts development work, and ensures a guaranteed and consistent implementation of Appdome’s DEX File Encryption to any mobile app.
Why Encrypt DEX Files (Java Classes) in Android apps?
In Android, compiled Java/Kotlin code resides in
classes.dex files (see structure of Android applications). The common tools to reverse engineer DEX files are disassemblers such as baksmali and dex2jar and decompilers such as jadx and jdgui. The purpose of code packing with Appdome APPCode Packer is to make these tools ineffective and even unusable. To do this, Appdome encrypts all DEX files not needed for app initialization, making it impossible for disassemblers to find the original code. At run-time, Appdome’s code will decrypt the encrypted DEX files and allow the app to continue working as usual.
This obfuscation technique provides the following benefits:
- Trying to use offline reversing techniques on the application will fail as most classes will not be found in the APK or in the AAB.
- Decryption overhead is only incurred during the app’s first run, and even then has minimal impact.
- Since the DEX files are encrypted, they are protected by Appdome’s Anti-Tampering.
- In addition, any attempt to force this information out of the application using run-time methods will be thwarted by Appdome’s Anti-Debugging and other features in ONEShield.
This feature is complementary to Appdome’s Control-Flow Relocation and may be used together to further the app’s Java code reverse-engineering protection.
If your application was developed using a non-native framework such as React-Native, Cordova or Xamarin, you might want to check out Non-Native Code Obfuscation.
If, on the other hand, your application has more native code in it, we recommend you check out Binary Code Obfuscation.
Since the app still requires certain classes for its initial startup, specific classes mentioned by the following tags in the app’s manifest inside the “application” tag will not be encrypted:
- android: appComponentFactory
- android: name