Teleportation attack on the QSDC protocol with a random basis and order

The quantum secure direct communication （QSDC） protocol with a random basis and order is analysed and an effective attack, i.e. teleportation attack, is presented. An eavesdropper can obtain half of the transmitted secret bits with the help of this special attack. It is shown that quantum teleportation can be employed to weaken the role of the order-rearrangement encryption at least in a certain circumstance. Meanwhile, a possible improvement on this protocol is proposed, which makes it secure against this kind of attack.     

Forcible-Measurement Attack on Quantum Secure Direct Communication Protocol with Cluster State

The security of the quantum secure direct communication （QSDC） protocol with cluster state is analysed. It is shown that the secret would be partially leaked out when an eavesdropper performs forcible measurements on the transmitted particles. With the help of the result in minimum error discrimination, an upper bound （i.e. 40%） of this leakage is obtained. Moreover, the particular measurements which makes the leakage reach this bound are given.     

Cryptanalysis of Multiparty Quantum Secret Sharing of Quantum State Using Entangled States

Security of a quantum secret sharing of quantum state protocol proposed by Guo et al. [Chin. Phys. Lett. 25 （2008） 16] is reexamined. It is shown that an eavesdropper can obtain some of the transmitted secret information by monitoring the classical channel or the entire secret by intercepting the quantum states, and moreover, the eavesdropper can even maliciously replace the secret message with an arbitrary message without being detected. Finally, the deep reasons why an eavesdropper can attack this protocol are discussed and the modified protocol is presented to amend the security loopholes.     

多方控制的量子安全直接通信协议的分析及改进

对一种多方控制的量子安全直接通信协议(WCZT协议)进行了安全性分析,并利用隐形传态给出了一种新的攻击方法.利用该攻击方法,接收方可以在没有征得任何控制方同意的情况下获得发送方的消息,因此该协议是不安全的.对该协议进行了改进,分析表明改进后的协议能够抵抗这种攻击,可以满足多方控制的量子安全直接通信的目的. 关键词： 隐形传态 单光子 多方控制 量子安全直接通信     

三粒子纠缠W态隐形传态的正交完备基展开与算符变换

先是对利用单个两粒子及单个三粒子纠缠态作为量子信道实现三粒子纠缠W态的隐形传态方案进行讨论.然后由波函数的叠加原理与算符变换出发,将体系的总量子量按照Bell基展开实现量子隐形传态,给出了变换算符与实际操作算符之间的联系.进一步验证出变换算符可逆是成功实现三粒子纠缠W态隐形传态的必要条件的结论. 关键词： 三粒子纠缠W态 Bell基展开 变换算符 隐形传态     

Probabilistic teleportation of a non-symmetric three-particle state

This paper proposes a scheme for teleporting a kind of essential three-particle non-symmetric entangled state, which is much more valuable than a GHZ and W state for some applications in quantum information processing. In comparison with previous proposal of teleportation, the resources of entangled states as quantum channel and the number of classical messages required by our scheme can be cut down. Moreover, it is shown that there exists a class of transformations which ensure the success of this scheme, because the two-particle transformation performed by the receiver in the course of teleportation may be a generic two-particle operation instead of a control-NOT (CNOT) operation. In addition, all kinds of transformations performed by sender and receiver are given in detail.     

An efficient quantum secure direct communication scheme with authentication

In this paper an efficient quantum secure direct communication (QSDC) scheme with authentication is presented, which is based on quantum entanglement and polarized single photons. The present protocol uses Einstein--Podolsky--Rosen (EPR) pairs and polarized single photons in batches. A particle of the EPR pairs is retained in the sender's station, and the other is transmitted forth and back between the sender and the receiver, similar to the `ping--pong' QSDC protocol. According to the shared information beforehand, these two kinds of quantum states are mixed and then transmitted via a quantum channel. The EPR pairs are used to transmit secret messages and the polarized single photons used for authentication and eavesdropping check. Consequently, because of the dual contributions of the polarized single photons, no classical information is needed. The intrinsic efficiency and total efficiency are both 1 in this scheme as almost all of the instances are useful and each EPR pair can be used to carry two bits of information.     

基于纠缠交换的多方多级量子密钥分配协议

提出了一种基于纠缠交换的多方多级量子密钥分配协议.构造了一种两方三级系统的完备正交归一化基，利用该正交归一化基和纠缠交换可以实现两方量子密钥分配.同时，三级可以推广到多级以及两方推广到多方，即可以实现基于纠缠交换的多方多级量子密钥分配.这样，利用纠缠交换和多级密钥分配可以极大地提高检测窃听的效率、密钥生成率以及信息容量. 关键词： 量子密钥分配 纠缠交换 多方 多级     

Probabilistic teleportation of multi-particle partially entangled state

Utilizing the generalized measurement described by positive operator-wlued measure, this paper comes up with a protocol for teleportation of an unknown multi-particle entangled （GHZ） state with a certain probability. The feature of the present protocol is to weaken requirement for the quantum channel initially shared by sender and receiver. All unitary transformations performed by receiver are summarized into a formula. On the other hand, this paper explicitly constructs the efficient quantum circuits for implementing the proposed teleportation by means of universal quantum logic operations in quantum computation.     

Robust Multiparty Quantum Secret Sharing against Participant Forcible Manipulation

The security of the multiparty quantum secret sharing protocol proposed by Gao [G. Gao, Commun. Theor. Phys. 52 （2009） 421] is analyzed. It is shown that this protocol is vulnerable since the agents＇ imperfect encryption scheme can be attacked by a powerful participant. We introduce a attack strategy called participant forcible manipulation and analyze the information leakage in this protocol under this attack. At last, we give an improved version of the original protocol. The improved protocol is robust and has the same efficiency as the original one.