How can I edit APK's library files (.so files)?

Question

I want to install 2 different versions of an app. I researched a little and found that I need to change APK's package name with APK Editor. I decompiled the APK with APK Editor and changed everything related to the package name. For example, the app's package name was com.oldapk.filee, which I changed to com.newapk.file. Then I compiled it again and installed the new APK file. But I was unable to launch the new APK file.

I enabled USB Debugging on my phone and started to looking crash logs. I saw that the package name was mentioned as com.oldapk.filee, and I started thinking about what could be wrong. I used ack on Linux to check which files have the com.oldapk.filee string and saw that 2 libraries (.so files) was including the old package name. I changed them in NotePad++ (Hex Editor Addon) to the new package name, but this time when the app launched, I was able to see starting screen, but it was crashing in 0.5 seconds after I launched it. I checked the crash logs again and then I saw that the package name was still old. Maybe the changes that I made didn't affect it.

How can I edit these files?

Answer 1

Editing the package name of an existing app that you are not a developer can be a challenge. Also, unlike editing the Smali code, editing binary files can indeed break the app.

Here is some points that should be considered :

• The ack commands will only list strings and the name of the package can be encoded.

• Both APKs can use a same directory/file (e.g. in external storage), that maybe does not contains the package name, will lead to a crash due to permissions issue as the file/directory will be owned by the UUID of the com.oldapk.filee and cannot be accessed. To list the folders/files that are used by the application, these commands ADB shell commands can be used:

  • Get the user of the app com.oldapk.filee

  > ps -A | grep com.oldapk.filee
  u0_a230       10259    899 16984024 74060 0                   0 S 
  com.oldapk.filee
  

  • Get the list of files owned by the user of the app (u0_a230) on the /sdcard

  > find /sdcard/ -user u0_a230 
  

• In the binary, changing the package name with a another one that the length is not equal to the length of com.oldapk.filee will break the library (ensure that the '\0' 0x00 is the last byte of the string).

• Application can have an anti-tampering protection, it can be installed but crash if the app is tampered.

• Adding the flag android:debuggable="true" to the tag <application> on the "AndroidManifest.xml" can help debugging the tampered APK.

Hope that can help and good luck.