Reverse engineering of android java app using apktool, dex2jar, jd-gui to convert .apk file to .java.

By reverse engineering of android app (.apk file) we can get following :

• understand how a particular UI in an App is constructed
• reading AndroidManifest.xml – permissions, activities, intents etc in the App
• native libraries and images used in that App
• obsfucated code ( android SDK, by default, uses ProGuard tool which shrinks, optimizes, and obfuscates your code by removing unused code and renaming classes, fields, and methods with semantically obscure names.

Required Tools :

Download the followings first.

• Dex2jar from http://code.google.com/p/dex2jar/
• JD-GUI from http://java.decompiler.free.fr/?q=jdgui
• ApkTool from http://code.google.com/p/android-apktool/

Using ApkTool

– to extract AndroidManifest.xml and everything in res folder(layout xml files, images, htmls used on webview etc..)

Run the following command :

>apktool.bat d sampleApp.apk

It also extracts the .smali file of all .class files, but which is difficult to read.

##You can achieve this by using zip utility like 7-zip.

Using dex2jar

– to generate .jar file from .apk file, we need JD-GUI to view the source code from this .jar.

Run the following command :

 >dex2jar sampleApp.apk

Decompiling .jar JD-GUI

– it decompiles the .class files (obsfucated- in case of android app, but readable original code is obtained in case of other .jar file). i.e., we get .java back from the application.

Just Run the

jd-gui.exe and File->Open to view java code from .jar or .class file.

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Reference: Android Reverse Engineering – decompile .apk-.dex-.jar-.java from our JCG partner Ganesh Tiwari at the GT’s Blog blog.