Efficient Fair Exchange from Identity-Based Signature

Dae Hyun YUM  Pil Joong LEE  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E91-A   No.1   pp.119-126
Publication Date: 2008/01/01
Online ISSN: 1745-1337
DOI: 10.1093/ietfec/e91-a.1.119
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Cryptography and Information Security)
Category: Protocols
optimistic fair exchange,  contract signing,  identity-based signature,  

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A fair exchange scheme is a protocol by which two parties Alice and Bob exchange items or services without allowing either party to gain advantages by quitting prematurely or otherwise misbehaving. To this end, modern cryptographic solutions use a semi-trusted arbitrator who involves only in cases where one party attempts to cheat or simply crashes. We call such a fair exchange scheme optimistic. When no registration is required between the signer and the arbitrator, we say that the fair exchange scheme is setup-free. To date, the setup-free optimist fair exchange scheme under the standard RSA assumption was only possible from the generic construction of [12], which uses ring signatures. In this paper, we introduce a new setup-free optimistic fair exchange scheme under the standard RSA assumption. Our scheme uses the GQ identity-based signature and is more efficient than [12]. The construction can also be generalized by using various identity-based signature schemes. Our main technique is to allow each user to choose his (or her) own "random" public key in the identity-based signature scheme.