1. Cheating at Multiplayer Online Games Bruce Maggs (with some slides from An-Cheng Huang)

2. A small confession… Your professor is a notorious cheater

3. PLATO Computer System PLATO IV Developed by the University of Illinois and the Control Data Corporation 1961 timesharing PLATO II begins 1964 invention of plasma panel 1968 PLATO IV begins Spun off as “NovaNET” late 1980’s Revived at www.cyber1.org

4. Innovations first LARGE on-line community invention of the plasma panel multimedia “personal notes” – email “group notes” – newsgroups “consulting mode” – desktop sharing widely used “term talk” (like Unix talk) Shared memory enabled multiplayer games IBM correctly attributes Lotus Notes to PLATO

5. Hardware Control Data mainframes designed by Seymour Cray Cyber 70, 176, CDC 6600, 7600 Magnetic core memory 60-bit words, 6-bit characters One’s-complement arithmetic Up to 1000 simultaneous users (NovaNET runs on Alpha today?)

6. PLATO IV Terminal 512x512 plasma panel 1200 baud connection to mainframe Stream of commands for displaying text and symbols, and for drawing lines https://digitalanalogues.wordpress.com/2011/04/22/it-really-is-deja-vu-all-over-again/

7. Multiplayer Games Dungeons and Dragons –e.g., oubliette, avatar Space –e.g., spasim, empire Warfare –e.g., airfight, panther

8. Empire

9. Empire Basics I am  shrike , a proud Klingon / Kazari Becoming a member of the Federation, a Vulcan/Orion, or a Romulan is equivalent to turning in your private key The goal is to conquer the universe Ship fires phasers, photon torpedos Firing at correct angle inflicts more damage. To fire phasers at angle 233, type “f 233 NEXT” Ship makes a hyperjump when you replot the screen, based on time since last replot

10. Empire

11. The Clone Brothers I built a device that you plugged a keyboard into, and then it plugged into two separate PLATO IV terminals Small circuit waited for both terminals to acknowledge keystroke before telling keyboard Why? Fly two ships to same location in empire, then have double the firepower! Nicknamed the “Clone Brothers” device migrated to different clusters of PLATO terminals around campus at U of I

12. PLATO V Terminal Plasma panel and CRT versions Same 512 x 512 display 8080 processor implemented all graphics

13. PLATO V Terminal From http://plato.filmteknik.com/

14. Empire Bot 8080 had access to stream of commands sent to terminal from mainframe I wrote assembly code to determine angles to enemies on the screen (using an arctan look-up table) Program displayed exact angle above each enemy, with keyboard shortcuts to fire phasers or torpedos at that angle Also displayed a growing ellipse around ship to indicate distance of hyperjump Possibly the first shooter-game bot - 1979? (“shoot’ em up” or “arcade shooter” genre)

15. Avatar

16. Avatar Basics Players join different guilds, e.g., fighter, magician, cleric, and gain different capabilities Players form groups and enter the dungeon together to fight monsters and gather treasures At one time possibly most popular multi- player on-line game in the world Co-authored with David Sides and Andrew Shapira, with help from many others My current character is dead on level one

17. Avatar

18. Duplicating Magical Items Strategy: give all of your magical items and gold to a friend, the crash the game before the changes to your character are recorded to disk! Negative: “unfair” and throws the game economy out of whack Positive: we quickly find out about serious bugs

19. Best Consulting Gig Ever I am hired by Jagex, maker of Runescape to document that third-party bots really work My character is exempted from being banned for using bots My kids complain that I am a cheater

20. Runescape

21. How do the bots work? Runescape is a Java applet Bot maker provides Java applet container Bot does not scrape the screen, but instead examines the byte code Bot determines position on screen of character, objects, etc.

22. Anti-Bot Measures Code is rearranged in different instances of applet Ultimately, all data stored in one master array, permuted in random order, killing bots! Many players quit when bots were defeated

23. First-Person Shooter Games played over the Internet

24. Latency Compensation in Half-Life [Bernier GDC01] Naïve approach: dumb client    Player1 render player1 at (x1,y1) forward render player1 at (x1,y1) Response time for player: round-trip to server + server processing

25. Predicting Where I Am    Player1 render player1 at (x1,y1) forward render player1 at (x1,y1) render player1 at (x1,y1) render player1 at (x1,y1) render player1 at (x4,y4) forward

26. Predicting Where You Are Updates about other players’ locations not continuous Extrapolation (dead reckoning) –At last update, player2 is at (x1,y1) facing N with speed S  It should be at (x2,y2) now –Not good: in FPS, player movement very non-deterministic Interpolation –Impose an “interpolation delay” for rendering Update1 (x1,y1) Update2 (x2,y2) Update3 (x3,y3) Now Int. delay Now time

27. Lag Compensation Interpolation introduces a fixed lag (int. delay) –E.g., always see where you were 100 ms ago –Need to lead the target when aiming –Require players to extrapolate! Server-side lag compensation –Server uses the old location to compute hit/miss –Allows natural aiming/shooting –Possible weird experiences for players being fired upon  tradeoff for better game play

28.    P1 P2 P3 Fair Message Exchange [Guo et al. NG03] Look at “fairness” in client-server games room    P1 P2 P3 (1 ms) P2 (3 ms) P1 (4 ms)

29. Fair Message Exchange (2) Different latencies can make the game “unfair” P1 P2 P3 Server time t=0 (RTT 5) (RTT 10) (RTT 15) 3 t=8 P2 1 t=11 P3 t=19 4 P1

30. Fair Message Exchange (3) Fair-ordering delivery without synchronized clocks (a simple case) P1 P2 P3 Server t=0 (RTT 5) (RTT 10) (RTT 15) 3 t=8 P2 1 t=11 P3 t=19 4 P1 P2,3,18 P3,1,16 P2,3,18 t=16 P2,3,18 P3 t=18 P2 Server waits (here 15) before performing action. Ordering based on response time.

31. Cheating Strategy Introduce artificial delay between client and server Lie about how long it took to respond (or take advantage of server thinking update was received last) Server will think client was first to shoot, even though it receives message last

32. Cheat-Proof Playout [Baughman & Levine INFOCOM01] Two types of cheats –“Suppress-correct cheat” under dead reckoning (extrapolation) –“Lookahead cheat”  P1  P2  ? predict  ? here  P2 here, actually

33. Cheat-Proof Playout [Baughman & Levine INFOCOM01] Two types of cheats –“Suppress-correct cheat” under dead reckoning (extrapolation) –“Lookahead cheat” game advances in frames  P1  P2 fire do nothing  P1  P2 fire duck

34. Texture Hacks! transparent