An optimistic fair exchange (OFE) protocol is an effective tool helping two parties exchange their digital items in an equitable way with assistance of a trusted third party, called arbitrator, who is only required if needed. In previous studies, fair exchange is usually carried out between individual parties. When fair exchange is carried our between two members from distinct groups, anonymity...

Optimistic fair exchange (OFE) is a protocol for solving the problem of exchanging items or services in a fair manner between two parties, a signer and a verifier, with the help of an arbitrator which is called in only when a dispute happens between the two parties. In almost all the previous work on OFE, after obtaining a partial signature from the signer, the verifier can present it to others...

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Fair exchange is one of the most fundamental problems in secure distributed computation. Alice has something that Bob wants, and Bob has something that Alice wants. A fair exchange protocol would guarantee that, even if one of them maliciously deviates from the protocol, either both of them get the desired content, or neither of them do. It is known that no twoparty protocol can guarantee fairn...

In this paper we explore the overhead introduced by secure functions in considering a case study in non-repudiation. We present a model of an optimistic fair exchange protocol specified using the Markovian process algebra PEPA and present results derived using a fluid approximation and stochastic simulation. This system poses an interesting performance problem in that the degree overhead of the...

We propose a new protocol allowing the exchange of an item against a signature while assuring fairness. The proposed protocol, based on the Girault-Poupard-Stern signature scheme (a variation of the Schnorr scheme), assumes the existence of a trusted third party that, except in the setup phase, is involved in the protocol only when one of the parties does not follow the designated protocol or s...

Efficiency of optimistic fair exchange using trusted devices is studied. Pfitzmann, Schunter and Waidner (PODC 1998) have shown that four messages in the main sub-protocol is optimal when exchanging idempotent items using non-trusted devices. It is straightforward that when using trusted devices for exchanging nonidempotent items this number can be reduced to three. This however comes at the co...