Private Constrained PRFs (and More) from LWE
In a constrained PRF, the owner of the PRF key K can generate constrained keys \(K_f\) that allow anyone to evaluate the PRF on inputs x that satisfy the predicate f (namely, where f(x) is “true”) but reveal no information about the PRF evaluation on the other inputs. A private constrained PRF goes further by requiring that the constrained key \(K_f\) hides the predicate f.