Study On The Theory Of Quantum Cryptography Protocol

Quantum information theory is a new subject which combines quantum mechanics and classical information theory. Quantum information theory can exceed the classical limit of information theory in many ways and realize many unimaginable tasks for classical information theory. Quantum information theory provides with new principles and methods for future revolution of information theory. Quantum cryptography utilizes quantum effects to protect the information, which is based on quantum mechanics and classical cryptography. Quantum cryptography is the most possible applicable technology in quantum information theory. Because quantum cryptography provides with unconditional security and the ability of detecting eavesdropping, it has the very important strategic significance and tremendous prospect in applications. Quantum cryptography will exert important effects in information security.Based on the National Natural Science Foundation of China under Grant and the Research Project of National University of Defense Technology, we study the theory of quantum cryptography protocol focusing on the frontier research subjects of quantum cryptography. In the dissertation, we proposed some new quantum cryptography protocols and analyzed the protocols from the aspects of security and efficiency. The object of our dissertation includes two aspects, one is to improve the efficiency of quantum cryptography protocol without losing the security, especially advance the ability of defeating the noise, the other aims to put forward some new quantum protocols for some special cryptographic tasks. The dissertation involves five areas in quantum cryptography protocol, including quantum key distribution, quantum secret sharing, quantum secure direct communication, quantum authentication and quantum broadcast communication.In the field of quantum key distribution and quantum secret sharing, we proposed a controlled quantum key distribution protocol based on multi-particle entanglement, in which the communication parties can only establish a shared key under the permission of the controller. Moreover, the proposed protocol is secure in noise quantum channel. Based on quantum teleportation and multi-particle entanglement, we put forward a quantum secret sharing protocol of secure direct communication. Different from the quantum secret sharing protocol whose object is essentially to allow a sender to establish a random key with the receivers, the significant characteristic of quantum secret sharing of secure direct communication is that the sender can transmit the secret message to the receivers directly. We designed a multiparty quantum secret sharing protocol using Einstein-Podolsky-Rosen pairs and entanglement swapping. Compared with the proposed quantum secret sharing protocol using entanglement swapping, it is unnecessary for the protocol to perform local unitary operation. The efficiency for the protocol is improved.The major achievements on quantum secure direct communication are as follows: We proposed a quantum secure direct communication protocol using the secret order rearrangement of single photon sequence. The security of the protocol is ensured by the secret order of the single photon sequence. The protocol is efficient and applicable. Based on the order rearrangement of single photon sequence, we developed a multiparty controlled quantum secure direct communication protocol which can be applied to some special scenario. The protocol is practicable because it is unnecessary to use entanglement. We designed a quantum secure direct communication protocol using Einstein-Podolsky-Rosen pairs and teleportation. It is unnecessary for the present protocol to ensure the security of the quantum channel before transmitting the secret message. We presented a quantum secure direct communication protocol based on Einstein-Podolsky-Rosen pairs and entanglement swapping. Different from the proposed quantum secure direct communication protocols, the sender can encode his or her secret message on the Einstein-Podolsky-Rosen pairs without ensuring the security of the quantum channel firstly. We designed a quantum secure communication protocol using three-qubit W state. W state is the 3-qubit state in which each pair of qubits has the same and maximum amount of bipartite entanglement. This feature makes the entanglement of W state maximally symmetrically robust against loss of any single qubit. We put forward a quantum secure direct communication protocol with pure entangled state, in which the sender can send the secret message to the receiver directly without maximally entangled states. We presented a multiparty controlled quantum secret direct communication protocol by using Greenberger-Horne-Zeilinger state, in which the sender transmits her three bits of secret message to the receiver directly and the secret message can only be recovered by the receiver under the permission of all the controllers.We presented a multiparty simultaneous quantum identity authentication protocol based on entanglement swapping. The trusted third party can authenticate many users simultaneously. If there are many users waiting for being authenticated by the system, the efficiency for identity authentication can be improved greatly. We showed that the security of the schemes proposed by Lee et al. does not rely on the usage of entanglement and the Greenberger-Horne-Zeilinger triplet states used in their schemes can be replaced by classical correlated states. We put forward an efficient quantum signature protocol of classical messages based on single photon.We proposed three quantum broadcast communication protocols based on entanglement swapping, dense coding and quantum encryption, respectively, which we call them ES-QBC protocol, DC-QBC protocol and QE-QBC protocol. In ES-QBC protocol, a group of users share a group key and Greenberger-Horne-Zeilinger states with the central party. The communication parties utilize randomσ_z basis andσ_x basis measurement to authenticate the users and check the eavesdropping in the transmission line. After authenticating the users, the central party broadcasts his secret message to them by using entanglement swapping. In DC-QBC protocol, based on dense coding, the central party broadcasts the secret to multi-receiver, each of which shares an authentication key and Greenberger-Horne-Zeilinger states with him. In the QE-QBC protocol, the central party also shares an authentication key and Greenberger-Horne-Zeilinger states with each user. The central party first authenticates the users and checks the eavesdropping and then encrypts his secret message by performing controlled-not operation on the secret qubit and the particle in Greenberger-Horne-Zeilinger state. Thus based on quantum encryption, the central party can broadcast the secret to any subset of the legal receivers.