Theoretical Research Of Quantum Private Query Protocols

Classical cryptography is based on mathematical theory and Shannon’s secure communication theory.Its security depends on mathematical problems that are computationally complex and difficult to solve in polynomial time.But with the research of quantum computing and quantum computers,the security of classical cryptography has been severely challenged.At the same time the importance of quantum cryptography has been increasingly valued by all sectors of society.The security of quantum cryptography comes from the principles of quantum physics and it can theoretically achieve unconditional security,so it has attracted the attention of many researchers.So far,quantum cryptography has derived important branches such as quantum key distribution,quantum secret sharing,quantum secure direct communication,quantum inadvertent transmission,quantum bit commitment,quantum private query,quantum signature,and quantum key negotiation.Quantum private query(abbreviated as QPQ)is a quantum solution for symmetrically private information retrieval(abbreviated as SPIR).The aim of QPQ is to solve the private query problem between the user and the database owner,that is,to protect the security of both parties involved in the protocol while completing the query.With the rapid development of quantum technology,QPQ plays an increasingly important role in military,commercial,information retrieval and many other fields.But the scarcity of quantum resources,the defects of quantum devices and various attack methods are emerging,which makes it is especially important to research more secure,efficient and practical QPQ protocols.Aiming at the shortcomings of the existing QPQ protocols,this dissertation proposes an improved classical post-processing algorithm,a semi-device independent QPQ protocol and a continuous QPQ protocol.The main fruits are as follows:(1)Aiming at the shortcomings of the existing d-dimensional QPQ protocol,this dissertation proposes a novel classical post-processing(abbreviated as CPP)algorithm,which lifts the dimensional limitation on the amount of information that a user can obtain in a single query.And a new encoding method is used in our protocol,which reduces the requirement for the database owner Bob’s quantum capabilities,thereby improving the efficiency and practicability of the protocol.(2)This dissertation proposes a novel semi-device-independent QPQ protocol.The protocol uses the idea of two-dimensional quantum witness violation to protect the security of the database,while only assuming that the dimensions of the quantum system used in the protocol are bounded.Compared with the existing entangled device-independent QPQ protocol,this protocol is based on the“preparation-measurement” mode and does not use entangled states,so it’s easier to test and implement.(3)This dissertation proposes a continuous variable QPQ protocol.Existing protocols are mostly based on discrete variables,but perfect single photon is difficult to prepare in practical environments,so the security of the protocols is inevitably affected.Our protocol uses the coherent state as a carrier to improve the original original QPQ protocol based on discrete variables,while maintaining its performance and improving the efficiency and usability of the protocol.At the same time,the dissertation performs a security analysis on the proposed protocol to prove that it can well protect user privacy and database privacy.