1. An apparatus for delegating by a delegator evaluation of a pseudorandom function to a proxy, comprising: a memory; and at least one processing device, coupled to the memory, operative to: compute, using said at least one processing device, a trapdoor based on a secret key and a predicate, wherein said predicate defines a plurality of values for which the proxy is authorized to evaluate said pseudorandom function, wherein said plurality of values comprise a subset of a larger domain of values; and provide, using said at least one processing device, said trapdoor to said proxy for said proxy to evaluate said pseudorandom function on behalf of said delegator, wherein said trapdoor provides an indication to said proxy of said plurality of values for which the proxy is authorized to evaluate said pseudorandom function.