An Optimistic non-repudiation protocol with transparent trusted third party

In this paper we consider a new and efficient optimistic nonrepudiationprotocol. In a non-repudiation protocol, during which Alicewants to transmit a message to Bob, Alice has to send a non-repudiationof origin evidence to Bob (attesting that Alice is at the origin of thetransmitted message), and Bob has to send a non-repudiation of receiptevidence to Alice (attesting Bob’s receipt of the message). Classical solutionspropose to use a trusted third party to help realizing the exchangewithout giving any significant advantage to one of the two parties. Inan optimistic protocol, the trusted third party intervenes only in case ofproblems during the communication between Alice and Bob. Classically,in a situation where an error occurs, evidences that have been digitallysigned by the TTP are issued. Although these evidences are distinct fromthose produced by Alice and Bob in a faultless case, they have the samevalue in case of a dispute. In this paper we propose a protocol where theTTP produces the same evidences that Alice and Bob should have producedin a faultless protocol execution (this prevents, after a succesfulprotocol execution, to determine whether the TTP was involved or not).4th International Conference on Information Security. Springer-Verlag. Malaga, SpainSCOPUS: cp.k