Privacy-preserving location-dependent query processing

A mobile portable device will often make queries, to a remote database, that depend on its location: It may ask for the nearest coffee shop, restaurant, pharmacy, etc. For privacy reasons, the mobile unit may not wish to disclose its precise location to the remote database - while it is unavoidable that the cell phone company already knows the rough location of the customer ("somewhere in Lafayette "), it is quite another matter if the customer\´s precise location can be tracked over tune through his pattern of location-dependent queries to the remote database. This work describes an efficient protocol, between the client and database, through which a client can learn the answer to its location-dependent query without revealing to the remote database anything about his location, other than what the database can infer from the answer it gives to the query (which is unavoidable). We also analyze the performance of some other, simpler solutions, that do not require the database to run a protocol with the client, but that can reveal more information about the private location and also introduce inaccuracies in the answer - we quantify how much error these simpler schemes introduce in the answer.