An Optimistic Fair Exchange Protocol for Trading Electronic Rights

Reliable electronic commerce systems must offer fairness. In this paper, we propose a fair exchange protocol for trading electronic vouchers, which are the representation of rights to claim goods or services. This protocol enables two players to exchange vouchers stored in their smartcards fairly and efficiently. The players can exchange vouchers through a 4-round mutual communication protocol between their smartcards as long as the protocol is performed properly. If the protocol becomes unable to proceed due to misbehavior of the partner or for any other reason, the player that has fallen into the unfair condition (i.e. the player who sent its voucher but didn’t receive the desired voucher) can recover fairness by performing a recovery protocol with a trusted third-party. Since the recovery protocol doesn’t need the cooperation of the partner, fairness can be recovered without identifying or tracking the partner; one can trade vouchers securely even if the trading partner cannot be identified.