Editing (Symmetric) Private Information Retrieval (section)

===Security definitions===
(Quantum) private information retrieval protocols are said to be secure if they satisfy the following conditions:
*'''Correctness''': assuming that all the parties in the protocol are honest, then the output of the protocol on the user’s side must be the queried database element.
*'''User privacy''': assuming that the user is honest, then, throughout the protocol, any query of the user to a server leaks no information about the desired database item.
In addition to the above requirements, symmetric (quantum) private information retrieval protocols must also satisfy the following condition:
*'''Data(base) privacy''': assuming that the server(s) is (are) honest(s), then, throughout the protocol, the user is unable to obtain any information beyond a single database element.