Abstract: This paper presented an extension of CS logic which is a type of knowledge logic and can be used to analyze the properties of non-reputation protocols with timeliness. Using the extended logic, we proved the improved ZG protocol and found a reply attack on signature message of the protocol. As a result, it is not satisfied with non-repudiation property. The example shows the non-reputation protocols with timeliness can be effectively analyzed by the extended CS logic.

Key words: Non-repudiation protocol, CS logic, Timeliness, Non-reputation, Fairness