Fair exchange signature schemes

In this paper a new class of fair exchange signature scheme （FESS） is proposed that allows two players to exchange digital signatures in a fair way. The new signature scheme is a general model and has various implementations based on most of the existing signature schemes; thus it may also be considered as an interesting extension of concurrent signature presented in EUROCRYPT 2004 that is constructed from ring signatures. In FESS, two unwakened signatures signed respectively by two participants can be verified easily by each player, but it would not go into effect until an extra piece of commitment keystone is released by one of the players. Once the keystone is revealed, two signatures are both aroused and become valid. A key feature of FESS is that two players can exchange digital signatures simultaneously through a secret commitment keystone without involvement of any trusted third party （TTP）. Moreover, the efficiency of the new scheme is higher than that of concurrent signatures.