Quantum Private Queries: Security Analysis

A security analysis of the recently introduced Quantum Private Query (QPQ) protocol is presented. The latter is a cheat sensitive quantum protocol to perform a private search on a classical database. It allows a user to retrieve an item from the database without revealing which item was retrieved, and at the same time it ensures data privacy of the database (the information that the user retrieves in a query is bounded). The security analysis is based on information-disturbance tradeoffs which show that whenever the provider tries to obtain information on the query, the query (encoded into a quantum system) is disturbed so that the person querying the database can detect the privacy violation. The security bounds are derived under the assumption that a unique answer corresponds to each query. To remove this assumption, some simple variants of the protocol are illustrated, and it is conjectured that analogous security bounds apply to them.