How to encrypt a variable before storing it in the device via PlayerPrefs?

Hi, I store player's coins in PlayerPrefs for Android version of the game but it can easily be opened and hacked away. Is there any way to encrypt the integer and then store it via PlayerPrefs and then read it and decrypt and use it? I have an MD5 hash function for my leaderboard, so can I store it as MD5 hash and read it via MD5 hash or something like that? Like contacting it with a secret key and then computing MD5 hash over it. Thanks.