Editing (Symmetric) Private Information Retrieval (section)

====Single-database protocols====
As in the classical setting, in the case of the database being owned by a ''single'' server, the trivial solution (downloading the whole database) is the only way to achieve information-theoretically secure PIR – even in the case of a specious (may deviate from the protocol if its malicious operations are unknown to the user) server [[#References|[2]]]. <br>
As for (quantum or classical) SPIR, it is impossible to achieve information-theoretic security with a single-server; this result was proved in the quantum setting by Lo [[#References|[3]]]. Intuitively, this comes from the fact that the (unique) trivial solution of information-theoretically secure PIR is the worst in terms of data privacy. Therefore, to design efficient PIR protocols or to achieve SPIR, several assumptions have been considered; they include:
* Hardness assumptions: PIR protocols with computational security.
* Assumptions on the adversarial model:
** to achieve SPIR: cheat-sensitive protocols (also known as quantum private queries (QPQ) protocols) where it is assumed that the server will not cheat if there is a non-zero probability that he will be caught cheating. 
***[[Quantum Private Queries Protocol Based on Quantum Oblivious Key Distribution|QPQ protocols based on quantum oblivious key distribution]]
***[[Quantum Private Queries Protocol Based on Quantum Random Access Memory|QPQ protocols based on quantum random access memory]]
** to achieve efficient PIR: assuming an honest server.
***[[Single-Database Quantum Private Information Retrieval in the Honest Server Model|QPIR protocols in the honest server model]]
* Prior shared entanglement between server and user: in the honest server model, efficient PIR protocols exist, however for a specious or malicious server, the trivial solution is optimal for PIR[[#References|[4]]].
**[[Single-Database Quantum Private Information Retrieval with Prior Shared Entanglement in the Honest Server Model|QPIR protocols with prior shared entanglement in the honest server model]]
* Relativistic assumptions: quantum SPIR protocols whose security uses properties from special relativity.
**[[Relativistic Quantum Oblivious Transfer|Relativistic QOT protocols]]