Fourth International Network Conference, University of Plymouth, pp. 327-335, 2004.
Certified email is a value-added service of ordinary email, in which a sender wants to obtain a receipt from a recipient. Fair exchange protocols are a key component for certified email service to ensure fairness, i.e., the items held by two parties are exchanged without one party obtaining an advantage. We can find in the literature simple and fast optimistic protocols for fair electronic exchange and, more specifically, for certified electronic mail (CEM) and electronic contract signing (ECS). We have observed that some aspects of those protocols could be substantially improved. This paper presents two major contributions. Firstly, we provide a solution that allows both parties to end the protocol timely in an asynchronous way. Then, we extend the certified email service to the multicast scenario.