Steganalysis and improvement of a quantum steganography protocol via GHZ4 state

Quantum steganography that utilizes quantum mechanical effect to achieve the purpose of information hiding is a popular topic of quantum information. Recently, El Allati et al. proposed a new quantum steganography using GHZ₄ state. Since all of the 8 groups of unitary transformations used in the secret message encoding rule change the GHZ₄ state into 6 instead of 8 different quantum states when the global phase is not considered, we point out that a 2-bit instead of a 3-bit secret message can be encoded by one group of the given unitary transformations. To encode a 3-bit secret message by performing a group of unitary transformations on the GHZ₄ state, we give another 8 groups of unitary transformations that can change the GHZ₄ state into 8 different quantum states. Due to the symmetry of the GHZ₄ state, all the possible 16 groups of unitary transformations change the GHZ₄ state into 8 different quantum states, so the improved protocol achieves a high efficiency.     

An Improved Quantum Information Hiding Protocol Based on Entanglement Swapping of χ-type Quantum States

In 2011, Qu et al. proposed a quantum information hiding protocol based on the entanglement swapping of χ-type quantum states. Because a χ-type state can be described by the 4-particle cat states which have good symmetry, the possible output results of the entanglement swapping between a given χ-type state and all of the 16 χ-type states are divided into 8 groups instead of 16 groups of different results when the global phase is not considered. So it is difficult to read out the secret messages since each result occurs twice in each line (column) of the secret messages encoding rule for the original protocol. In fact, a 3-bit instead of a 4-bit secret message can be encoded by performing two unitary transformations on 2 particles of a χ-type quantum state in the original protocol. To overcome this defect, we propose an improved quantum information hiding protocol based on the general term formulas of the entanglement swapping among χ-type states.     

Quantum Steganography via Greenberger-Horne-Zeilinger GHZ_4 State

A quantum steganography communication scheme via Greenberger-Horne-Zeilinger GHZ 4 state is constructed to investigate the possibility of remotely transferred hidden information.Moreover,the multipartite entangled states are become a hectic topic due to its important applications and deep effects on aspects of quantum information.Then,the scheme consists of sharing the correlation of four particle GHZ4 states between the legitimate users.After insuring the security of the quantum channel,they begin to hide the secret information in the cover of message.Comparing the scheme with the previous quantum steganographies,capacity and imperceptibility of hidden message are good.The security of the present scheme against many attacks is also discussed.     

Quantum steganography with a large payload based on dense coding and entanglement swapping of Greenberger-Horne-Zeilinger states

A quantum steganography protocol with a large payload is proposed based on the dense coding and the entanglement swapping of the Greenberger-Horne-Zeilinger (GHZ) states. Its super quantum channel is formed by building up a hidden channel within the original quantum secure direct communication (QSDC) scheme. Based on the original QSDC, secret messages are transmitted by integrating the dense coding and the entanglement swapping of the GHZ states. The capacity of the super quantum channel achieves six bits per round covert communication, much higher than the previous quantum steganography protocols. Its imperceptibility is good, since the information and the secret messages can be regarded to be random or pseudo-random. Moreover, its security is proved to be reliable.     

集体噪声信道上带身份认证的无信息泄露的量子对话协议

在集体噪声条件下提出三个带身份认证的量子对话协议,两个量子对话协议分别用于抵抗集体消相干噪声和集体旋转噪声,另一个用于同时抵抗这两种集体噪声.通信双方通过广义幺正变换将自己的秘密信息编码到量子态中;并根据自己的秘密信息和携带秘密信息的粒子的初末两量子态,便可推知对方的秘密信息实现量子对话.协议的效率、安全性和无信息泄露等性能分析表明了协议的有效性.     

二粒子纠缠态受控传递的最佳量子通道

本文研究了如何在二粒子纠缠态的量子受控传递中选择最佳量子通道的问题。分别利用四粒子GHZ态和四粒子特殊"反关联GHZ态"作为量子通道,本文提出了二粒子反关联纠缠态的量子受控传递的两个方案。通过对比两个方案下接受者最后采取的幺正操作的具体矩阵形式,分析了待传量子纠缠态与量子通道的关系,指出了四粒子GHZ态和四粒子特殊"反关联GHZ态"分别是二粒子正关联和反关联纠缠态各自隐形传递应该选择的最佳的量子通道。     

利用纠缠GHZ态实现受控的量子确定性安全通讯(英文)

提出一个受控的量子确定性安全通信方案,在通信过程中,纠缠GHZ态用作量子信道,秘密信息的编码和破解是通过受控的量子纠缠交换和局域酉变换实现的.此方案是安全的.关于此方案安全性的证明和两步方案[Phys.Rev.A 68 042317]的安全性是一样的.此方案也可以推广到有多方控制者参与的情形.     

