### Constant-Round Concurrent Non-Malleable Commitments and Decommitments

Rafail Ostrovsky, Giuseppe Persiano, and Ivan Visconti

##### Abstract

In this paper we consider commitment schemes that are secure against concurrent poly-time man-in-the-middle (cMiM) attacks. Under such attacks, two possible notions of security for commitment schemes have been proposed in the literature: concurrent non-malleability with respect to commitment and concurrent non-malleability with respect to decommitment (i.e., opening). After the original notion of non-malleability introduced by [Dolev, Dwork and Naor STOC 91] that is based on the independence of the committed and decommitted message, a new and stronger notion of non-malleability has been given in [Pass and Rosen STOC 05] by requiring that for any man-in-the-middle adversary there is a stand-alone adversary that succeeds with the same probability. Under this stronger security notion, a constant-round commitment scheme that is concurrent non-malleable only with respect to commitment has been given in [Pass and Rosen FOCS 05] for the plain model, thus leaving as an open problem the construction of a constant-round concurrent non-malleable commitments with respect to decommitment. In other words, in [Pass and Rosen FOCS 05] security against adversaries that mount concurrent man-in-the-middle attacks is guaranteed only during the commitment phase (under their stronger notion of non-malleability). The main result of this paper is a commitment scheme that is concurrent non-malleable with respect to both commitment and decommitment, under the stronger notion of [Pass and Rosen STOC 05]. This property protects against cMiM attacks mounted during both commitments and decommitments which is a crucial security requirement in several applications, as in some digital auctions, in which players have to perform both commitments and decommitments. Our scheme uses a constant number of rounds of interaction in the plain model and is the first scheme that enjoys all these properties under the definitions of [Pass and Rosen FOCS 05]. We stress that, exactly as in [Pass and Rosen FOCS 05], we assume that commitments and decommitments are performed in two distinct phases that do not overlap in time.

Available format(s)
Category
Foundations
Publication info
Published elsewhere. Unknown where it was published
Keywords
commitmentsdefinitionsnon-malleabilityconcurrency
Contact author(s)
visconti @ dia unisa it
History
Short URL
https://ia.cr/2008/235

CC BY

BibTeX

@misc{cryptoeprint:2008/235,
author = {Rafail Ostrovsky and Giuseppe Persiano and Ivan Visconti},
title = {Constant-Round Concurrent Non-Malleable Commitments and Decommitments},
howpublished = {Cryptology ePrint Archive, Paper 2008/235},
year = {2008},
note = {\url{https://eprint.iacr.org/2008/235}},
url = {https://eprint.iacr.org/2008/235}
}

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