Researches And Applications Of Quantum Information Coding In Quantum Cryptography

As we known, the security of most classical cryptography system is based on the computational hardness assumptions. With the rapid development of computing capacity and the proposition of variety of advanced algorithms, especially quantum computation, the classical cryptography is facing more and more serious threaten. Research shows that many existing cryptosystems will become no longer secure once quantum computer appears. Therefore, people begin to sturdy new technologies of cryptography which could resist the great threaten of quantum computation. Quantum cryptography is one of the most important branches of such technologies. Different from that of most classical cryptography, the security of quantum cryptography is assured by physical principles such as the Heisenberg uncertainty principle and the quantum no-cloning theorem. Nowadays, quantum cryptography has attracted a great deal of attention since it can achieve unconditional security in theory.The unconditional security of quantum cryptography is, in some sense, based on its special information coding method. This paper mainly studies two kinds of usual information coding methods in quantum cryptography, i.e., quantum state coding and unitary operation coding, and some other interesting ones such as nonselective measurement coding and chronological order coding. We analyze and summarize the characteristics and advantages of the above information coding methods, and then solve some concrete problems in quantum cryptography based on them.On the quantum state coding side, we propose the first secure multiparty quantum key agreement protocol utilizing single photon state and prove its security against both external attacks and participant attacks. Besides, utilizing a special state of a single photon with multiple optical pulses, we design a quantum key distribution (QKD) based quantum private query (QPQ) protocol, which is the first QKD based QPQ with no failure probability and no additional information leak of the database. Finally, we put forward a new eavesdropping detection strategy, utilizing which, the participants can control the generated key in a certain extent. This new strategy for eavesdropping detection broadens the application scope of quantum state coding in quantum cryptography.On the unitary operation coding side, we study two properties of the entanglement swapping and the local unitary operation, based on which, we find out an error in an attack strategy to a quantum secret sharing protocol employing collective eavesdropping detection and furthermore, we improve the above attack strategy. On this basis, we analyze the reason of the insecurity of two three-party QKD protocols. Then we propose a model of multiparty quantum cryptography protocolutilizing single photon and collective eavesdropping detection and prove its security. Finally, based on the above model, we design a quantum private comparison protocol which is more efficient and easier to realize than the previous ones.On the other quantum information coding side, we propose a QKD protocol utilizing an interesting information coding method, i.e., nonselective measurement coding. In this QKD protocol, one of the participants only needs to equip "damaged"measurement devices. Besides, we find that variable timings of the messages in quantum position verification (QPV) protocols might improve the security. More concretely, we present a QPV protocol where the timing of the messages informs the verifier about the basis in which the quantum information has been encoded. And we prove the proposed QPV protocol is secure against adversaries in the bounded-attack-frequency model. This new style of QPV, denoted as different time QPV (DTQPV), has broken the previous no-go theorem for QPV, since DTQPV is secure in the bounded-attack-frequency model even if the adversaries has pre-shared infinite entangled resource.