Fairness is less of a problem in the real world if people meet physically. But receipts play an important role there as well (e.g., think of registered mail). On the Internet, fairness requires a different approach because the party who gets the item first can always cheat and run away!
Fairness in the on-line world can be ensured by a trusted agent (e.g., a digital notary) which exchanges the two items; however, this is a costly approach because the notary must be involved for all transactions.
Our optimistic fair exchange protocols ensure that the notary is not needed if all participants are honest. It comes in only in case communication links break down or one party tries to cheat. Thus, the workload of the notary is smaller and therefore, the optimistic approach is more economical and scales much better.
We are implementing a prototype for certified electronic exchanges using the optimistic fair-exchange protocols. The software ensures that a given message or object can be received by the recipient only if the sender receives a receipt. It is implemented in Java and can be integrated in standard e-mail clients and Web browsers.
Last modified : Saturday, 28 October 2000 14:36 CEST