PuKoren

# You must first install apktool (https://github.com/iBotPeaches/Apktool) and android SDK
# and decompile apk using it 
# apktool d -rf my-app.apk

# then generate a key for sign in:
# keytool -genkey -v -keystore my-release-key.keystore -alias alias_name -keyalg RSA -keysize 2048 -validity 10000
rm signed-app.apk
apktool b -f -d com.myapp
jarsigner -verbose -sigalg SHA1withRSA -digestalg SHA1 -keystore my-release-key.keystore com.myapp/dist/com.myapp.apk alias_name
zipalign -v 4 com.myapp/dist/com.myapp.apk signed-app.apk