Cryptanalysis of Three Event Signature Protocols for Peer-to-peer Massively Multiplayer Online Games

In 2008, Chan et al. presented an event signature (EASES) protocol for peer-to-peer massively multiplayer online games (P2P MMOGs). The authors declare that the EASES protocol is efficient and secure, and could achieve non-repudiation, event commitment, save memory, bandwidth and reduce the complexity of the computations. However, we find that Chan et al.’s EASES protocols are not secure and give the detailed steps to attack their protocol. Further, we point out their dynamic EASES protocol is also not secure and can be cracked by the attacker, the attacking result shows that attacker can even replace any update event he wants to forge. In 2010, Li et al. found a replay attack on the EASES protocol and proposed an enhanced edition to improve it. However, our works show their enhancement is still not secure as well. Finally, we made a discussion about this problem and point the weakness existence in these three protocols.