Quick way to encrypt your objects in Java

Hi, hope you have a good Christmas :) Mine was not bad, but here I am to write a little more.
Besides eating chocolates, these days I have continued some of my school works. One in specific is a game for android, that soon I will talk more in detail.

 
One important thing in games is the possibility of save the scores in a way that no one can forge, at least directly. So how do this in Java?

The simplest idea that I remembered was to put the scores in a particular class, make it serializable, apply a xor and write it to a file, to recover do the reverse process.