Private Database Queries With a Quantum Third Party

It is of great importance to guarantee the privacy of the database and users when the database is being queried. A private database queries protocol based on a quantum Third Party (TP) is proposed by utilizing the quantum correlation of three-photon Greenberger-Horne-Zeilinger (GHZ) states. The proposed protocol is highly tolerant of channel loss and robust against fake entangled state attack and quantum memory attack implemented by the third party. With the help of the TP, the amount of private information obtained by the users from the database is deterministically controllable in the proposed protocol. Furthermore, the true tripartite entanglement witness by using Mermin-Bell inequality can ensure the security of the protocol, which expands the application area of Device-Independent (DI) entanglement witnesses.