## CryptoDB

### Paper: How To Play Almost Any Mental Game Over The Net --- Concurrent Composition via Super-Polynomial Simulation

Authors: Boaz Barak Amit Sahai URL: http://eprint.iacr.org/2005/106 Search ePrint Search Google We construct a secure protocol for any multi-party functionality that remains secure (under a relaxed definition of security) when executed concurrently with multiple copies of itself and other protocols. We stress that we do *not* use any assumptions on existence of trusted parties, common reference string, honest majority or synchronicity of the network. The relaxation of security, introduced by Prabhakaran and Sahai (STOC '04), is obtained by allowing the ideal-model simulator to run in *quai-polynomial* (as opposed to polynomial) time. Quasi-polynomial simulation suffices to ensure security for most applications of multi-party computation. Furthermore, Lindell (FOCS '03, TCC' 04) recently showed that such a protocol is *impossible* to obtain under the more standard definition of *polynomial-time* simulation by an ideal adversary. Our construction is the first such protocol under reasonably standard cryptographic assumptions. That is, existence of a hash function collection that is collision resistent with respect to circuits of subexponential size, and existence of trapdoor permutations that are secure with respect to circuits of quasi-polynomial size. We introduce a new technique: protocol condensing''. That is, taking a protocol that has strong security properties but requires *super-polynomial* communication and computation, and then transforming it into a protocol with *polynomial* communication and computation, that still inherits the strong security properties of the original protocol. Our result is obtained by combining this technique with previous techniques of Canetti, Lindell, Ostrovsky, and Sahai (STOC '02) and Pass (STOC '04).
##### BibTeX
@misc{eprint-2005-12442,
title={How To Play Almost Any Mental Game Over The Net --- Concurrent Composition via Super-Polynomial Simulation},
booktitle={IACR Eprint archive},
keywords={Non-malleable protocols, concurrent composition, multi-party secure computation},
url={http://eprint.iacr.org/2005/106},
note={FOCS 2005 boaz@cs.princeton.edu 13021 received 10 Apr 2005, last revised 26 Aug 2005},
author={Boaz Barak and Amit Sahai},
year=2005
}