Another Look at Extended Private Information Retrieval Protocols

Extended Private Information Retrieval (EPIR) has been introduced at CANS'07 by Bringer et al. as a generalization of the notion of Private Information Retrieval (PIR). The principle is to enable a user to privately evaluate a fixed and public function with two inputs, a chosen block from a database and an additional string. The main contribution of our work is to extend this notion in order to add more flexibility during the system life. As an example, we introduce a general protocol enabling polynomial evaluations. We also revisit the protocol for Hamming distance computation which was described at CANS'07 to obtain a simpler construction. As to practical concern, we explain how amortizing database computations when dealing with several requests.