Supporting Fair Exchange in Mobile Environments

Mobile commerce over the Internet always includes the exchange of electronic goods. Fair exchange protocols establish fairness and ensure that both participants can engage in the exchange without the risk of suffering a disadvantage (e.g., losing their money without receiving anything for it). In general, fair exchange protocols require the continuous availability of an external trusted third party (TTP), a dedicated site which is trusted by both participants. Implementations of TTPs for fair exchange have been proposed to be based on carefully secured Internet hosts in order to establish trust. In this paper we present solutions to the fair exchange problem in mobile environments, where customers frequently disconnect from the network and thus continuous availability of the external TTP is not given. Our approach utilizes tamper-poof hardware on the customer's side partly taking over the duties of the TTP. Besides supporting disconnected operations our approach also allows the proper handling of time-sensitive items (i.e., items which lose value over time), a feature which previous protocols lack.