Dex Relocation, Anti-Reversing for Android Apps

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

What is Dex Relocation?

In Android, compiled Java/Kotlin code resides in classes.dex files. Appdome’s Dex Relocation refers to a security technique that modifies a mobile app’s compiled code by obfuscating the logical control flow, thereby protecting Android apps against static code analysis and other forms of reverse engineering. The purpose of Dex relocation is to make reverse engineering tools ineffective and even unusable, making the code difficult to trace and understand.

Why Use Appdome's Dex Relocation?

Implementing Appdome’s Dex Relocation offers a crucial layer of protection for Android apps. By obfuscating the logical flow of the compiled code, it deters potential attackers by making the code significantly more difficult to decipher and exploit. In essence, Dex Relocation ensures the application’s integrity, safeguards user data, and protects the developer’s intellectual assets. To do this, Appdome uses several techniques such as applying call obfuscation to the compiled Java code and modifying the function call targets to obscure functions.

Appdome’s Dex Relocation doesn’t operate in isolation. When combined with Appdome’s TotalCode Obfuscation techniques, a reinforced protective layer emerges. These techniques complement and fortify each other, resulting in a comprehensive defense strategy that offers heightened resistance against potential threats.

Prerequisites for Using Dex Relocation:

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

• Appdome account (create a free Appdome account here)
• A license for Dex Relocation
• Mobile App (.apk or .aab for Android)
• Signing Credentials (see Signing Secure Android apps and Signing Secure iOS apps)

Use Dex Relocation on Android apps using Appdome

On Appdome, follow these 3 simple steps to create self-defending Android Apps that Use Dex Relocation 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 Relocation Compatible With: Java, JS, C++, C#, Kotlin, Flutter, React Native, Unity, Xamarin, Cordova and other Android apps

2. Build the feature: Dex Relocation.

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

      1. Create and name the Fusion Set (security template) that will contain the Dex Relocation feature as shown below:
      

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

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

      3. 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):

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

      4. 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 Relocation feature via Appdome Console

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

      1. Where: Inside the Appdome Console, go to Build > Security Tab > TOTALCode™ Obfuscation section.

         Like all other options in ONEShield™, Dex Relocation is turned on by default, as shown below:

         Figure 3: Dex Relocation option
         Note: The App Compromise Notification contains an easy to follow default remediation path for the mobile app end user. You can customize this message as required to achieve brand specific support, workflow or other messaging.

      2. How: Toggle (turn ON) Dex Relocation, as shown below.

         Figure 3: Use Dex Relocation option

      3. When you select the Dex Relocation 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 Relocation

         

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

      4. Extra Configuration with Dex Relocation:

         1. Favor Loading Time

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

         2. Exclude Specific Classes

            List class or package prefixes to exclude and not obfuscate.

         3. No Mapping File/Script

            Changes the flow logic, but does not rename functions. No mapping file or script needed.

      5. Click Build My App at the bottom of the Build Workflow (shown in Figure 3).

   Congratulations!  The Dex Relocation protection is now added to the mobile app

3. Certify the Dex Relocation feature in Android Apps.

   After building Dex Relocation, Appdome generates a Certified Secure™ certificate to guarantee that the Dex Relocation protection has been added and is protecting the app. To verify that the Dex Relocation protection has been added to the mobile app, locate the protection in the Certified Secure™ certificate as shown below:

   Figure 5: Certified Secure™ certificate

   Each Certified Secure™ certificate provides DevOps and DevSecOps organizations the entire workflow summary, audit trail of each build, and proof of protection that Dex Relocation has been added to each Android app. Certified Secure provides instant and in-line DevSecOps compliance certification that Dex Relocation and other mobile app security features are in each build of the mobile app