How to patch android apps which detect rooted system

I've run into apps which checked for being rooted or have a custom ROM. As Magisk was not always an option I decided to patch these apps.

Guide for retrieving, decompiling, modifying and recompiling an app

• Get it from the phone

  adb shell pm list packages | grep adb shell pm path <app.package.name> adb pull data/app/<app.package.name>-==/base.apk

• First install framework, then decompile and test if it builds
  ('-f -r and aapt2' used as for me apk does not build by default)

  apktool if <app.package.name> apktool d -f -r --use-aapt2 <app.package.name>.apk apktool b -f -r --use-aapt2 <app.package.name>

• Modify the code

Search for root checker libraries in smali_classes directory. Usually they use some popular library like rootbeer. Check the consts as most probably they contain the blacklisted super user apps' package names. They also test super user by su binary, test-keys method, or some other way, take care of them as well. Overwriting them with some non-existent package name, file path is enough. After you have edited the code just build the app.

• Create keystore first then sign

  keytool -genkey -v -keystore my-release-key.keystore -alias android_rel -keyalg RSA -keysize 2048 -validity 10000 jarsigner -verbose -sigalg SHA1withRSA -digestalg SHA1 -keystore my-release-key.keystore /<app.package.name>/dist/<app.package.name>.apk android_rel zipalign -v 4 /<app.package.name>/dist/<app.package.name>.apk <app.package.name>_signed.apk

• Upload and install or install directly

  adb push /<app.package.name>_signed.apk /sdcard/ adb -d install -r <app.package.name>_signed.apk

• Check for diffs

  diff -q -r <app.package.name>.apk <app.package.name>.apk_ diff -Nau > file.patch diff -Naur <app.package.name> <app.package.name>_