[mpnordland]

Essentially anti cheat software in reverse. Instead of the client proving it is unmodified to the server, the server must prove itself unmodified to the client. You may be able to get somewhere by studying how open source network games prove they aren't modified to the server if they do that sort of thing.

[icebraining]

Which they don't; they just make it harder to pretend they aren't modified. Cheating is very much still possible, and more still if you wrote it all yourself.