Non-black-box Simulation in the Fully Concurrent Setting, Revisited

We give a new proof of the existence of $$O(n^{\epsilon })$$O(n∈)-round public-coin concurrent zero-knowledge arguments for $$\mathcal {NP}$$NP, where $$\epsilon >0$$∈>0 is an arbitrary constant. The security is proven in the plain model under the assumption that collision-resistant hash functions exist. The existence of such concurrent zero-knowledge arguments was previously proven by Goyal (STOC'13) in the plain model under the same assumption. In the proof, we use a new variant of the non-black-box simulation technique of Barak (FOCS'01). An important property of our simulation technique is that the simulator runs in a "straight-line" manner in the fully concurrent setting. Compared with the simulation technique of Goyal, which also has such a property, the analysis of our simulation technique is (arguably) simpler.