Security / Android

APKs

How to reverse engineering an APK, edit the code and recompile the APK?

1. Decompile the apk:
   apktool d application.apk
2. Use MobSF or jadx-gui to analyze the source code.
3. Edit the desired part of the smali code extracted in step 1.
4. Rebuild the modified apk:
   apktool b -f -d application
5. Move the apk:
   mv application/dist/application.apk application-edited.apk
6. Generate a key (you will prompted to choose a password, remember it):
   keytool -genkey -v -keystore my-release-key.keystore -alias alias_name -keyalg RSA -keysize 2048 -validity 10000
7. Sign the apk:
   jarsigner -verbose -sigalg SHA1withRSA -digestalg SHA1 -keystore my-release-key.keystore application-edited.apk alias_name
8. Verify the apk:
   jarsigner -verify -verbose -certs application-edited.apk
9. Zipalign the apk for optimal loading:
   zipalign -v 4 application-edited.apk application-edited-aligned.apk

^{References: Decompile and recompile android APK, apktool documentation and BEGINNER’S GUIDE TO SMALI CODING}