Do I need cryptology for my app if I'm using google play games plugin ?

I have finished my app and I’m not quite sure if I have to add some cryptology methods to my game to make it secure.
I don’t run any adds,neither sell stuff in game.

What exactly do you want to secure? If you don’t have in-app purchases and you log in with GPG, then what is really left to secure? Do you have your own server that communicates with the app?