Fair Exchange Signature Schemes

In this paper we propose an efficient Fair Exchange Signature Scheme(FESS) that allows two players to exchange digital signatures in a fair way. It may be considered as an interesting extension of concurrent signature presented in EURO CRYPT 2004 that is constructed from ring signatures. In our scheme, two unwakened signatures signed separately by two participants can be verified easily by the other 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 revealed, two signatures are both aroused and become effective. A key feature of the proposed scheme is that two players can exchange digital signatures simultaneously through a secret commitment keystone without involvement of any Trusted Third Party. Moreover, the efficiency of our signature scheme is higher than that of concurrent signature.