Two schemes of multiparty quantum direct secret sharing via a six-particle GHZ state

In this paper, two new efficient multiparty quantum direct secret sharing schemes are proposed via a six-particle GHZ state and Bell measurements. In the first scheme, based on the theory of security cryptanalysis, the secret message of the sender is directly encoded into the transmitted particles, and all the agents can obtain their information by performing bell measurement on the received particles, and then cooperate to recover the information of the sender. In the second scheme, we define a new secret shared coding method by performing local unitary operations on the transmitted particles, then agents perform Bell measurements on their own particles respectively, and feedback the measurement to the dealer. If the agent's results are matched with the previous coding method, the protocol will work out.In addition, the proposed two schemes have the following common advantages: the sender can send all prepared particles to the receiver, and can send an arbitrary key to the receiver, rather than a random secret key; the proposed schemes do not need to insert any detection sets to detect eavesdropping and can resist both existing attacks and spoofing attacks by dishonest agents. The sender need not to retain any photons, so the sender's quantum memory could be omitted here.     

Controlled Teleportation of an Unknown N-qubit Entangled GHZ State

A scheme for controlled teleportation of an unknown N-qubit entangled GHZ state from the sender Alice to the distant receiver Bob is proposed. And m-qubit GHZ state is sufficient for the task of control by m spatially- separated supervisors. Conditioned on the local operations executed by all participants, Bob can faithfully restore the original state by performing relevant unitary transformations with the aid of some classical message about measurement results. Anyone＇s absence will absolutely lead to the failure of teleportation.     

Scheme for sharing classical information via tripartite entangled states

We investigate schemes for quantum secret sharing and quantum dense coding via tripartite entangled states. We present a scheme for sharing classical information via entanglement swapping using two tripartite entangled GHZ states. In order to throw light upon the security affairs of the quantum dense coding protocol, we also suggest a secure quantum dense coding scheme via W state by analogy with the theory of sharing information among involved users.     

Quantum Secure Direct Communication Using Six-Particle Maximally Entangled States and Teleportation

The sender shares six-particle maximally entangled states as quantum channel with the receiver. If the quantum channel is secure, the sender performs projective measurements and tells the measurement outcome to the receiver. The receiver performs the unitary transformations and makes projective measurements on his particles to obtain the secret information. Using teleportation, the transmission of three-qubit secret information can be completed in each quantum channel     

A Novel Quantum Covert Channel Protocol Based on Any Quantum Secure Direct Communication Scheme

By analyzing the basic properties of unitary transformations used in a quantum secure direct communication (QSDC) protocol, we show the main idea why a covert channel can be established within any QSDC channel which employs unitary transformations to encode information. On the basis of the fact that the unitary transformations used in a QSDC protocol are secret and independent, a novel quantum covert channel protocol is proposed to transfer secret messages with unconditional security. The performance, including the imperceptibility, capacity and security of the proposed protocol are analyzed in detail.     

Several teleportation schemes of an arbitrary unknown multi-particle state via different quantum channels

We first provide four new schemes for two-party quantum teleportation of an arbitrary unknown multi-particle state by using three-, four-, and five-particle states as the quantum channel, respectively. The successful probability and fidelity of the four schemes reach 1. In the first two schemes, the receiver can only apply one of the unitary transformations to reconstruct the original state, making it easier for these two schemes to be directly realized. In the third and fourth schemes, the sender can preform Bell-state measurements instead of multipartite entanglement measurements of the existing similar schemes, which makes real experiments more suitable. It is found that the last three schemes may become tripartite controlled teleportation schemes of teleporting an arbitrary multi-particle state after a simple modification. Finally, we present a new scheme for three-party sharing an arbitrary unknown multi-particle state. In this scheme, the sender first shares three three-particle GHZ states with two agents. After setting up the secure quantum channel, an arbitrary unknown multi-particle state can be perfectly teleported if the sender performs three Bell-state measurements, and either of two receivers operates an appropriate unitary transformation to obtain the original state with the help of other receiver's three single-particle measurements. The successful probability and fidelity of this scheme also reach 1. It is demonstrated that this scheme can be generalized easily to the case of sharing an arbitrary unknown multi-particle state among several agents.     

