Encrypt on RenPy (Phyton), decrypt on PHP

Hello everyone! I’m looking for a way to move a score from RenPy to a webserver using an URL, but in order players not to change it, it has to go encoded. So, the idea is to create a mathematical encryption in Ren'Py so when the player gets a score, the game makes something like this: $ player_score = 250 $ key = [login to view URL](10,99) … do something … $ player_score_encrypted = player_score * key imagebutton auto .... action OpenURL("[login to view URL]"+key+"&score="+player_score_encrypted) Then on the server side using PHP: $player_score_encrypted = (isset($_GET['score'])) ? $_GET['score'] : 0; $key = (isset($_GET['key'])) ? $_GET['key'] : 0; $player_score = $ player_score_encrypted / $key; Obviously, this is way to simple and anyone can guess the procedure to decipher it, so I need something way more complex so players cant cheat. I would prefer NOT to install any new library to the renpy since it only makes it heavier, a mathematical problem would be enough Thanks!