Fair electronic exchange with virtual trusted parties

Abstract

Assume each of two parties has something the other wants. Then, a Fair exchange is an electronic protocol guaranteeing that either both parties get what they want, or none of them does. Protocols relying on traditional trusted parties easily guarantee such exchanges, but are inefficient and expensive, because a trusted party must be part of (thus be paid for) every execution. We put forward a new class of protocols, relying on virtual trusted parties (a new type of trusted party), and show that they provide Fair exchange more efficiently than before, and at a fraction of the cost. In particular, we provide attractive protocols for Fair certified e-mail and contract signing.