How to Encrypt Java Class Files (.dex) in Android Apps

Last updated March 7, 2024 by Appdome

Learn to Encrypt Dex Files in Android apps, in mobile CI/CD with a Data-Driven DevSecOps™ build system.

What is DEX File Encryption?

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. Appdome’s DEX File Encryption is a security feature uses Appdome’s APPCode Packer, the industry’s first no-code Android App Packer, to hide and encrypt all Java code of an Android app when the app is built by using Appdome. Using code packing with Appdome APPCode Packer makes the disasembling tools ineffective and even unusable. For details see White Hat Android Packer from Appdome.

Why Encrypt DEX Files (Java Classes) in Android apps?

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:

  1. 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.
  2. Decryption overhead is only incurred during the app’s first run, and even then has minimal impact.
  3. Since the DEX files are encrypted, they are protected by Appdome’s Anti-Tampering.
  4. 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.

Prerequisites for Using Dex File Encryption:

To use Appdome’s mobile app security build system to Encrypt Dex Files , you’ll need:

Encrypt Dex Files on Android apps using Appdome

On Appdome, follow these 3 simple steps to create self-defending Android Apps that Encrypt Dex Files without an SDK or gateway:

  1. Upload the Mobile App to Appdome.

    1. Upload an app to Appdome’s Mobile App Security Build System

    2. Upload Method: Appdome Console or DEV-API
    3. Android Formats: .apk or .aab
    4. Dex File Encryption Compatible With: Java, JS, C++, C#, Kotlin, Flutter, React Native, Unity, Xamarin, Cordova and other Android apps
  2. Build the feature: Dex File Encryption.

    1. Building Dex File Encryption by using Appdome’s DEV-API:

      1. Create and name the Fusion Set (security template) that will contain the Dex File Encryption feature as shown below:
      2. fusion set that contains Dex File Encryption

        Figure 1: Fusion Set that will contain the Dex File Encryption feature
        Note: Naming the Fusion Set to correspond to the protection(s) selected is for illustration purposes only (not required).

      3. Follow the steps in Sections 2.2.1-2.2.2 of this article, Building the Dex File Encryption feature via Appdome Console, to add the Dex File Encryption feature to this Fusion Set.

      4. Open the Fusion Set Detail Summary by clicking the “...” symbol on the far-right corner of the Fusion Set, as shown in Figure 1 above, and get the Fusion Set ID from the Fusion Set Detail Summary (as shown below): fusion Set Detail Summary image

        Figure 2: Fusion Set Detail Summary
        Note: Annotating the Fusion Set to identify the protection(s) selected is optional only (not mandatory).

      5. Follow the instructions below to use the Fusion Set ID inside any standard mobile DevOps or CI/CD toolkit like Bitrise, App Center, Jenkins, Travis, Team City, Cirlce CI or other system:
        1. Build an API for the app – for instructions, see the tasks under Appdome API Reference Guide
        2. Look for sample APIs in Appdome’s GitHub Repository
    2. Building the Dex File Encryption feature via Appdome Console

      To build the Dex File Encryption protection by using Appdome Console, follow the instructions below.

      1. Where: Inside the Appdome Console, go to Build > Security Tab > TOTALData™ Encryption section.
      2. When you select the Dex File Encryption you'll notice that your Fusion Set you created in step 2.1.1 now bears the icon of the protection category that contains Dex File Encryption

        Fusion Set applied Dex File Encryption

        Figure 4: Fusion Set that displays the newly added Dex File Encryption protection

      3. Optional Configuration with Dex File Encryption:
        1. Favor Loading Time

          Automatically detect and optimize obfuscation of publicly available components in order to preserve application loading time.

      4. Click Build My App at the bottom of the Build Workflow (shown in Figure 3).
    Congratulations!  The Dex File Encryption protection is now added to the mobile app

Using Appdome, there are no development or coding prerequisites to build secured Android Apps by using Dex File Encryption. There is no SDK and no library to code or implement in the app and no gateway to deploy in your network. All protections are built into each app and the resulting app is self-defending and self-protecting.

Releasing and Publishing Mobile Apps with Dex File Encryption

After successfully securing your app by using Appdome, there are several available options to complete your project, depending on your app lifecycle or workflow. These include:

If you have any questions, please send them our way at or via the chat window on the Appdome platform.

Thank you!

Thanks for visiting Appdome! Our mission is to secure every app on the planet by making mobile app security easy. We hope we’re living up to the mission with your project.

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