Towards proving strong direct product theorems

  • Authors:
  • Ronen Shaltiel

  • Affiliations:
  • Department of Applied Mathematics and Computer Science, Weizmann Institute of Science, Rehovot, 76100, Israel

  • Venue:
  • Computational Complexity
  • Year:
  • 2004

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Abstract

A fundamental question of complexity theory is the direct product question. A famous example is Yao's XOR-lemma, in which one assumes that some function f is hard on average for small circuits (meaning that every circuit of some fixed size s which attempts to compute f is wrong on a non-negligible fraction of the inputs) and concludes that every circuit of size s' only has a small advantage over guessing randomly when computing f⊕k(x1,...,xk) = f(x1) ⊕...⊕ f(xk) on independently chosen x1,...,xk. All known proofs of this lemma have the property that s' s. In words, the circuit which attempts to compute f⊕k is smaller than the circuit which attempts to compute f on a single input! This paper addresses the issue of proving strong direct product assertions, that is, ones in which s' ≈ ks and is in particular larger than s. We study the question of proving strong direct product question for decision trees and communication protocols.