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### Paper:

TR01-050 | 24th June 2001 00:00

#### Black-Box Concurrent Zero-Knowledge Requires $\tilde\Omega(\log n)$ Rounds

TR01-050
Authors: Ran Canetti, Joe Kilian, Erez Petrank, Alon Rosen
Publication: 13th July 2001 15:48
Keywords:

Abstract:

We show that any concurrent zero-knowledge protocol for a non-trivial
language (i.e., for a language outside $\BPP$), whose security is proven
via black-box simulation, must use at least $\tilde\Omega(\log n)$
rounds of interaction. This result achieves a substantial improvement
over previous lower bounds, and is the first bound to rule out the
possibility of constant-round concurrent zero-knowledge when proven via
black-box simulation. Furthermore, the bound is polynomially related to
the number of rounds in the best known concurrent zero-knowledge
protocol for languages in $\NP$.

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