Originally posted by: Ylen13
that will not keep people from cheating and i pretty sure someone have created cd key maker to creat a legal cd.
*smacks Ylen*
Much better. Now, it is in theory not possible to come up with a keygen that can generate valid keys for an online game such as Diablo, Warcraft, Quake 3, etc. The key here is that while the clients veryify keys, they do not know the whole fomula used to generate keys, so they'll pass both valid keys, and invalid(to the server) keys. Because a client can be reverse-engineered, it is possible to figure out the formula it knows, but not the whole formula, since none of the crackers have direct access to the master server to see the complete formula. Because of that, baring a stroke of luck, the best that can be done is a brute-force attack of different keys against the master server, in order to see which keys are valid, but with the keyspace out there, that's statistically impossible to pull off. No one has yet to defeat the Q3 master system, and I wouldn't be surprised if the same held true for the Diablo master system too.
PS 5489, my guess is that they just have a master black-list. So if your friend has a different key, he can still play, but if you use that key to cheat, and it gets black-listed too, then neither of you can play. It's technologically impossible to keep a person from playing, as they can always acquire another key by buying another copy(or proxy to defeat IP blacklists, disposable CCs to defeat CC blacklists, etc), but you can still discourage them