**
Four-Round Concurrent Non-Malleable Commitments from One-Way Functions**

*
Michele Ciampi, Rafail Ostrovsky, Luisa Siniscalchi, Ivan Visconti
*

How many rounds and which assumptions are required for * concurrent * non-malleable commitments?
The above question has *puzzled* researchers for several years. Pass in [TCC 2013]shoed a lower bound
of 3 rounds for the case of black-box reductions to falsifiable hardness assumptions with respect
to polynomial-time adversaries. On the other side, Goyal [STOC 2011], Lin and Pass[STOC 2011] and Goyal et al.
[FOCS 2012] showed that one -way functions (OWFs) are sufficient with a constant number of rounds. More recently Ciampi et al.
[CRYPTO 2016]showed a 3-round construction based on sub exponentially strong one-way permutations.

In this work we show * as main result * the first 4-round concurrent non-malleable commitment scheme assuming the existence of any one -way function.

Our approach builds on a new security notion for argument systems against man-in-the-middle attacks: * Simulation-Witness-Independence *.
We show how to construct a 4-round one-manysimulation-witnesses-independent argument system
from one-way functions. We then combine this new tool in parallel with a weak form of non-malleable commitments constructed by Goyal et al. in [FOCS 2014] obtaining the main result of out work.
**comment:**
CRYPTO (2) 2017: 127-157

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