Private information retrieval

We describe schemes that enable a user to access k replicated copies of a database (k⩾2) and privately retrieve information stored in the database. This means that each individual database gets no information on the identity of the item retrieved by the user. For a single database, achieving this type of privacy requires communicating the whole database, or n bits (where n is the number of bits in the database). Our schemes use the replication to gain substantial saving. In particular, we have: A two database scheme with communication complexity of O(n^1/3). A scheme for a constant number, k, of databases with communication complexity O(n¹k/). A scheme for 1/3 log₂ n databases with polylogarithmic (in n) communication complexity