Abstract
Optimistic multiparty contract signing (OMPCS) protocols are proposed for exchanging multiparty digital signatures in a contract. Compared with general two-party exchanging protocols, such protocols are more complicated, because the number of protocol messages and states increases considerably when signatories increase. Moreover, fairness property in such protocols requires protection from each signatory rather than from an external hostile agent. It thus presents a challenge for formal verification. In our analysis, we employ and combine the strength of extended modeling language CSP# and linear temporal logic (LTL) to verify the fairness of OMPCS protocols. Furthermore, for solving or mitigating the state space explosion problem, we set a state reduction algorithm which can decrease the redundant states properly and reduce the time and space complexity greatly. Finally, this paper illustrates the feasibility of our approach by analyzing the GM and CKS protocols, and several fairness flaws have been found in certain computation times.
Highlights
The first optimistic multiparty contract signing protocol (OMPCS) was designed by Asokan et al in 1997 [1]
Based on modeling language CSP# and linear temporal logic, an efficient method which aims to analyze the fairness of optimistic multiparty contract signing protocols is presented in this paper
In order to demonstrate the feasibility of our method, two examples of the GM and CKS protocol have been described and several fairness attacking traces have been found
Summary
The first optimistic multiparty contract signing protocol (OMPCS) was designed by Asokan et al in 1997 [1]. Not so much attention has been paid to optimistic multiparty contract signing protocols, there have been several researchers who did certain remarkable work in the weak fairness verification field and got some achievements. CKS protocol and verified that the fairness can be guaranteed in the case of four Such method was used in [7] to analyze the fairness of MRT [8] and MR [9] protocols. This paper describes a precise and nature formulation of the desired weak fairness and universal OMPCS protocol models that includes multisignatories and contract texts promises simultaneously, formalizes protocol arithmetic, and considers composite attackers of the dishonest signatory.
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