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All the existing non-repudiation protocols ensuring strong fairness have to assume that the communication channel between trusted third party (TTP) and each player is resilient at least. Where only unreliable channel can be guaranteed, all these protocols become impractical. In this study, based on smart card on the receiver side, the authors design a fair non-repudiation protocol that needs no assumptions on the communication channel. The smart card takes over the role of an online TTP server. Without a dedicated TTP server, this protocol is ideal for some ad hoc scenarios where no infrastructure is available. This protocol can also be easily modified to support fair exchange of time-sensitive data. Compared with other traditional security protocols, automatic formal verification of fair non-repudiation protocols is much harder to achieve. The authors use meta-reasoning method to prove that the fair exchange property of this protocol can be reduced to three secrecy properties that fall into the scope of today's most automatic verification tools and therefore can be easily verified. The authors also use a recently proposed automatic method to verify the non-repudiation properties and fairness property of our protocol.
Date of Publication: March 2010