A gradual and optimistic fair exchange protocol

For electronic items without generability or revocability, previous optimistic exchange protocols can't guarantee strong fairness. Gradual protocols assume equal computing power. And online-TTP (Third Trusted Party) protocols often suffer from communication bottle-neck. A gradual and optimistic fair exchange protocol is presented in this paper to solve the problem. Secrets are gradually exchanged with partially validation by recipients, while the probability of detecting cheats increases. Fairness doesn't depend on equal computational power assumption. TTP isn't involved unless dispute appears. The protocol provides stronger fairness than optimistic or gradual schemes.