1sharif University of Technology, electrical Engineering
2Sharif University of Technology
3Sharif University of Technology, electrical Engineering
In this paper we present an optimistic fair exchange (OFE) protocol for proxy signatures. This protocol is useful in scenarios that a signer cannot participate in an OFE protocol himself and he needs to delegate his signing power to another one. We give a new security model for this type of protocols because the best and the most complete model until now does not consider all security aspects of this protocol. We construct a generic scheme and give a paradigm for it. Our scheme is setup-free and multi-user secure in the random oracle and chosen-key model.