Date Added: Feb 2011
Security services become crucial to many applications such as e-commerce payment protocols, electronic contract signing, and certified e-mail delivery, with the phenomenal growth of the Internet and open networks. For these applications fair exchange must be assured. A fair protocol allows two parties to exchange digital signatures over the Internet in a fair way, so that either each party gets the other's signature, or neither party does. This paper, gives a survey on the most important fair and optimistic digital signature exchange protocols. Optimistic, means the Third Trusted Party (TTP) is involved only in the situations where one party is cheating or the communication channel is interrupted, i.e., TTP is offline.