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Original Article

Towards proving strong direct product theorems

Ronen ShaltielContact Information

(1) Department of Applied Mathematics and Computer Science, Weizmann Institute of Science, Rehovot, 76100, Israel

Received: 10 July 2003  

Abstract  A fundamental question of complexity theory is the direct product question. A famous example is Yaorsquos 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 srsquo only has a small advantage over guessing randomly when computing $$  f^{\bigoplus k}(x_{1},...,x_{k}) = f(x_{1})\bigoplus...\bigoplus f(x_{k}) $$ on independently chosen $$ x_{1},...,x_{k} $$ . All known proofs of this lemma have the property that srsquo < s . In words, the circuit which attempts to compute $$ f^{\bigoplus k} $$ 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 $$ s' \approx ks $$ and is in particular larger than s. We study the question of proving strong direct product question for decision trees and communication protocols.

Keywords.  Product theorems - XOR-lemma - hardness amplification - average case complexity

Mathematics Subject Classification (2000).  68Q17 - 68Q15


Contact InformationRonen Shaltiel
Email: ronens@wisdom.weizmann.ac.il
URL: http://www.wisdom.weizmann.ac.il/~ronens
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