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Global Mobile Congress

An optimistic fair exchange protocol based on committed signature

Guanghui Chen, Sihan Qing, Zhifeng Qi, Yixian Yang

Published Oct 1, 2009• 1 citation
Publisher

Abstract

A verifiable committed signature is constructed based on Fischlin's signature scheme and is proved of its security in the standard complexity model. And then, an optimistic fair exchange protocol with punishment function is designed based on the committed signature. It will punish the misbehavior of either party in order to ensure the fairness of the exchange. Through the analysis, not only are some properties of the exchange, such as fairness, timeliness, abuse-free etc, ensured better, but also because of the introduction of punishment idea, both parties' behavior is confined better, which makes the protocol fairer, simpler and more efficient.

DOI
10.1109/gmc.2009.5295876

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A verifiable committed signature is constructed based on Fischlin's signature scheme and is proved of its security in the standard complexity model. And then, an optimistic fair exchange protocol with punishment function is designed based on the committed signature. It will punish the misbehavior of either party in order to ensure the fairness of the exchange. Through the analysis, not only are some properties of the exchange, such as fairness, timeliness, abuse-free etc, ensured better, but also because of the introduction of punishment idea, both parties' behavior is confined better, which makes the protocol fairer, simpler and more efficient.
In PODC 2003, Park et al. [32] first introduce a connection between fair exchange and sequential two-party multi-signature scheme and provide a novel method of constructing fair exchange protocol by distributing the computation of RSA signature. This approach avoids the design of verifiable encryption scheme at the expense of having cosigner store a piece of prime signer's secret key. Dodis and Reyzin [20] showed that the protocol in [32] is totally breakable in the registration phase, then presented a remedy scheme which is provably secure in the random oracle model, by utilizing Boldyreva non-interactive two-party multi-signature scheme [8]. Security in the random oracle model does not imply security in the real world. In this paper, we provide the first two e#cient committed signatures which are provably secure in the standard complexity model from strong RSA assumption. Then we construct e#cient optimistic fair exchange protocols from those new primitives.
In CIS2008, Gao et al. suggested an abuse-free optimistic fair exchange protocol based on the short signature. Their scheme is very efficient in terms of communication. In this paper, we point out that their scheme has two weaknesses. These weaknesses may lead to an unfair situation that Bob may obtain Alice's signature, but Alice can not obtain Bob's signature. In order to overcome these weaknesses, we propose a new secure abuse-free optimistic fair exchange protocol. In the new protocol, both parties can contact the trusted third party and settle the argument before the deadline. Moreover, we give a formal proof of fairness in the strand space model.
Fairness is the basic requirement of E-Commerce protocols. RSA is one of the most widely used cryptosystems. A fair-exchange protocol allows two parties to exchange items in a fair way so that either each party gets the other's item, or neither party does. In this paper construction and architecture of the existing fair exchange protocols are analyzed. Both practicality and efficiency problems of these protocols are also presented. Based on this analysis, an optimistic fair exchange protocol totally based on RSA signature scheme is proposed. The novel scheme employs verifiably encrypted RSA signatures in the extended integer ring that is elaborately constructed. The security and efficiency of the newly devised scheme are also proved and examined. It is showed that the proposed scheme is secure and efficient.
A fair exchange scheme is a protocol by which two parties Alice and Bob swap items or services without allowing either party to gain an advantage by quitting prematurely or otherwise misbehaving. Verifiably committed signature is a generalized and unified model for non-interactive optimistic fair exchange scheme. The state-of-the-art verifiably committed signature that enjoys the off-line, setup-free and stand-alone properties is due to Zhu and Bao [1]. In this article, we show that the Zhu-Bao's verifiably committed signature is insecure in the multi-user setting and then consider possible countermeasures.
A fair contract-signing protocol allows two potentially mistrusted parities to exchange their commitments (i.e., digital signatures) to an agreed contract over the Internet in afairway, so that either each of them obtains the other's signature, or neither party does. Based on the RSA signature scheme, a new digital contract-signing protocol is proposed in this paper. Like the existing RSA-based solutions for the same problem, our protocol is not only fair, but also optimistic, since the trusted third party is involved only in the situations where one party is cheating or the communication channel is interrupted. Furthermore, the proposed protocol satisfies a new property-abuse-freeness. That is, if the protocol is executed unsuccessfully, none of the two parties can show the validity of intermediate results to others. Technical details are provided to analyze the security and performance of the proposed protocol. In summary, we present the first abuse-free fair contract-signing protocol based on the RSA signature, and show that it is both secure and efficient.