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

Abstract

We give a new proof of the existence of O(n)-round public-coin concurrent zero-knowledge arguments for N P, where > 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.

Foundations of Programmable Secure Computation

“…The exact definition of plausible environments determines how and where the protocol can be used securely. Restrictions on the correspondence ρ define various flavours of black-box [39] and white-box security [40,41] or specify tightness requirements like polynomial and superpolynomial simulation [42,43]. Restrictions to A 1 and A 2 usually fix the model of corruption while constraints on E place restrictions on the protocol scheduling.…”