Design And Analysis Of Multiparty Quantum Cryptographic Protocols

With the rapid development of the quantum information, especially the research of quantum computation, the widely applied classical cryptosystems, whose security is based on computational complexity assumptions, is severely challenged. To settle this problem, people begin to investigate quantum cryptography. Quantum cryptography is the combination of classical cryptography and quantum mechanics. The security of quantum cryptosystems is only guaranteed by the characteristics of quantum mechanics, such as Heisenberg uncertainty principle, non-cloning theorem for an unknown state and the reliably non-distinguishing attribute of non-orthogonal quantum states. Therefore, it is independent of the computational ability of the attackers. By virtue of its significant advantage in security, quantum cryptography has attracted extensive attention from the public and become one of the important research branches of cryptography. The early study on quantum cryptography was mainly concentrated on the protocols which involve two participants. With the progress of the research, the design and analysis of multiparty quantum cryptographic protocols is becoming a research focus of this realm.The contributions of this dissertation are mainly on the related issues of the multiparty quantum cryptographic protocols, including the design of multiparty quantum secure communication protocols, the design of quantum secure multiparty computation protocols, and the analysis and improvement of the related multiparty quantum cryptographic protocols. The details are as follows.In the design of multiparty quantum secure communication protocols:Firstly, we solve the problem of how to construct the unitary operations which are needed in the multiparty quantum cryptographic which employ collective (eavesdropping) detection strategy. And the unitary operations, which can be used to combat with the errors over different collective-noise channels, are given. By utilizing the given unitary operations and the corresponding quantum information carriers, the protocols, which employ collective detection, can be immune to collective noise. Thirdly, a multi-user quantum key distribution protocol is proposed with single particles and collective detection on a star network. By employing this protocol, any two users of the network can accomplish quantum key distribution with the help of a serving center. Compared with the existing quantum multiparty secure communication protocols which also employ collective detection strategy, all the participants (including the serving center) involved in this protocol do not need to have the ability of storing quantum states. That is to say, this protocol is more feasible with the current technology.In the design of quantum secure multiparty computation protocols: Firstly, a kind of efficient multiparty quantum secret sharing protocol and a quantum private comparison of equality protocol are proposed with collective detection, respectively. Compared with the previous relevant protocols, these two protocols have certain advantages in qubit efficiency, realizability or fault-tolerant performance. Secondly, we investigate the issue of how quantum mechanics can be of use in maintaining the anonymity of the participants in multiparty ranking and present three quantum anonymous multiparty, multidata ranking protocols. In each of these protocols, a participant can securely get the correct rankings of his data and nobody else can match the identity to his data.In the analysis and improvement of multiparty quantum cryptographic protocols:Firstly, a multi-user quantum communication network protocol, which utilizes χ-type entangled states, is analyzed. We demonstrate that this protocol is vulnerable to the correlation-elicitation attack from eavesdropper and improve it to be secure against the corresponding attack. Secondly, we analyze the security of a controlled quantum secure direct communication protocol which can be used for online shopping and find that it is vulnerable to the intercept-resend attack from internal betrayer. Accordingly, an improvement of this protocol, which could resist the betrayer’s attack, is proposed. Thirdly, we analyze an efficient multiparty quantum key agreement protocol, which employs single particles and unitary operations, and point out that it can achieve neither privacy nor fairness under the attacks from dishonest participants. Moreover, we briefly discuss the factors that should be considered when designing a really fair and secure quantum key agreement protocol.