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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.
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Goldreich et al. (1989) studied this question.