Lower Bounds for Linear Locally Decodable Codes and Private Information Retrieval

  • Authors:
  • Oded Goldreich;Howard Karloff;Leonard J. Schulman;Luca Trevisan

  • Affiliations:
  • -;-;-;-

  • Venue:
  • CCC '02 Proceedings of the 17th IEEE Annual Conference on Computational Complexity
  • Year:
  • 2002

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Abstract

We prove that if a linear error-correcting code C:\{0,1\}^n\to\{0,1\}^m is such that a bit of the message can be probabilistically reconstructed by looking at two entries of a corrupted codeword, then m = 2^{\Omega(n)}. We also present several extensions of this result.We show a reduction from the complexity of one-round, information-theoretic Private Information Retrieval Systems (with two servers) to Locally Decodable Codes, and conclude that if all the servers' answers are linear combinations of the database content, then t = \Omega(n/2^a), where t is the length of the user's query and a is the length of the servers' answers. Actually, 2^a can be replaced by O(a^k), where k is the number of bit locations in the answer that are actually inspected in the reconstruction.