How to Encrypt Java Strings in Android Apps

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

What are Strings?

In Android apps, strings are any text-based information stored in or used by the app (eg: Java strings, or strings.xml). Strings are often used to store and share text-based information such as usernames, passwords, authentication info, API keys, token, cookies, and more. Such data can be easily understood, and even extracted, from the application without using specialized tools.

Why Encrypt Strings in Android Apps?

Encrypting strings in Android apps is an important measure to protect the data from being harvested for malicious purposes. This feature enhances the security of the app against malicious attempts to read the app’s contents or harvest valuable data about users and organizations.

Detailed Features of Appdome’s TOTALData™ Encryption:

Advanced In-App Secrets Protection
Encrypt application specific sensitive data such as keys, shared secrets and tokens.

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.

Prerequisites for Using Encrypt Strings:

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

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

Encrypt Strings on Android apps using Appdome

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

2. Build the feature: Encrypt Strings.

   1. Building Encrypt Strings by using Appdome’s DEV-API:

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

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

      To build the Encrypt Strings protection by using Appdome Console, follow the instructions below.

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

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

         Figure 3: Encrypt Strings 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) Encrypt Strings, as shown below.
         If needed, Customize the Threat Notification to be displayed to the mobile end-user in a standard OS dialog notification when Appdome Encrypts Strings.

         Figure 3: Encrypt Strings 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.

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

         

         Figure 4: Fusion Set that displays the newly added Encrypt Strings protection

      4. Extra Configuration with Encrypt Strings:

         1. Encrypt Resources

            Encrypt all Android application assets.

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

   Congratulations!  The Encrypt Strings protection is now added to the mobile app

3. Certify the Encrypt Strings feature in Android Apps.

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