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.

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Background - commitment

• Play the paper, scissors, rock game remotely without arbiter

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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’)

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Hash function

010101110100

Background - commitment

• No one can get unfair advantages if the hash function is secure.

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First send H(Choice | Random)

Then send (Choice | Random)

H(Choice | Random)Choice | Random

H(Choice | Random)Choice | Random

Background – digital signature

• Concept

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A document To sign it

•No one can forge•Signer can’t repudiate that he executed the algorithm for this document•Authenticity of the document

010101000111010011001011010011100110101000110101011010111000110101010100110100011010101010101001010101010010101010101010……..

Signaturealgorithm

A digital signature

101001110100110010110110101100110101000110101010010111001011010101010011010010110101010101010010110110010101010101010111……..

Background – digital signature

• To sign a message

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message 0101…101 1011…110

message 1011…110

Hash functionTo sign by sender’s private key

Background – digital signature

• To verify a signature

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message 1011…110

0101…101 0101…101?

Hash functionTo inverse the signatureby signer’s public key

To check they are the same or not

Related work - NEO

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Player i1 1{ ( )} , , ( )rA

r r r rA A A A A AK

M S U K S V

• Every updating message• Signing event updating message• Encrypting the signed message

• After, send decrypting key

Related work - SEA

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Player i1 1 1

( , , , )

( , , , , )

r r rA A A

r r r r rA A A A A

Commit H U n SessID ID

M S Commit U Vh n r

• 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.

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SingleDocumen

t

Hash algorithm

Signature algorithm

Signature

Original message To produce themessage digest

To sign themessage digest

The objective

• To efficiently sign many discrete messages

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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.

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EASES – initialization phase

20…

….

.

1011…110

EASES – signing & verification

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…….

…….

Send out

j

j

j-1

j-1

j

j

j+1

j+1

j+2

j+2

j-1

j-1

j-2

j-2

j-2

j-2

j-3

j-3

EASES – re-initialization phase

• Re-execute initialization phase• A more efficient way– Reserve the last two keys

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……

..

1011…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

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EASES Traditional Signature

Computation Better

Memory Better

Bandwidth Better

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.

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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

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