Title: An optimistic fair exchange protocol and its security in the universal composability framework

Authors: Yusuke Okada, Yoshifumi Manabe, Tatsuaki Okamoto

Addresses: Department of Social Informatics, Graduate School of Informatics, Kyoto University, Kyoto, Japan. ' NTT Communication Science Laboratories, Nippon Telegraph and Telephone Corporation; Department of Social Informatics,Graduate School of Informatics, Kyoto University, Kyto, Japan. ' NTT Information Sharing Platform Laboratories, Nippon Telegraph and Telephone Corporation; Department of Social Informatics, Graduate School of Informatics, Kyoto University, Kyto, Japan

Abstract: Fair exchange protocols allow both or neither of two parties to obtain the other|s items, and this property is essential in e-commerce. In this paper, we construct an optimistic fair exchange protocol that is applicable to any digital signature by prescribing three forms of signatures, namely presignature, post-signature and notarised signature. We set an expiration date for presignature, and thus realise the timely termination of the protocol. Next, we define an ideal functionality of fair exchange protocols in the universal composability framework. Then, we construct an optimistic fair exchange protocol based on the above protocol, and prove its security in the universal composability framework.

Keywords: fair exchange protocols; digital signatures; trusted third party; TTP; universal composition; applied cryptography; security; e-commerce; electronic commerce.

DOI: 10.1504/IJACT.2008.017052

International Journal of Applied Cryptography, 2008 Vol.1 No.1, pp.70 - 77

Available online: 06 Feb 2008 *

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