computational complexity

, Volume 15, Issue 3, pp 263–296 | Cite as

Lower bounds for linear locally decodable codes and private information retrieval

  • Oded Goldreich
  • Howard Karloff
  • Leonard J. Schulman
  • Luca Trevisan


We prove that if a linear error-correcting code C:{0, 1} n →{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 = 2Ω (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  =  Ω (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.


Error-correcting codes lower bounds locally decodable codes private information retrieval 

Subject classification.



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Copyright information

© Birkhäuser Verlag, Basel 2006

Authors and Affiliations

  • Oded Goldreich
    • 1
  • Howard Karloff
    • 2
  • Leonard J. Schulman
    • 3
  • Luca Trevisan
    • 4
  1. 1.Computer Science DepartmentWeizmann Institute of ScienceRehovotIsrael
  2. 2.AT&T Labs–ResearchU.S.A.
  3. 3.Caltech, MC256-80PasadenaU.S.A.
  4. 4.Computer Science DivisionUniversity of California at BerkeleyBerkeleyU.S.A.

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