CheatProof Playout for Centralized and Distributed Online Games

1
Cheat-Proof Playoutfor Centralized and
Distributed Online Games

• Baughman, Levine
• U.of Massachusetts
• INFOCOM 2001

2
General Idea

• Cheating is prevalent in online games
• Some kinds of cheats (the authors think) are
• Suppress-Correct
• Lookahead
• Knowledge of others secrets
• They introduce protocol improvements to address
  each
  

3
Terminology

• Client/server vs. distributed
• Client/server provides more control, not enough,
  they claim
  
• Dead reckoning compensation for latency by
  guessing where players position is
  
• They claim the servers do this for clients
• Seems like this is only done by clients
• Bucket synchronization
• One bucket per time unit, with players moves as
  received
  
• Missing moves are dead reckoned from previous
  bucket(s)
  

4
Suppress-Correct Cheat

• Assume bucket synchronizing server
• Server drops you after n missed client updates,
  dead reckons up to that
  
• Miss n-1 updates, use the later knowledge of game
  state to send an advantageous nth move. Oooh.
  
• One solution is the stop and wait protocol
• No dead reckoning
• Get each players moves, then move to next state

5
Lookahead Cheat

• Under stop-and-wait protocol
• Under distributed games
• Be the last one to send out your move
• Oooh you gain one frame

6
Contribution No More Lookahead Cheats for
Distributed Games

• Use a stop-and-wait protocol called LockStep
• Solve the lookahead cheat with hashes
• Players send hashes of their decisions to each
  other
  
• Then they send their actual moves
• All can verify the moves and hashes go together
• Disadvantage slow

7
Contribution Faster LockStep

• Enhanced version only does LockStep playout for
  players within each others Sphere of Influence
  

8
Why These Dont Wow Me

• I believe clients dead reckon, servers dont
  there is no suppress-correct cheat
  
• There are stop-and-wait games. But the time
  resolution is very fine. One extra move is lost
  in the noise
  
• LockStep requires knowledge of where all players
  are
  

9
Last, Best Contribution Secret Possesions

• For distributed games
• Case 1 clients all know what secrets players
• Case 2 clients can lie about what they have
• Currently we have Case 1
• Move to Case 2, but players send out promise
  messages with hashes of what they have
  
• Verified by 3rd party