Polylogarithmic two-round argument systems

We present a two-round argument system for NP languages with polylogarithmic communication complexity. We introduce a novel property of private information retrieval (PIR) schemes, that we call database-awareness. We construct a concrete database-aware PIR scheme and build our argument system by combining a database-aware PIR scheme with a probabilistically checkable proof system (PCP). Dwork et al. (2004) pointed out difficulties to prove the soundness of such constructions for arbitrary PIR schemes. But we show the restriction to database-aware PIR schemes is sufficient to overcome these difficulties.