Cheating at Multiplayer Online Games AnCheng Huang Bruce

Cheating at Multiplayer Online Games An-Cheng Huang Bruce Maggs

A small confession… Your professor is a notorious cheater

Types of MOG: Categorization by Genre • First-Person Shooter (FPS) • Role-Playing Game (RPG) • Real-Time Strategy (RTS)

First-Person Shooter (FPS) Game world Player character Weapons Aim + shoot Call of Duty, Activision / Infinity Ward

FPS (cont. ) Game world

Role-Playing Game (RPG) Game world Player character “Weapons” Accomplish task, improve (virtual) ability, accomplish harder task, etc. Diablo II, Blizzard Entertainment / Blizzard North (? )

RPG (cont. ) Game world

Real-Time Strategy (RTS) Game world “Units” Explore, build, combat Rise of Nations, Microsoft

RTS (cont. ) Game world

Categorization by Persistency • No persistency • Persistent player information • Persistent game world • Persistency – Local: e. g. , run a persistent server for a few friends – Global: e. g. , game company hosts servers for all

No Persistency Before gaming session During After

Persistent Player Information Before gaming session During After

Persistent Game World Before gaming session During After

Interesting Combinations n: Number of players in a game world • n<=64 (16 -32 mostly), no persistency, FPS: e. g. , Co. D • n<=8 (2 -4 mostly), no persistency, RTS: Ro. N • n<=8, persistent player information, RPG: Diablo II • n>1000, persistent game world, RPG: Ever. Quest • n>1000, persistent game world, FPS: Planet. Side

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 “Nova. NET” late 1980’s • Revived at www. cyber 1. org

Innovations • • • first LARGE on-line community invention of the plasma panel multimedia (built-in slide projector!) “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

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 • (Nova. NET runs on Alpha today? )

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

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

Empire

Empire Basics • I am shrike , a proud Klingon / Kazari • Becoming a member of the Federation, a Vulcan/Orion, or a Romulan is equivalent to rooting for UNC • 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

Empire

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

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

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

First-Person Shooter 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-person shooter bot? 1979?

Avatar

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

Avatar

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

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

Runescape

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.

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

Latency Compensation in Half-Life • [Bernier GDC 01] • Naïve approach: dumb client render player 1 at (x 1, y 1) Player 1 forward render player 1 at (x 1, y 1) Response time for player: round-trip to server + server processing

Predicting Where I Am render player 1 atat(x 1, y 1) at at(x 1, y 1) (x 4, y 4) Player 1 forward forward render player 1 at (x 1, y 1)

Predicting Where You Are • Updates about other players’ locations not continuous • Extrapolation (dead reckoning) – At last update, player 2 is at (x 1, y 1) facing N with speed S It should be at (x 2, y 2) now – Not good: in FPS, player movement very non-deterministic • Interpolation – Impose an “interpolation delay” for rendering Now Int. delay Now Update 3 (x 3, y 3) Update 2 (x 2, y 2) time Update 1 (x 1, y 1)

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

Fair Message Exchange • [Guo et al. NG 03] • Look at “fairness” in client-server games P 1 (4 ms) room P 3 P 2 (3 ms) P 3 (1 ms) P 1 P 2

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

Fair Message Exchange (3) • Fair-ordering delivery without synchronized clocks (a simple case) P 3 P 2, 3, 18 P 3, 1, 16 P 2, 3, 18 Server t=0 t=8 t=11 t=16 t=18 P 2 (RTT 5) P 1 3 P 3 (RTT 10) P 2 (RTT 15) P 3 P 1 1 4 Server waits (here 15) before performing action. Ordering based on response time. t=19

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

Cheat-Proof Playout • [Baughman & Levine INFOCOM 01] • Two types of cheats – “Suppress-correct cheat” under dead reckoning (extrapolation) predict P 2 P 1 here, actually – “Lookahead cheat” P 2 ? ? here

Cheat-Proof Playout • [Baughman & Levine INFOCOM 01] • Two types of cheats – “Suppress-correct cheat” under dead reckoning (extrapolation) – “Lookahead cheat” game advances in frames do nothing duck P 2 P 1 fire

Security • How are cheaters actually cheating in reality? “Duping” in D 2 (persistent player) A B Crash server (s. t. not saved) A Exit & save B Maphack for RTS (should only see occupied area) modify game client to display everything

Security (2) • Video card driver / texture, auto-aim / auto-shoot bots transparent