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

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

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

  4. Background - architectures • Client-server

  5. Background - architectures • Server-cluster

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

  7. Background – game logic • In client-server and server-cluster • Server maintains game states • Users send event to server • Server sends information to player round time 7

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

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

  10. 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’) Hash function 010101110100

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

  12. Background – digital signature • Concept 010101000111010011001011 010011100110101000110101 011010111000110101010100 110100011010101010101001 010101010010101010101010 …….. 101001110100110010110110 101100110101000110101010 010111001011010101010011 010010110101010101010010 110110010101010101010111 …….. Signature algorithm A document To sign it A digital signature • No one can forge • Signer can’t repudiate that he executed the algorithm for this document • Authenticity of the document

  13. Background – digital signature • To sign a message To sign by sender’s private key Hash function message 0101…101 1011…110 message 1011…110

  14. Background – digital signature • To verify a signature message 1011…110 To inverse the signature by signer’s public key Hash function ? 0101…101 0101…101 To check they are the same or not

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

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

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

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

  19. 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.

  20. EASES – initialization phase …….. 1011…110

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

  22. EASES – re-initialization phase • Re-execute initialization phase • A more efficient way • Reserve the last two keys …….. …….. 1011…110

  23. 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

  24. 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.

  25. 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