An Efficient and Secure Event Signature (EASES) Protocol for Peer-to-Peer Massively Multiplayer Online Games Mo-Che Chan, Shun-Yun Hu and Jehn-Ruey Jiang Adaptive Computing and Networking Lab. National Central University 1

Outline Background Related work – NEO – SEA The proposed scheme – EASES Evaluation Conclusion 2

Background - MMOG Multiplayer online game Massively multiplayer online game (MMOG) 3

Background - architectures Client-server 4

Background - architectures Server-cluster 5

Background - architectures Peer-to-peer (P2P) network Efficiently maintain the topology – Virtual environment 6

Background – game logic In client-server and server-cluster – Server maintains game states – Users send event to server – Server sends information to player 77 time round

Background – cheat problem Game logic is maintained by peers in P2P environments. Some players may gain advantages unfairly. 8

Background - commitment Play the paper, scissors, rock game remotely without arbiter 9

Background – hash function Cryptographic hash function Strength depends on the following infeasibilities – For any given hashed value, to find M or M’ – For any given message M, to find H(M) = H(M’) – To find any pair (M, M’) such that H(M) = H(M’) 10 Hash function

Background - commitment No one can get unfair advantages if the hash function is secure. 11 First send H(Choice | Random) Then send (Choice | Random) H(Choice | Random) Choice | Random H(Choice | Random) Choice | Random

Background – digital signature Concept 12 A documentTo sign it No one can forge Signer can’t repudiate that he executed the algorithm for this document Authenticity of the document …….. Signature algorithm A digital signature ……..

Background – digital signature To sign a message 13 message 0101… …110 message 1011…110 Hash function To sign by sender’s private key

Background – digital signature To verify a signature 14 message 1011… …101 ? Hash function To inverse the signature by signer’s public key To check they are the same or not

Related work - NEO 15 Player i Every updating message Signing event updating message Encrypting the signed message After, send decrypting key

Related work - SEA 16 Player i Every updating message Signed hash value of event updating message After, send the plain message

The problem that we observed Digital signature algorithms are too slow. 17 Single Document Hash algorithm Signature algorithm Signature Original message To produce the message digest To sign the message digest

The objective To efficiently sign many discrete messages 18 Message 1 Message 2 …… Message n

The proposed EASES Initialization phase – Every player prepares the keys for signing. Signing phase – Every player signs his messages. Verification phase – Every receiver verifies the authenticity. Re-initialization phase – Re-generate new signing keys. 19

EASES – initialization phase 20 …… …110

EASES – signing & verification 21 ……. Send out j j j-1 j j j+1 j+2 j-1 j-2 j-3

EASES – re-initialization phase Re-execute initialization phase A more efficient way – Reserve the last two keys 22 …… …110 ……..

Evaluation - performance Computational cost – Hash replaces signature function Memory consumption – 1,000 * 192 bits = 24,000 bytes, when n = 1,000 Bandwidth consumption – Length of Hash value is short than signature’s 23 EASESTraditional Signature ComputationBetter MemoryBetter BandwidthBetter

Evaluation - security Unforgeability – No one can claim that he signed M, unless he show the OSK of M. – This requirement is secure if adopted cryptographic hash function is secure. Verifiability – Hash function is public. 24

Conclusion and discussion EASES is proposed to sign many discrete messages at once efficiently Security of EASES is as strong as those of traditional signature schemes ESAES implies the commitment property 25