Optimally-Fair Exchange of Secrets via Delay Encryption and Commutative Blinding

We propose a new fair exchange protocol that takes advantage of delay encryption and commutative encryption to achieve optimal partial fairness among all protocols involving one-way messages. Our protocol consists of 3 setup messages and \(2N+1\) exchange messages and it is fair against covert adversaries with probability \(1- \frac{1}{2N}\) . We prove that this is optimal up to shortening the setup phase which is notably more efficient than existing protocols.