12/13/2001CS 638, Fall 2001 Today Cheat prevention (and cheat techniques) –Great article: Evaluations

12/13/2001CS 638, Fall 2001 Why Care About Cheats? Online gaming is big business Cheats can achieve financial advantage: –Competitive games with prizes are the obvious example (casinos) –Also consider EverQuest: People play the game, build good characters, and then auction them on Ebay. If they can cheat to obtain good characters, they are achieving unfair financial advantage Cheats can ruin the game for everyone: –Players tend to have a strong sense of fairness –If they believe they are being cheated, they will not play, and you will not make any money Single player cheaters typically only affect themselves, so you don’t care

12/13/2001CS 638, Fall 2001 Sources of Cheats Reflex augmentation: Use a cheat to improve some aspect of physical performance, such as the firing rate or aiming Authoritative clients: Clients issue commands that are inconsistent with the game-play, or mimic the server Information Exposure: Clients obtain information that should be hidden Compromised servers: A hacked server biases game-play toward the group that knows of the hacks Bugs and Design Loopholes: Bugs are found and exploited, or parts of the program intended for one purpose are used for another Environmental Weakness: Differences or problems with the OS or network environment are exploited

12/13/2001CS 638, Fall 2001 Observations About Cheating Brewer’s rule: The only way to make a system 100% secure is to completely isolate it (Eric Brewer, 1996) Pritchard’s Rules (Gamasutra article): –If you build it, they will come - to hack and cheat –Hacking attempts increase as a game becomes more successful –Cheaters actively try to control knowledge of their cheats –Your game, along with everything on the cheater’s computer, in not secure - not memory, not files, not devices and networks –Obscurity is not security –Any communication over an open line is subject to interception, analysis and modification –There is no such thing as a harmless cheat –Trust in the server is everything in client-server games –Honest player would like the game to tip them off to cheater, hackers hate it

12/13/2001CS 638, Fall 2001 Reflex Augmentation Aiming proxies intercept communications, build a map of where people are, and automatically shoot them Rapid-fire proxies take each “shoot” packet and replicate it Fix #1: The server validates player actions - if they are too good the player is considered a cheat and kicked out –Problem is calibration: You have to find the cheats while not penalizing excellent players Fix #2: Make it difficult to insert non-valid packets –Encrypt the packets, but your encryption must be cheap, and cheap encryption can be broken –Make the encryption depend on the game state or other time-dependent “random” value. Hard to do with UDP –If using guaranteed delivery (TCP) serialize packets with a unique sequence of numbers - cannot then replicate or insert extra packets

12/13/2001CS 638, Fall 2001 Authoritative Clients Occurs when one player’s game informs everyone else that a definitive event has occurred: e.g. I just got a power-up Hacked clients can be created in many ways: change the executable, change game data in other files, hack packets Fix is to insert command request steps: –Player request an action, its validity is checked, it is sent out on the network, and added to the player’s pending queue –Incoming actions also go on the pending queue –Actions come off the pending queue, are validated again, and then are implemented Sometimes validation is hard to get right, so try synchronization –Occasionally send complete game state around, and compare it –Actually, send something derived form complete game state

12/13/2001CS 638, Fall 2001 Information Exposure Some classics: Modify the renderer to make walls transparent, modify maps to remove the fog of war Basically, display variables must be modified in memory, or read out and displayed elsewhere –Hackers are very good at finding the locations of key data in memory, and modifying them transparently Fixes: –Check that players agree on the value of certain variables, and the validity of actions - synchronization again Note that you can look for actions that cannot be valid with the correct display –Compile statistics on drawing, and see of they look off (eg # polygons drawn) –Encrypt data in memory to avoid passive attacks

12/13/2001CS 638, Fall 2001 Compromised Servers Many servers have customization options, and the community is encouraged to modify the server –This is completely legal However, as a game become popular, naïve people start to play the game –They do not have the skills or knowledge to check that the server they are playing on is “pure” –They will grow frustrated, blame the developer, and complain to their friends Some modifications can be very insidious, and may not be legal. For example, hack the serve to do different damage for opponents, and small differences add up Solution is to warn people when they connect to the server, and about any other non standard properties (found through validation)

12/13/2001CS 638, Fall 2001 Bugs and Design Issues Some bugs enable cheating, such as a bug that enables fast reloading, or one that incorrectly validates commands Some design decisions make cheating easier: –Embedding cheats codes in single player mode makes it easy for a hacker to track down the variables that control cheats –Poor networking or event handling can allow repeat commands or other exploitations Age of Empires and Starcraft example: all resource management is done after all events for a turn are processed. Poor networking allowed multiple cancel events on the queue, which restored multiple resources Solution is to avoid bugs and think carefully about the implications of design decisions on hacking

12/13/2001CS 638, Fall 2001 Environmental Weaknesses Facilities to deal with the OS or network may leave you vulnerable to some forms of attack –Interaction with the clipboard can introduce non-printable characters –Interaction with almost any scripting language may leave you open to hacks not related to the game itself (ie your game could be a way in) –Network connection drops or overloading can cause problems Some cheats destroy the game for every player (tip the board) which can be useful if you are losing Others knock off a specific player (your worst enemy, one assumes)

12/13/2001CS 638, Fall 2001 The Moral of the Story You can’t win, you just try to make cheating as hard as possible and contain the damage