Adaptively Secure Constrained Pseudorandom Functions.
Dennis Hofheinz, Akshay Kamath, Venkata Koppula, Brent R. Waters · 2014
A constrained pseudo random function (PRF) behaves like a standard PRF, but with the added feature that the (master) secret key holder, having secret key K, can produce a constrained key, Kf, that allows for the evaluation of the PRF on a subset of the domain as determined by a predicate function f within some family F. While previous constructions gave constrained PRFs for poly-sized circuits, all reductions for such functionality were based in the selective model of security where an attacker declares which point he is attacking before seeing any constrained keys. In this paper we give new constrained PRF constructions for circuits that have polynomial reductions to indistinguishability obfuscation in the random oracle model. Our solution is constructed from two recently emerged primitives: an adaptively secure Attribute-Based Encryption (ABE) for circuits and a Universal Parameters as introduced by Hofheinz et al. Both primitives are constructible from indistin-guishability obfuscation (iO) (and injective pseudorandom generators) with only polynomial loss.