An ambiguous optimistic fair exchange protocol with traceability

An Optimistic fair exchange (OFE) protocol is a protocol for fairly exchanging items between two parties. First in 2008, Huang et al. introduced the concept of ambiguous OFE in which the partial signature is ambiguous but the full one is not. Qu et al. in 2012, proposed a shceme with ambiguity for the full signature but not for the partial one. We solve the problem of both schemes by proposing the first efficient protocol that has ambiguity in both partial and full signature. Meanwhile, by using a traceable ring signature (TRS), we achieve the accountability property. We should highlight that our accountable OFE protocol is the first one secure in the standard model.