Study On Design Of Quantum Cryptographic Protocols And Related Issues

Quantum cryptography is the combination of quantum mechanics and classical cryptography. Compared with classical cryptosystems, quantum cryptosystems have two representative advantages. One is the provable security (even unconditional security) and the other is the eavesdropping detectability. Therefore, quantum cryptography has inherent advantage in the sense of security and it has gradually developed into an important branch of modern cryptography. It is implied by the research both in theory and in experiment that quantum cryptography would grow up in the next generation of technologies in cryptography.The contributions of this dissertation mainly involves three areas in quantum cryptographic protocols, including quantum key distribution (QKD), quantum secret sharing (QSS), and protocols related to quantum secure direct communication (QSDC).In the field of QKD, three novel protocols are developed in theory based on different quantum properties. The first protocol is a robust QKD against collective noise based on the notion of decoherence-free subspace. It provides a favorable solution for the problem that quantum states are very fragile and tend to be destroyed by decoherence due to the unwanted coupling with the environment during the QKD process. Compared with the similar schemes, this protocol not only has higher efficiency and stronger security, but also is easy to be implemented. The second one is a QKD based on the technique of the reusable measurement base sequence (MBS). It is designed creatively by using the unsymmetrical mode of MBS, which can eliminate the relativity between the receiver's MBS and his chosen measurement bases. Therefore, the privacy of MBS can be guaranteed. Furthermore, the robustness of this protocol is strengthened. The third QKD protocol, which has a high efficiency, is based on the idea of the intra-particle hybrid entanglement. In this protocol, the information carriers are transmitted by combining the interference phenomenon and the time delay technique.With respect to the field of QSS, three new theoretical protocols are proposed based on quantum technologies such as entanglement swapping and dense coding. In the QSS based on Bell measurement, all agents need do nothing but measure the quantum states in hand with the Bell basis no matter which secret will be shared and how many participants there are. So it is easy to be generalized. The other two QSS protocols realize bidirectional authentication and controllable secret rebuild while carrying out the QSS task, respectively. They are suitable for different application requirements. In addition, the common eavesdropping strategies are combined with the advantages of the participant attack according to the properties of QSS. The frangibility of two existing QSS protocols are analyzed, respectively, under intercept-resent attack and forcible measurement attack taken by participants. Two advisable improvements are presented, respectively, based on their original traits.In our studies on the protocols related to QSDC, a multiparty conversation scheme is designed. This scheme based on multi-level Greenberger-Horne-Zeilinger (GHZ) states and dense coding is analogous to the international group conversation protocol in Client/Server (C/S) mode. It can implement a group secure conversation in the quantum communication network. Moreover, an attack strategy which is effective for the quantum secure telephone protocol is presented. And a reasonable and robust improved version of this protocol is also proposed.