## Cryptology ePrint Archive: Report 2003/042

Timed Fair Exchange of Standard Signatures

Juan A. Garay and Carl Pomerance

Abstract: In this paper we show how to achieve timed fair exchange of digital signatures of standard type. Timed fair exchange (in particular, contract signing) has been considered before, but only for Rabin and RSA signatures of a special kind.

Our construction follows the gradual release paradigm, and works on a new time'' structure that we call a {\em mirrored time-line.} Using this structure, we design a protocol for the timed fair exchange by two parties of arbitrary values (values lying on their respective mirrored time-lines). Finally, we apply the blinding techniques of Garay and Jakobsson to turn this protocol into a protocol for the timed fair exchange of standard signatures.

The length of these mirrored time-lines makes another problem apparent, which is making sure that the underlying sequence has a period large enough so that cycling is not observed. We also show how to construct these structures so that, under reasonable assumptions, this is indeed the case.

Category / Keywords: cryptographic protocols /

Publication Info: Financial Crypto 2003

Date: received 3 Mar 2003, last revised 3 Mar 2003

Contact author: garay at research bell-labs com

Available format(s): Postscript (PS) | Compressed Postscript (PS.GZ) | BibTeX Citation

Short URL: ia.cr/2003/042

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