Darmstadt University of Technology
Deptartment of Computer Science
D-64283 Darmstadt, Germany

Recently, research has focused on enabling fair exchange between payment and electronically shipped items. The reason for this is the growing importance of Electronic Commerce and the increasing number of applications in this area. Although a considerable number of fair exchange protocols exist, they usually have been defined for special scenarios and thus only work under particular assumptions. Furthermore, these protocols provide different degrees of fairness and cause different communication overhead.

The purpose of this paper is to present a unifying solution to the problem. We do this by defining a suite of protocol modules which allow to compose protocols where the achieved degree of fairness can be enhanced step by step. The advantage of the stepwise approach is that after each step one can decide if the provided degree of fairness is acceptable or if one is willing to spend more in order to reach a higher degree of fairness. We show the applicability of our approach by deriving a novel efficient fair exchange protocol.