Design And Analysis On Multi-party Quantum State Sharing Protocols

With the rapid development of quantum information technology,classical cryptosystems whose security is based on computational complexity assumptions is severely challenged. In order to deal with this problem, people begin to investigate quantum cryptography. Quantum cryptography is the combination of quantum mechanics and classical cryptography. The security of quantum cryptosystems is 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 important merit in security, quantum cryptography has been attracted extensive attention and become one of the significant research branches of cryptography. The early research on quantum cryptography was mainly concentrated on the two-party protocols. With the progress of the research,the design and analysis on multi-party quantum cryptography protocol is becoming a hot topic.In this dissertation the basic theory, the design and analysis of multi?party (including three-party) quantum state sharing (QSTS) protocols have been discussed. On the one hand, according to the symmetrical characteristic of quantum resource that it might be held by all the intermediate agents, symmetrical and asymmetrical QSTS protocols have been researched. On the other hand, according to the quantum information whether all of the initial information can be recovered accurately,deterministic and probabilistic QSTS protocols have been considered.Then, the security of multi-party QSTS protocols have been analyzed from the views of outside and participant attacks in detail. Finally, the qubit efficiency, total efficiency, complexity of measurement and operations of the proposed QSTS protocols have been analyzed. Compared with some another QSTS protocols, two improved QSTS ones have been put forward.The main contributions and innovations of this dissertation are summarized as follows.Firstly, through researching and studying two kinds of famous quantum secret communication protocol (B393 quantum teleportation and HBB99 quantum secret sharing) mechanisms, a deterministic multi-party QSTS protocol has been designed and it can be realized by using the four-particle x-style entangled state as quantum information carrier. The four-particle x-style entangled state can be prepared easily in a physical system.In this QSTS protocol, all of initial shared quantum information can be recovered accurately with a 100% successful probability. It is shown that the proposed multi-party QSTS protocol has some good performances of quantum and classical resource consumptions, complexity of measurement and operations. Moreover, in this dissertation the security of the deterministic multi-party protocol has been analyzed based on decoy photons detection technology, invisible photons tracing detection technology, correlation elicitation technology and entropic uncertainty principle, respectively.Secondly, through researching more QSTS protocols, it is shown that in many QSTS protocol the initial shared quantum state cannot be recovered accurately with a 100% successful probability due to the shared quantum states, but only reach a certain successful probability. In this dissertation another four-particle entangled state - AKLT ground state have been found and realized easily in a physical system. And then a probabilistic four-party QSTS protocol has been designed. Owing to the special structure of AKLT ground state, the initial quantum state information can be obtained and recovered accurately with a 50%successful probability. Then, the security of the probabilistic QSTS protocol has been analyzed by means of the safety factor function and robustness of AKLT ground state. Moreover, compared with some other probabilistic QSTS protocols, some advantanges and disadvantangs of the proposed protocol have been presented from the views of qubit efficiency,total efficiency, complexity of measurement and operations, respectively.Finally, the main differences of symmetrical and asymmetrical QSTS protocols have been researched according to the symmetrical characteristic of quantum resource that it might be hold by all the intermediate agents. It has been showed that symmetrical QSTS protocols usually exist some redundancy particles, thus those protocols may consume some unnecessary quantum and classical resources and increase the complexity of measurement and operations. Then the symmetrical ZZZM protocol has been analyzed based on GHZ-like entangled states and an improved asymmetrical QSTS one has been proposed. Though the ZZZM protocol has many excellent characteristics such as high efficiency, simple feasibility and universality, it exists some redundant quantum resources.And the improved protocol can reduce some unnecessary quantum and classical resource consumptions, meanwhile the total efficiency has also reached the upper bound of theoretical value. Moreover, according to the negative partial transpose measure and von Neumann entropy measure,some entanglement characteristics of multi-qubit Brown states have been discussed in detail. The MP protocol has been extended, and then two-party quantum teleportation and multi-party QSTS protocols of an arbitrary unknown single and two-qubit state have also been discussed by using the generalized seven-qubit Brown state. In addition, an asymmetrical QSTS for an arbitrary unknown three-qubit state has been presented based on the NLLS protocol. It can be viewed as the improved one of NLLS protocol.And then the improved protocol can be toleranted of some noise effects and reduced some classical resource consumptions.