Benny Applebaum TITLE: Basing Lower-Bounds for Learning on Worst-Case Assumptions ABSTRACT: We consider the question of whether P \neq NP implies that there exists some concept class that is efficiently representable but is still hard to learn in the PAC model of Valiant (CACM '84). We show that unless the Polynomial Hierarchy collapses, such a statement cannot be proven via a large class of reductions including Karp reductions, truth-table reductions, and a restricted form of non-adaptive Turing reductions. Also, a proof that uses a Turing reduction of constant levels of adaptivity would imply an important consequence in cryptography as it yields a transformation from any average-case hard problem in NP to a one-way function. Our results hold even in the stronger model of agnostic learning. These results are obtained by showing that lower bounds for improper learning are intimately related to the complexity of zero-knowledge arguments and to the existence of weak cryptographic primitives. In particular, we prove that if a language L reduces to the task of improper learning circuits, then, depending on the type of the reduction in use, either (1) L has a statistical zero-knowledge argument system, or (2) the worst-case hardness of L implies the existence of a weak variant of one-way functions defined by Ostrovsky-Wigderson (ISTCS '93). Interestingly, we observe that the converse implication also holds. Namely, if (1) or (2) hold then the intractability of L implies that improper learning is hard.