Reversing

In this part we will extract the legitimate apk from emulator or the device and get the source code.

First Steps

# install tools
apt install adb apktool openjdk-11-jdk-headless zipalign apksigner
 
# list android attached devices
adb devices
 
# find app name
adb shell pm list packages -f | grep $app_name
 
# list installed packages
adb shell pm list packages -f
 
# get path of the app we want to reverse
adb shell pm path $package_name
 
# get the app on our local machine on current folder
adb pull $PATH_app .

Get the source code

Tools :

• jadx / jadx-gui
• dex2jar
• apktool
• apkx

jadx -d $path_output_folder app.apk
 
# or d2j
d2j-dex2jar.sh app.apk
 
# or apktool decompile
apktool d app.apk -o $output_folder
 
# or apkx
apkx app.apk
cd app
# open in visual studio
code .
 
# or use jadx-gui
jadx-gui app.apk
# Open the JAR file with JD-GUI and you’ll see its Java code.

Decompile/Compile Source Code

## Install app on android device
adb install app.apk
 
# decompile
apktool d app.apk -o app-decompile 
 
# remove app from phone 
adb uninstall app.apk
 
# recompile
apktool b app-decompile/ -o app.apk
 
# sign
# create keystore
keytool -genkey -v -keystore demo.keystore -alias demokeys -keyalg RSA -keysize 2048 -validity 10000
# sign the apk
jarsigner -sigalg SHA1withRSA -digestalg SHA1 -keystore demo.keystore -storepass demopass app.apk demokeys
## apksigner supports signature v1 to v4
apksigner sign --ks demo.keystore --ks-pass pass:$password app.apk
 
# verify the signature
jarsigner -verify app.apk
# zipalign the APK
zipalign 4 app.apk app_signed.apk
 
# also for signing :
## d2j-apk-sign
d2j-apk-sign app.apk -o app-signed.apk
 
## uber-apk-signer
java -jar uber-apk-signer.jar --apks app.apk