encryption - Secure Online Highscore Lists for Non-Web Games

Question

I'm playing around with a native (non-web) single-player game I'm writing, and it occured to me that having a daily/weekly/all-time online highscore list (think Xbox Live Leaderboard) would make the game much more interesting, adding some (small) amount of community and competition. However, I'm afraid people would see such a feature as an invitation to hacking, which would discourage regular players due to impossibly high scores.

I thought about the obvious ways of preventing such attempts (public/private key encryption, for example), but I've figured out reasonably simple ways hackers could circumvent all of my ideas (extracting the public key from the binary and thus sending fake encrypted scores, for example).

Have you ever implemented an online highscore list or leaderboard? Did you find a reasonably hacker-proof way of implementing this? If so, how did you do it? What are your experiences with hacking attempts?

Answer 1

At the end of the day, you are relying on trusting the client. If the client sends replays to the server, it is easy enough to replicable or modify a successful playthrough and send that to the server.

Your best bet is to raise the bar for cheating above what a player would deem worth surmounting. To do this, there are a number of proven (but oft-unmentioned) techniques you can use:

1. Leave blacklisted cheaters in a honeypot. They can see their own scores, but no one else can. Unless they verify by logging in with a different account, they think they have successfully hacked your game.
2. When someone is flagged as a cheater, defer any account repercussions from transpiring until a given point in the future. Make this point random, within one to three days. Typically, a cheater will try multiple methods and will eventually succeed. By deferring account status feedback until a later date, they fail to understand what got them caught.
3. Capture all game user commands and send them to the server. Verify them against other scores within a given delta. For instance, if the player used the shoot action 200 times, but obtained a score of 200,000, but the neighboring players in the game shot 5,000 times to obtain a score of 210,000, it may trigger a threshold that flags the person for further or human investigation.
4. Add value and persistence to your user accounts. If your user accounts have unlockables for your game, or if your game requires purchase, the weight of a ban is greater as the user cannot regain his previous account status by simply creating a new account through a web-based proxy.