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Amos Beimel, Yuval Ishai, Eyal Kushilevitz, JeanFrançois Raymond, "Breaking the O(n<sup>1/(2k1)</sup>) Barrier for InformationTheoretic Private Information Retrieval," 2013 IEEE 54th Annual Symposium on Foundations of Computer Science, pp. 261, The 43rd Annual IEEE Symposium on Foundations of Computer Science (FOCS'02), 2002.  
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@article{ 10.1109/SFCS.2002.1181949, author = {Amos Beimel and Yuval Ishai and Eyal Kushilevitz and JeanFrançois Raymond}, title = {Breaking the O(n<sup>1/(2k1)</sup>) Barrier for InformationTheoretic Private Information Retrieval}, journal ={2013 IEEE 54th Annual Symposium on Foundations of Computer Science}, volume = {0}, year = {2002}, issn = {02725428}, pages = {261}, doi = {http://doi.ieeecomputersociety.org/10.1109/SFCS.2002.1181949}, publisher = {IEEE Computer Society}, address = {Los Alamitos, CA, USA}, }  
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TY  CONF JO  2013 IEEE 54th Annual Symposium on Foundations of Computer Science TI  Breaking the O(n<sup>1/(2k1)</sup>) Barrier for InformationTheoretic Private Information Retrieval SN  02725428 SP EP A1  Amos Beimel, A1  Yuval Ishai, A1  Eyal Kushilevitz, A1  JeanFrançois Raymond, PY  2002 KW  null VL  0 JA  2013 IEEE 54th Annual Symposium on Foundations of Computer Science ER   
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 informationtheoretic, kserver 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.
In this work, this barrier is finally broken and the complexity of informationtheoretic kserver PIR is improved to n^{0(\frac{{\log \log k}}{{k\log k}})}. The new PIR protocols can also be used to construct kquery 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.