Functions with this property do not exist in Pessiland, the “worst of all possible worlds” according to Russell Impagliazzo’s “five worlds” paper. Miklós Ajtai names a family of functions proposed to have this property based on the short integer solution problem. A theorem that guarantees the existence of a hardcore predicate for every function with this property is named for Goldreich and Levin, who also proposed enumerating all computable Turing machines to construct a (*) “universal” function with this property. Modular squaring is part of a collection of functions thought to have this property named for Rabin, whose existence would imply that P ≠ NP. Multiplication has this property if factoring is “hard.” For 10 points, name this property possessed by functions ubiquitous in cryptography, which are easy to compute but difficult (-5[1])to invert. ■END■ (0[4])