Key points are not available for this paper at this time.
A central tool in constructing pseudorandom generators, secure encryption functions, and in other areas are “hard-core” predicates b of functions (permutations) ƒ, discovered in Blum Micali 82. Such b(x) cannot be efficiently guessed (substantially better than 50-50) given only ƒ(x). Both b, ƒ are computable in polynomial time.
Goldreich et al. (Sun,) studied this question.