How to Obfuscate Kotlin Code in Android Apps

Last updated November 29, 2023 by Appdome

Learn to Enforce viewing and modifying Kotlin classes in Android apps, in mobile CI/CD with a Data-Driven DevSecOps™ build system.

What is Kotlin?

Kotlin is a cross-platform programming language, which is designed to fully interoperate with Java. For several years Kotlin has been approved by Google as a preferred language for Android app developers.

Since 2017, Kotlin has been included in Android Studio as an alternative to the standard Java compiler.

Why does Kotlin Need its Own Obfuscation?

Kotlin code has a section called metadata, which is found on each class file produced by the Kotlin compiler. Kotlin metadata holds important information about Kotlin classes. This information is crucial for Kotlin reflection, namely: a set of language and library features that allow inspecting, loading, and interacting with classes, fields, and methods at runtime.

Kotlin metadata holds not only information retrieved from the code itself, such as methods and variables but also additional information. As a result, this section requires its own obfuscation as part of the Kotlin obfuscation. In addition, each Kotlin version has its own metadata version, which affects its obfuscation.

As part of Appdome’s Total Code Obfuscation, Kotlin obfuscation is enabled by default for Kotlin versions 1.3.72 and higher.

Prerequisites for Using Kotlin Obfuscation:

To use Appdome’s mobile app security build system to Enforce viewing and modifying Kotlin classes , you’ll need:

Enforce viewing and modifying Kotlin classes on Android apps using Appdome

On Appdome, follow these simple steps to create self-defending Android Apps that Enforce viewing and modifying Kotlin classes 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. Kotlin Obfuscation Compatible With: Java, JS, C++, C#, Kotlin, Flutter, React Native, Unity, Xamarin, Cordova and other Android apps
  2. Build the feature: Kotlin Obfuscation.

    1. Building Kotlin Obfuscation by using Appdome’s DEV-API:

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

        Figure 1: Fusion Set that will contain the Kotlin Obfuscation 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 Kotlin Obfuscation feature via Appdome Console, to add the Kotlin Obfuscation 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 Kotlin Obfuscation feature via Appdome Console

      To build the Kotlin Obfuscation protection by using Appdome Console, follow the instructions below.

      1. Where: Inside the Appdome Console, go to Build > Security Tab > TOTALCode™ Obfuscation section.
      2. When you enable 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 Kotlin Obfuscation

        Fusion Set applied Kotlin Obfuscation

        Figure 4: Fusion Set that displays the newly added Kotlin Obfuscation protection

      3. Click Build My App at the bottom of the Build Workflow (shown in Figure 3).
    Congratulations!  The Kotlin Obfuscation protection is now added to the mobile app
  3. Certify the Kotlin Obfuscation feature in Android Apps.

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

    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 Kotlin Obfuscation has been added to each Android app. Certified Secure provides instant and in-line DevSecOps compliance certification that Kotlin Obfuscation and other mobile app security features are in each build of the mobile app


Using Appdome, there are no development or coding prerequisites to build secured Android Apps by using Kotlin Obfuscation. 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 Kotlin Obfuscation

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:

Related Articles:

Non-Native Code Obfuscation, Anti-Reversing for Android & iOS Frameworks

Obfuscate iOS Control Flows & Methods, Anti-Reversing iOS Apps

Dex Control Flow Relocation, Anti-Reversing for Android Apps

 

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

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