Memory organization schemes for large shared data
STACS'99 Proceedings of the 16th annual conference on Theoretical aspects of computer science
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Private information retrieval (PIR) schemes provide a user with information from a database while keeping his query secret from the database manager. We propose a new model for PIR, utilizing auxiliary random servers providing privacy services for database access. The principal database initially engages in a preprocessing setup computation with the random servers, followed by the on-line stage with the users. Using this model we achieve the first PIR information theoretic solutions in which the database does not need to give away its data to be replicated, and with minimal on-line computation cost for the database. This solves privacy and efficiency problems inherent to all previous solutions. Specifically, in all previously existing PIR schemes the database on-line computation for one query is at least linear in the size of the data, and all previous information theoretic schemes require multiple replications of the database which are not allowed to communicate with each other. This poses a privacy problem for the database manager, who is required to hand his data to multiple foreign entities, and to the user, who is supposed to trust the multiple copies of the database not to communicate. In contrast, in our solutions no replication is needed, and the database manager only needs to perform O(1) amount of computation to answer questions of users, while all the extra computations required on line for privacy are done by the auxiliary random servers, who contain no informatin about the data.