Trading Static for Adaptive Security in Universally Composable Zero-Knowledge
- 979 Downloads
Adaptive security, while more realistic as an adversarial model, is typically much harder to achieve compared to static security in cryptographic protocol design. Universal composition (UC) provides a very attractive framework for the modular design of cryptographic protocols that captures both static and adaptive security formulations. In the UC framework, one can design protocols in hybrid worlds that allow access to idealized functionalities and then apply the universal composition theorem to obtain more concrete protocol instances. The zero-knowledge (ZK) ideal functionality is one of the most useful sub-protocols in modular cryptographic design. Given an adaptively secure protocol in the ideal ZK-hybrid-world do we always need an adaptively secure realization of the ZK functionality in order to preserve adaptive security under composition? In this work, perhaps surprisingly, we find that this is not so and in fact there are useful protocol instances that we can “trade static security for adaptive security.”
We investigate the above setting, by introducing a weakened ZK ideal functionality, called the ideal leaking-zero-knowledge functionality (LZK) that leaks some information about the witness to the adversary in a certain prescribed way. We show that while LZK is interchangeable to ZK against static adversaries, ZK is more stringent when adaptive adversaries are considered. We then proceed to characterize a class of protocols in the hybrid-ZK-world that can be “transported” to the LZK-hybrid-world without forfeiting their security against adaptive adversaries. Our results demonstrate that in such settings a static protocol realization of ZK is sufficient for ensuring adaptive security for the parent hybrid protocol something that enables simplified and substantially more efficient UC realizations of such protocols.
KeywordsStatic Security Ideal Functionality Cryptographic Protocol Commitment Scheme Cryptology ePrint Archive
Unable to display preview. Download preview PDF.
- 1.Barak, B., Canetti, R., Nielsen, J.B., Pass, R.: Universally composable protocols with relaxed set-up assumptions. In: FOCS 2004, pp. 186–195 (2004)Google Scholar
- 3.Canetti, R.: Universally composable security: A new paradigm for cryptographic protocols. In: FOCS 2001, pp. 136–145 (2001)Google Scholar
- 4.Canetti, R.: Universally composable signature, certification, and authentication. In: CSFW 2004, pp. 219–235 (2004), http://eprint.iacr.org/2003/239/
- 5.Canetti, R.: Universally composable security: A new paradigm for cryptographic protocols. In: Cryptology ePrint Archive: Report 2000/067 (December 2005), Latest version at http://eprint.iacr.org/2000/067/
- 9.Canetti, R., Lindell, Y., Ostrovsky, R., Sahai, A.: Universally composable two-party and multi-party secure computation. In: STOC 2002, pp. 494–503, http://www.cs.biu.ac.il/~lindell/PAPERS/uc-comp.ps
- 12.Goldreich, O., Micali, S., Wigderson, A.: How to play any mental game or A completeness theorem for protocols with honest majority. In: STOC 1987, pp. 218–229 (1987)Google Scholar
- 13.Kiayias, A., Zhou, H.-S.: Equivocal blind signatures and adaptive UC-security. In: Cryptology ePrint Archive: Report 2007/132 (2007)Google Scholar
- 14.Nielsen, J.B.: On protocol security in the cryptographic model. Dissertation Series DS-03-8, BRICS (2003), http://www.brics.dk/DS/03/8/BRICS-DS-03-8.pdf
- 15.Prabhakaran, M., Sahai, A.: Relaxing environmental security: Monitored functionalities and client-server computation. In: Kilian, J. (ed.) TCC 2005. LNCS, vol. 3378, pp. 104–127. Springer, Heidelberg (2005)Google Scholar