APK modification

First, decompile apk file with apktool:

apktool d <file_name>.apk

Replace assets or edit Manifest.xml. smali2java can be of use for code modifications.

Recompile apk:

apktool b <file_name>

Alignment is necessary for modern android versions (I believe, 30+ SDK):

zipalign -v -f -p 4 <file_name>/dist/<file_name>.apk aligned-<file_name>.apk

Create a signing key. Fields values do not matter. Especially for personal use.

keytool -genkey -v -keystore my-release-key.keystore -alias alias_name -keyalg RSA -keysize 2048 -validity 1000

Actually sign apk with it:

apksigner.jar sign -ks my-release-key.keystore --ks-key-alias alias_name aligned-<file_name>.apk

It will overwrite the provided apk with a signed one.

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