Reverse engineering of Android Apps

First of all you must get the .apk-file.

- Therefore you have to connect your Android-Phone with your computer over USB.
- If not already installed, load the Android SDK from here https://developer.android.com/sdk/index.html
- Open a terminal and navigate to Android SDK/platform-tools
- Run following command ./adb pull /data/app/-.apk
(You can find the package-name of the application in the market-url. For Example by https://play.google.com/store/apps/details?id=com.rovio.angrybirds the packe-name is "com.rovio.angrybirds". The Number is mostly 1 or 2.)
- Now you have the apk-file in the same folder on your computer and you can decompile it. Therefore there are 2 things you can do, so make two copies of the apk-file.
1. To get the graphics and layouts you have to download a tool named apktool from here http://code.google.com/p/android-apktool/
When the tool and the apk-file are in the same folder you can decompile it from the terminal with the following command:
./apktool d [PACKAGE-NAME]-[Nr].apk
Now you get a new folder with the whole project. You can't read the java-code, but the graphics and layouts are origin. If you want to do some funny stuff, you can replace so graphics and build a new apk with the comman
./apktool b [FOLDER] FUN_[PACKAGE-NAME]-[Nr].apk
You can install this apk running ./adb install FUN_[PACKAGE-NAME]-[Nr].apk
2. To get the java-files as a jar, so you can get a closer look to the package-structure and classes you have to rename your apk-file to jar and unzip it.
Now you have a classes.dex-file, which you can compile to smali-files with the following tool:
https://code.google.com/p/smali/
So after the dex->smali compiling you get the whole project but with smali-files instead of class-files. But the smali-files are a bit understandable, so sometimes it is possible to change the right code-snippet to get what you want.
If you don't want to change anything, you can compile back smali->dex with the same baksmali-tool.
Now download the last tool: https://code.google.com/p/dex2jar/
With this one you can compile the classes.dex-file to a jar-file, which you can include as a normal java-lib into your Andrpod project.

And that's it!