Research On Fair Contract Signing Protocol

With the popularity of Internet and advances in science and technology,e-commerce has been rapid development,more and more contracts are signed online,the commitment to the signed contract is produced by the way of digital signature.In addition to meet some of the traditional information security needs,online signing as a new form of economic activity,it also needs to meet some new security features,like the feature of fairness and non-abuse.The electronic contract signing protocol is about how to exchange the digital signatures of the electronic contract between two mutually distrusted subjects on an open network in a fair way so that at end of the protocol either both parties get an effective digital signature from each other or neither side get.Because the electronic contract signing protocol plays an important role in the field of e-commerce,it draws a lot of experts and scholars to research.In this paper,we make a study on the electronic contract signing protocol.This paper first introduces some mathematical principles and basic cryptography concepts related to contract signing protocols.Then it classifies and summarizes the contract signing protocols,and we mainly focus on the study of optimistic contract signing protocol,we have summarized the basic model of the optimistic contract signing protocol and concluded several realization ideas of this kind of protocol,and we also compared the advantages and disadvantages of each protocol designed by these different ideas.Secondly,for the defect of off-line contract signing protocols:this kind of protocols require that the third party is completely reliable,they assume that the third party will not collude with one of the parties involved in the protocols,and sometimes this is hard to achieve in the real life,this paper designs a distributed semi-trusted third party's fair electronic contract signing protocol model by using the convertible undeniable signature algorithm and the publicly verifiable secret sharing principle,then we give a concrete implementation scheme which can not only satisfies some traditional securities features,like non-repudiation,privacy,integrity,but it also satisfies the security feature of non-abuse,that is,none of the two parties can show the validity of intermediate results to others.besides it can reduce the reliance on trusted third parties,so that the protocol has a better fairness.Finally,this paper discusses some related algorithms involved in the designed contract signing protocol,including the generation chosen algorithm,the inverse calculation algorithm of the modulo n multiplicative group,and the Lagrangian Interpolation algorithm over the finite filed for solving the recovery of the shared secret.And we have used the OpenSSL library to program the modules of the protocol,and the result verifies the correctness and feasibility of the protocol.