International Association
for Cryptologic Research

The notion of Zero Knowledge introduced by Goldwasser, Micali, and Rackoff in STOC 1985 is fundamental in Cryptography. Motivated by conceptual and practical reasons, this notion has been explored under stronger definitions. We will consider the following two main strengthened notions.

-- Statistical Zero Knowledge: here the zero-knowledge property will last forever, even in case in future the adversary will have unlimited power.

-- Concurrent Non-Malleable Zero Knowledge: here the zero-knowledge property is combined with non-transferability and the adversary fails in mounting a concurrent man-in-the-middle attack aiming at transferring zero-knowledge proofs/arguments.

Besides the well-known importance of both notions, it is still unknown whether one can design a zero-knowledge protocol that satisfies both notions simultaneously.

In this work we shed light on this question in a very strong sense. We show a {\\em statistical concurrent non-malleable} zero-knowledge argument system for NP with a {\\em black-box} simulator-extractor.