Adaptively Secure Constrained Pseudorandom Functions

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, K-f, 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 arbitrary circuits in the random oracle model based on indistinguishability obfuscation. Our solution is constructed from two recently emerged primitives: an adaptively secure Attribute-Based Encryption (ABE) for circuits and a Universal Sampler Scheme as introduced by Hofheinz et al. Both primitives are constructible from indistinguishability obfuscation (iO) (and injective pseudorandom generators) with only polynomial loss.