Ambiguous Optimistic Fair Exchange
Optimistic fair exchange (OFE) is a protocol for solving the problem of exchanging items or services in a fair manner between two parties, a signer and a verifier, with the help of an arbitrator which is called in only when a dispute happens between the two parties. In almost all the previous work on OFE, after obtaining a partial signature from the signer, the verifier can present it to others and show that the signer has indeed committed itself to something corresponding to the partial signature even prior to the completion of the transaction. In some scenarios, this capability given to the verifier may be harmful to the signer. In this paper, we propose the notion of ambiguous optimistic fair exchange (A-OFE), which is an OFE but also requires that the verifier cannot convince anybody about the authorship of a partial signature generated by the signer. We present a formal security model for A-OFE in the multi-user setting and chosen-key model. We also propose an efficient construction with security proven without relying on the random oracle assumption.
KeywordsResolution Ambiguity Random Oracle Random Oracle Model Full Signature Sign Ambiguity
- 5.Bellare, M., Rogaway, P.: Random oracles are practical: A paradigm for designing efficient protocols. In: ACM CCS, pp. 62–73. ACM, New York (1993)Google Scholar
- 13.Dodis, Y., Reyzin, L.: Breaking and repairing optimistic fair exchange from PODC 2003. In: DRM 2003, pp. 47–54. ACM, New York (2003)Google Scholar
- 21.Kremer, S.: Formal Analysis of Optimistic Fair Exchange Protocols. PhD thesis, Université Libre de Bruxelles (2003)Google Scholar
- 23.Micali, S.: Simple and fast optimistic protocols for fair electronic exchange. In: PODC 2003, pp. 12–19. ACM, New York (2003)Google Scholar
- 24.Park, J.M., Chong, E.K., Siegel, H.J.: Constructing fair-exchange protocols for e-commerce via distributed computation of RSA signatures. In: PODC 2003, pp. 172–181. ACM, New York (2003)Google Scholar