Timed Fair Exchange of Standard Signatures: [Extended 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 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.