This document discusses decompiling Android applications. It provides an overview of the Android compilation process, including resource and interface code generation, Java compilation, byte code conversion, packaging, signing, and optimization. It also discusses tools for decompiling APK files, such as Bytecode Viewer and android-apktool. Additionally, it covers how ProGuard can be used to obfuscate code and protect applications from reverse engineering during the decompilation process.

1. Decompiling Android
applications

2. Decompiling Android apps
• quick overview of the compilation process!
• tools for decompiling!
• approach and overview of the results!
• how does proguard fit in the game?

3. !
!
!
!
!
• Android compilation process [1]
Resource
code
generation
Interface
code
generation
Java
compilation
Byte code
conversion
Packaging
Application
signing
Package optimization

4. Resource / Interface code generation
• inputs: AndroidManifest.xml, drawables, values,
strings, styles …!
• outputs: R.java!
• .aidl files are converted to Java interfaces
Application
resources
R.java
Application
source code
.aidl files
Java
Interfaces
aapt aidl

5. Java compilation / Byte code conversion
• annotation processing and
code generation (apt)!
• *.java -> *.class (javac)!
• all *.class files -> .dex file (dex)!
• this includes .class files from
.jar and .aar libs!
• in some cases there are
more .dex files
R.java
Application
source code
Java
Interfaces
apt
Generated
source code
javac
.class files

6. Android bytecode
• Android uses a modified JVM called
Dalvik!
• multiple classes are bundled into a
single .dex file!
• fun fact: .dex has a limit of total 65k
methods in all classes
.class files
dex
.dex files

7. Packaging
• resources compiled with aapt!
• .dex files!
• other resources from
“src/main/resources” folder!
• result: unsigned and
unoptimized .apk file
.dex files
Application
resources
aapt
apkbuilderCompiled
resources
Other
resources
.apk package

8. Signing / optimization
• .apk package is signed with a
keystore (jarsigner)!
• package is optimized (zipalign)
jarsigner
.apk package keystore
Signed
.apk package
zipalign
Signed and
optimized.apk

9. Tools - Bytecode viewer [3]
• everything you need for decompiling in one tool!
• doesn’t have a way to extract resources!
• make sure you give it some time after it’s started
before decompiling anything (about 20s), otherwise
it will just freeze

10. Other tools
• JD-GUI - .jar decompiler with GUI!
• dex2jar - name says it all!
• android-apktool!
• unpackages .apk archive!
• useful for extracting manifest and resources

11. Decompilation result

12. Package files
• .apk, .aar and .jar packages are actually .zip files!
• in order to access manifest and all resources
from .apk use android-apktool!
• .aar contains .jar archive along with resources and
manifest!
• .jar package is a .zip file containing bytecode in
separate .class files

13. How to protect your code?
• use Proguard!
• adds an additional step after byte
code generation!
• removes unused code!
• renames classes, fields, methods
with obscure names!
• smaller .apk file!
• harder to reverse engineer
Byte code
conversion
Packaging
Code obfuscation

14. Enabling proguard
• just a quick reminder:!
• set minifyEnabled to true!
• create proguard rules file

15. Proguard example

16. Conclusion
• to decompile code use Bytecode viewer!
• to extract resources from .apk use android-apktools!
• use proguard to protect your code and make it
harder to obfuscate

17. References
• [1] http://www.herongyang.com/Android/Project-
Android-Application-Project-Build-Process.html!
• [2] https://developer.android.com/tools/building/
index.html!
• [3] https://github.com/konloch/bytecode-viewer!
• [4] https://code.google.com/p/android-apktool/

18. Contact
• @kustivan!
• https://github.com/ikust