Obfuscate Mobile Business Logic, Anti-Reversing in Android Apps

Learn to Obfuscate App Logic in Android apps, in mobile CI/CD with a Data-Driven DevSecOps™ build system.

What is code obfuscation?

One of the most used types of reverse engineering is static code analysis, where an attacker attempts to analyze the source code of an iOS or Android application in order to understand what the source code does and how it does it – all without running the app.

While there are many different methods and techniques to obfuscate mobile application code, Obfuscating App Logic is an effective way of preventing attackers from using static code analysis to understand the application’s logical flow, especially when combined with other obfuscation techniques such as binary code obfuscation and application shielding.

How does Appdome implement code obfuscation?

When enabling Appdome’s Obfuscate App Logic feature, the obfuscation of package names and dynamic classes, are included automatically. This functionality simplifies the process, making it seamless to incorporate robust code protection without necessitating manual adjustments for these components.

Detailed Features of Appdome’s Code Obfuscation:

• Excluding Specific Classes:
  Excluding a class from obfuscation necessitates the exclusion of the whole package to which the class belongs. This is due to the access rules inherent to Java classes.
  In the process of obfuscating a package, Appdome changes it entirely. However, any excluded classes still retain the non-obfuscated package name. Therefore, when an obfuscated class tries to access a non-obfuscated class (the excluded one), Java may raise an ‘illegal access exception’ despite both classes residing under the same package name in the original non-obfuscated app.
  To prevent such cases, once a class is excluded, the class package is excluded.
  In order to exclude classes, you will need to add the package of the classes you wish to exclude. For instance, excluding the class “com/appdome/test/TestClass” involves adding either “com/appdome/test” or “com.appdome.test” to the Exclude Specific Classes list.

• Multilingual Obfuscation:
  When using only ASCII characters for obfuscation, it is easier to follow a flow using reverse engineering tools such as JADX or hooking methods using hacking tools such as Frida. Appdome’s new obfuscation mechanism, Multilingual Obfuscation adds another layer of protection to the app’s obfuscation, significantly complicating any attempts made by an attacker to reverse engineer the application and deconstruct the code, thereby enhancing its security.  Appdome’s Multilingual Obfuscation method, differs from standard methods in that it uses Unicode characters, and a novel runtime algorithm as opposed to traditional ASCII characters, this complexity significantly complicates attempts to deconstruct the code, thereby enhancing its security.

Note: The Multilingual Obfuscation feature is supported on Android 8.0 and above. Please be aware that if the app is obfuscated using Unicode characters, you will not be able to install this app on Android 7.1.1 or earlier versions.

Prerequisites for Using Obfuscate App Logic:

To use Appdome’s mobile app security build system to Obfuscate App Logic , you’ll need:

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

Obfuscate App Logic on Android apps using Appdome

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

2. Build the feature: Obfuscate App Logic.

   1. Building Obfuscate App Logic by using Appdome’s DEV-API:

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

      Figure 1: Fusion Set that will contain the Obfuscate App Logic 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 Obfuscate App Logic feature via Appdome Console, to add the Obfuscate App Logic 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 Obfuscate App Logic feature via Appdome Console

      To build the Obfuscate App Logic 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™, Obfuscate App Logic is turned on by default, as shown below:

         Figure 3: Obfuscate App Logic 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) Obfuscate App Logic, as shown below.

         Figure 3: Obfuscate App Logic option

      3. When you select the Obfuscate App Logic you'll notice that your Fusion Set you created in step 2.1.1 now bears the icon of the protection category that contains Obfuscate App Logic

         

         Figure 4: Fusion Set that displays the newly added Obfuscate App Logic protection

      4. Optional Configuration with Obfuscate App Logic:

         1. Obfuscate Package Names

            Obfuscates package and class names within the application’s business logic.

         2. Obfuscate Dynamic Classes

            Obfuscates (renames) classes to random strings.

         3. Obfuscate Dynamic Methods

            Obfuscates (renames) methods to random strings.

         4. Obfuscate Linkages and Reflection

            Supports obfuscation of classes and methods used in reflection and in JNI up-calls and down-calls.

         5. Obfuscate Crashes

            Obfuscates methods and classes in crashes and stack traces.

         6. Exclude Specific Classes

            List class or package prefixes to exclude from obfuscation.

         7. Obfuscation Mapping File/Script

            Download mapping scripts and files in order to deobfuscate the app for further investigation.

         8. Multilingual Obfuscation

            Employs Unicode and unique algorithms, complicating reverse engineering attempts beyond standard ASCII obfuscation methods.

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

   Congratulations!  The Obfuscate App Logic protection is now added to the mobile app

3. Certify the Obfuscate App Logic feature in Android Apps.

   After building Obfuscate App Logic, Appdome generates a Certified Secure™ certificate to guarantee that the Obfuscate App Logic protection has been added and is protecting the app. To verify that the Obfuscate App Logic 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 Obfuscate App Logic has been added to each Android app. Certified Secure provides instant and in-line DevSecOps compliance certification that Obfuscate App Logic and other mobile app security features are in each build of the mobile app