Using Smart Cards for Fair Exchange

Abstract

Fair exchange protocols ensure that the participating parties, customer and vendor, can engage in electronic commerce transactions without the risk of suffering a disadvantage. This means that neither of them delivers his digital item without receiving the other party’s item. In general, fair exchange cannot be solved without the help of a trusted third party (TTP), a dedicated computer which is trusted by both participants. Trust can be established by carefully securing the TTP or even better by introducing tamper-proof hardware. However, if the communication to the TTP is unreliable or disrupted, then the exchange cannot be performed in a timely fashion or not at all. Up to now, this has been a problem especially for the exchange of time-sensitive items, i.e., items which lose value over time. We present a novel approach to perform fair exchange using tamper-poof hardware on the customer’s side. More specifically, co-located to the customer’s machine we use a smart card which partially takes over the role of the TTP. The challenge of designing protocols in this environment lies in the fact that the communication between the smart card and the vendor is under control of the customer. Our approach has the following benefits: It supports the exchange in mobile environments where customers frequently experience a disconnection from the network. Furthermore, our approach is the first to handle time-sensitive items properly.

This author’s work was supported by the Deutsche Forschungsgemeinschaft (DFG) as part of the PhD program (Graduiertenkolleg) “Enabling Technologies for Electronic Commerce” at Darmstadt University of Technology.