Quantum secret sharing between m-party and n-party with six states

A quantum secret sharing scheme between an m-party group and an n-party group is proposed using three conjugate bases.A sequence of single photons,each of which is prepared in one of the six states,is used directly to encode classical information in the quantum secret sharing process.In this scheme,each of all m members in group 1 chooses randomly his/her own secret key individually and independently,and directly encodes his/her respective secret information on the states of single photons via unitary opera...     

Quantum Dialogue by Using Non-Symmetric Quantum Channel

A protocol for quantum dialogue is proposed to exchange directly the communicator＇s secret messages by using a three-dimensional Bell state and a two-dimensional Bell state as quantum channel with quantum superdence coding, local collective unitary operations, and entanglement swapping. In this protocol, during the process of trans- mission of particles, the transmitted particles do not carry any secret messages and are transmitted only one time. The protocol has higher source capacity than protocols using symmetric two-dimensional states. The security is ensured by the unitary operations randomly performed on all checking groups before the particle sequence is transmitted and the application of entanglement swapping.     

Multiparty Quantum Remote Secret Conference

We present two schemes for multiparty quantum remote secret conference in which each legitimate conferee can read out securely the secret message announced by another, but a vicious eavesdropper can get nothing about it. The first one is based on the same key shared efficiently and securely by all the parties with Greenberger-Horne- Zeilinger （GHZ） states, and each conferee sends his secret message to the others with one-time pad crypto-system. The other one is based on quantum encryption with a quantum key~ a sequence of GHZ states shared among all the conferees and used repeatedly after confirming their security. Both these schemes are optimal as their intrinsic efficiency for qubits approaches the maximal value.     

Probabilistic Teleportation of a Three-Particle GHZ State via Two Three-Particle Entangled W States

A scheme for teleporting an unknown three-particle GHZ state from a sender to either one of two receivers is proposed. In this scheme, the quantum channel is composed of two non-maximally three-particle entangled W states. An unknown three-particle GHZ state can be perfectly teleported probabilistically if the sender performs two generalized Bell-state measurements and the Hadamard operation while either one of two receivers introduces an ancillary particle which is one of the final three particle constituting the teleported state, then performs the controlled-not operation with the ancillary particle as the target bit and introduces an appropriate unitary transformation with the help of the other receiver's simple measurements. All kinds of unitary transformations are given in detail. The present scheme may be directly generalized to teleport an unknown multiparticle GHZ state via two three-particle entangled W states used as the quantum channel.     

Large payload quantum steganography based on cavity quantum electrodynamics

A large payload quantum steganography protocol based on cavity quantum electrodynamics (QED) is presented in this paper, which effectively uses the evolutionary law of atoms in cavity QED. The protocol builds up a hidden channel to transmit secret messages using entanglement swapping between one GHZ state and one Bell state in cavity QED together with the Hadamard operation. The quantum steganography protocol is insensitive to cavity decay and the thermal field. The capacity, imperceptibility and security against eavesdropping are analyzed in detail in the protocol. It turns out that the protocol not only has good imperceptibility but also possesses good security against eavesdropping. In addition, its capacity for a hidden channel achieves five bits, larger than most of the previous quantum steganography protocols.     

基于GHZ纠缠态实现纯EPR对的双向量子隐形传态

提出了一种基于Greenberger-Horne-Zeilinger(GHZ)纠缠态进行纯EPR对双向隐形传态的方案.通过使用纠缠交换技术,通信双方Alice和Bob共享两对三粒子GHZ纠缠态来构建量子信道.方案中通过使用受控非门操作,单量子位测量以及适当的幺正操作,通信双方可以同时发送一个纯EPR对给对方.故相比仅可以传送单一量子态的方案更经济.     

Multi-state Quantum Teleportation via One Entanglement State

A multi-sender-controlled quantum teleportation scheme is proposed to teleport several secret quantum states from different senders to a distance receiver based on only one Einstein-Podolsky-Rosen (EPR) pair with controlled-NOT (CNOT) gates. In the present scheme, several secret single-qubit quantum states are encoded into a multi-qubit entangled quantum state. Two communication modes, i.e., the detecting mode and the message mode, are employed so that the eavesdropping can be detected easily and the teleported message may be recovered efficiently. It has an advantage over teleporting several different quantum states for one scheme run with more efficiency than the previous quantum teleportation schemes.