Deterministic Extractors for Bit-Fixing Sources by Obtaining an Independent Seed

  • Authors:
  • Ariel Gabizon;Ran Raz;Ronen Shaltiel

  • Affiliations:
  • Weizmann Institute;Weizmann Institute;Weizmann Institute

  • Venue:
  • FOCS '04 Proceedings of the 45th Annual IEEE Symposium on Foundations of Computer Science
  • Year:
  • 2004

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Abstract

An (n, k)-bit-fixing source is a distribution X over {0, 1}n such that there is a subset of k variables in X1, . . .,Xn which are uniformly distributed and independent of each other, and the remaining n - k variables are fixed. A deterministic bit-fixing source extractor is a function E : {0, 1}^n . {0, 1}^m which on an arbitrary (n, k)-bit-fixing source outputs m bits that are statistically-close to uniform. Recently, Kamp and Zuckerman [13] gave a construction of deterministic bit-fixing source extractor that extracts 驴(k虏/n) bits, and requires k \sqrt n. In this paper we give constructions of deterministic bit-fixing source extractors that extract (1 - o(1))k bits whenever k (log n)^c for some universal constant c 0. Thus, our constructions extract almost all the randomness from bit-fixing sources and work even when k is small. For k 驴 \sqrt n the extracted bits have statistical distance 2^{ - n^{\Omega (1)} } from uniform, and for k 驴 \sqrt n the extracted bits have statistical distance k^{ - \Omega (1)} from uniform. Our technique gives a general method to transform deterministic bit-fixing source extractors that extract few bits into extractors which extract almost all the bits.