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The 43rd Annual IEEE Symposium on Foundations of Computer Science, 2002. Proceedings. (2002)
Vancouver, BC, Canada
Nov. 16, 2002 to Nov. 19, 2002
ISSN: 0272-5428
ISBN: 0-7695-1822-2
pp: 261
Amos Beimel , Ben-Gurion University
Yuval Ishai , Technion
Eyal Kushilevitz , Technion
Jean-François Raymond , McGill University
<p>Private Information Retrieval (PIR) protocols allow a user to retrieve a data item from a database while hiding the identity of the item being retrieved. Specifically, in information-theoretic, k-server PIR protocols the database is replicated among k servers, and each server learns nothing about the item the user retrieves. The cost of such protocols is measured by the communication complexity of retrieving one out of n bits of data. For any fixed k, the complexity of the best protocols prior to our work was 0(n^{\frac{1}{{2k - 1}}}) (Ambainis, 1997). Since then several methods were developed in an attempt to beat this bound, but all these methods yielded the same asymptotic bound.</p> <p>In this work, this barrier is finally broken and the complexity of information-theoretic k-server PIR is improved to n^{0(\frac{{\log \log k}}{{k\log k}})}. The new PIR protocols can also be used to construct k-query binary locally decodable codes of length exp (n^{0(\frac{{\log \log k}}{{k\log k}})}), compared to exp (n^{\frac{1}{{k - 1}}}) in previous constructions. The improvements presented in this paper apply even for small values of k: the PIR protocols are more efficient than previous ones for every k \geqslant 3, and the locally decodable codes are shorter for every k \geqslant 4.</p>

J. Raymond, Y. Ishai, A. Beimel and E. Kushilevitz, "Breaking the O(n<sup>1/(2k-1)</sup>) Barrier for Information-Theoretic Private Information Retrieval," The 43rd Annual IEEE Symposium on Foundations of Computer Science, 2002. Proceedings.(FOCS), Vancouver, BC, Canada, 2002, pp. 261.
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