A traceable optimistic fair exchange protocol in the standard model

Abstract

An Optimistic Fair Exchange (OFE) protocol is a good way for two parties to exchange their digital items in a fair way such that at the end of the protocol execution, both of them receive their items or none of them receive anything. In an OFE protocol there is a semi-trusted third party, named arbitrator, which involves in the protocol if it is necessary. But there is a security problem when arbitrator acts dishonestly and colludes with the verifier, that is, the arbitrator can complete the transaction without getting signer's agreement. Huang <em>et al</em>. in 2011 addressed this issue by formalizing the accountability property. However, Huang <em>et al.</em>'s scheme is secure in the random oracle model which is not available in the real world. We present the first generic accountable OFE protocol that is secure in the standard model by using traceable ring signatures (TRSs) as our primitive. We prove the security of our protocol under the chosen-key model and multi-user setting.