On Pseudorandom Generators with Linear Stretch in NC0

  • Authors:
  • Benny Applebaum;Yuval Ishai;Eyal Kushilevitz

  • Affiliations:
  • Department of Computer Science, Princeton University, Princeton, USA 08540-5233;Computer Science Department, Technion Israel Institute of Technology, Technion City, Haifa, Israel 32000;Computer Science Department, Technion Israel Institute of Technology, Technion City, Haifa, Israel 32000

  • Venue:
  • Computational Complexity
  • Year:
  • 2008

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Abstract

We consider the question of constructing cryptographic pseudorandom generators (PRGs) in NC0, namely ones in which each bit of the output depends on just a constant number of input bits. Previous constructions of such PRGs were limited to stretching a seed of n bits to n +驴o(n) bits. This leaves open the existence of a PRG with a linear (let alone superlinear) stretch in NC0. In this work we study this question and obtain the following main results: We show that the existence of a linear-stretch PRG in NC0驴implies non-trivial hardness of approximation results without relying on PCP machinery. In particular, it implies that Max3SAT is hard to approximate to within some multiplicative constant. We construct a linear-stretch PRG in NC0驴under a specific intractability assumption related to the hardness of decoding "sparsely generated" linear codes. Such an assumption was previously conjectured by Alekhnovich (FOCS 2003).