Research On Quantum Multiparty Secure Communication

As information technology develops rapidly in recent years, information security is becoming increasingly important. The emergence of quantum infor-mation has a profound impact on information security. While quantum algo-rithms seriously threaten the safety of the widely used public-key cryptosystem, quantum cryptography opens up a new direction for information security. As a frontier of information science, quantum secure communication has achieved great success in the past few decades and related research has important theoret-ical and practical values. By the virtues of quantum mechanics, quantum secure communication can implement secure and efficient transmission of information. Traditionally, related researches are concentrating on two-party, end-to-end situ-ation. With the progress of research, quantum multiparty secure communication that contains multiple participants has attracted more and more attention.In this dissertation, we focus on the research of quantum multiparty se-cure communication and our research includes the following subjects:quan-tum communication network, quantum multiparty communication protocols and quantum multiparty cryptography. On the one hand, the researches of quantum communication network and quantum multiparty communication protocols are committed to achieving secure transmissions of quantum information. On the other hand, the research of quantum multiparty cryptography focuses on imple-mentations of specific security tasks. The contributions of this dissertation are summarized as follows.1. We study secure distributions of entanglement in quantum network en-vironment firstly. For large scale quantum information processing and quantum computation, it is necessary to consider the network environment. Quantum entanglement plays an essential role in the field of quantum infor- mation and quantum computation. In quantum network, a general assump-tion for many quantum tasks is that the quantum entanglement has been prior shared among participants. Actually, the distribution of entanglement becomes complex in the network environment. We present a theoretical quantum network model with good scalability. Then, three efficient and perfect schemes for the entanglement channel construction are proposed. Some general results for d-level system are also given. In our model, any two communication sites can construct an entanglement channel of Bell states with the assistance of the intermediate sites on their quantum chain. By using the established entanglement channel, n sites can efficiently and perfectly construct an entanglement channel of an n-qudit Greenberger-Horne-Zeilinger (GHZ) state. More importantly, an entanglement channel of an arbitrary n-qudit state can also be constructed among any n sites, or even among any t sites where1≤t≤n. The constructed multiparticle entanglement channels have many useful applications in quantum network environment.2. Based on the securely shared entanglement among participants, we study quantum multiparty communication protocols. In the field of quantum communication, remote state preparation is a specific type of application that could accomplish indirect transmission of a quantum state while pre-venting the quantum state from being tampered. By using the cluster states as the shared quantum resource, we propose several multiparty remote state preparation (MRSP) schemes, including the joint RSP (JRSP) and the controlled RSP (CRSP). The prepared states can be not only a one-qubit state and a two-qubit state, but also a three-qubit state with complex coefficients which has rarely been considered. We also study determinis-tic JRSP schemes to achieve100%success probability. Two new versions of deterministic JRSP schemes of arbitrary one-and two-qubit states are proposed by using the four-and six-qubit cluster states as the shared quan-tum resource, respectively. Compared with previous schemes, our schemes have high efficiency since less quantum resources are required, some addi-tional unitary operations and measurements are unnecessary. Our research points out that the existing two types of deterministic JRSP schemes based on GHZ states and EPR pairs are equivalent. Several general and specific measurement bases are designed to complete the tasks. Moreover, efficient quantum circuits to implement each scheme are given. As the quantum resource, cluster states show good feasibility to implement MRSP. Some particularities of these MRSP schemes are also discussed.3. In the aspect of quantum multiparty cryptography, we deal primarily with quantum secret sharing (QSS) and quantum signature protocols. As an im-portant area of quantum cryptograph, QSS is still a very active research topic in recent years. We study QSS schemes for general access struc-tures rather than the threshold scheme. Using multiparticle entanglements in high-dimensional system, three novel multipartite QSS formalisms for general access structures are proposed. The method for building general access structures in these formalisms is discussed. The major feature of these formalisms is that a variety of secret sharing schemes with differ-ent access structures can be implemented depending on the dealer’s will. Beside, hierarchic and threshold authorized structures can also be built. All of which makes our formalisms highly flexible. Besides, we analyze the security of a high-dimensional deterministic multiparty quantum secret sharing scheme and our research shows that the scheme is vulnerable to a specific kind of collusion attack. In the worst case,n/2+1agents can col-lude elaborately to reveal the dealer’s secret without the help of the other agents. We present the attack strategy in details and also give two possible improvements to resist the proposed collision attack.4. With the development of quantum cryptograph, quantum signature has been introduced to provide unconditionally secure digital signature. In the last part of the dissertation, we focus on the design and cryptanalysis of quantum signature protocols. On the one hand, although some blind quan-tum signature (BQS) protocols have been proposed recently, the previous schemes have security and efficiency problems. Based on the entangled GHZ states, we propose a new weak BQS protocol. Compared with some existing schemes, our protocol has100%efficiency. Besides, the protocol is simple and easy to implement. The security of the protocol is guaran-teed by the correlation of the GHZ particles held by each participant. In our protocol, the signatory is kept blind from the content of the message. According to the security analysis, the signatory cannot disavowal his/her signature while the signature cannot be forged by others. On the other hand, we study the security problems of some BQS schemes. Our research shows that some of the BQS protocols are unable to complete the blind signature task fairly if the verifier is dishonest. Indeed, these protocols can be viewed as variants of classical digital signature scheme of symmetric-key cryptography. If nobody is trusted in such protocols, digital signature cannot be implemented since disagreements cannot be solved fairly.