Quantum Direct Communication Protocol Research Articles

Quantum direct communication protocol using recurrence in k -cycle quantum walks

The ability of quantum walks to evolve in a superposition of distinct quantum states has been used as a resource in quantum communication protocols. Under certain settings, the $k$-cycle discrete-time quantum walks\,(DTQW) are known to recur to its initial state after every $t_r$ steps. We first present a scheme to optically realize any $k$-cycle DTQW using $J$-plate, orbital angular momentum\,(OAM) sorters, optical switch, and optical delay line. This entangles the polarization and OAM degrees of freedom\,(DoF) of a single photon. Making use of this recurrence phenomena of $k$-cycle DTQW and the entanglement generated during the evolution, we present a new quantum direct communication protocol. The recurrence and entanglement in $k$-cycle walk are effectively used to retrieve and secure the information, respectively, in the proposed protocol. We investigate the security of the protocol against intercept and resend attack. We also quantify the effect of amplitude damping and depolarizing noises on recurrence and mutual information between polarization and OAM DoF of a single photon.

Quantum direct communication protocols using discrete-time quantum walk

The unique features of quantum walk, such as the possibility of the walker to be in superposition ofthe position space and get entangled with the position space, provides inherent advantages that canbe captured to design highly secure quantum communication protocols. Here we propose two quan-tum direct communication protocols, a Quantum Secure Direct Communication (QSDC) protocoland a Controlled Quantum Dialogue (CQD) protocol using discrete-time quantum walk on a cycle.The proposed protocols are unconditionally secure against various attacks such as the intercept-resend attack, the denial of service attack, and the man-in-the-middle attack. Additionally, theproposed CQD protocol is shown to be unconditionally secure against an untrusted service providerand both the protocols are shown more secure against the intercept resend attack as compared tothe qubit based LM05/DL04 protocol.

Controller-independent quantum bidirectional communication using non-maximally entangled states

In the recent past, Mohapatra and Balakrishnan (Quantum Inf Process 16:147, 2017) proposed a controller-independent bidirectional quantum direct communication protocol using Bell states. In this work, we show the possibility of the achieving same protocol with non-maximally entangled states without compromising on the security and the efficiency of the protocol. We exploit the degree of entanglement as an additional security parameter. By doing so, the eavesdropper always gets detected in the initial stages of the protocol in the case of an intercept and resend attack. On the other hand, there is only 25% chance that the eavesdropper goes undetected in the initial stages of the protocol proposed by Mohapatra and Balakrishnan. Thus, the proposed protocol can be implemented with the viable physical resources.

Quantum signature for designated verifier with strong security

Most of the classical designated verifier signature schemes are insecure against quantum adversary. In this paper, a quantum signature scheme for the designated verifier is proposed. In our scheme, during the initialization phase, the partners share secret keys by performing the quantum key distribution protocol. On the other hand, by performing the quantum direct communication protocol, the key generator center shares secret keys with the signer and the designated verifier, respectively. The key generator center generates a particle sequence of Bell state and distributes the particles between the signer and the designated verifier. During the signature generation phase, the signer encrypts the particle sequence by the secret keys and Hardmard operators. After that, the signer performs the controlled unitary operations on the encrypted particle sequence so as to generate the quantum signature. The designated verifier can simulate the quantum signature by performing the same symmetric signing steps as that performed by the original signer. Hence, the quantum signature signed by the true signer is the same as the one simulated by the receiver, which makes our scheme possess the designated properties. During the signature verification phase, the designated verifier performs the controlled unitary operations on the quantum signature and obtains the quantum ciphertexts. After that, the designated verifier decrypts the quantum ciphertexts by the symmetric secret keys and Hardmard operators so that the quantum signature can be verified. Our signature is secure against forgery attack, inter-resending attacks and Trojan horse attack. Because the trace distance between the density operators of different quantum signatures is zero, the information-theoretical security of our quantum signature scheme can be proved. The unconditionally secure quantum key distribution protocol and the one-time pad encryption algorithm can guarantee the security of the secret keys shared by the partners. What is more, the security assumption about the key generation center is weak. That is, it is not necessary to assume that the key generation center should be fully trusted. On the other hand, in our scheme, the quantum one-way function is not used. To generate a quantum signature, the signer need not prepare for entangled particle sequence. To verify a quantum signature, the verifier need not apply any state comparison to the received particles. The qubit efficiency is 100%. Therefore, our scheme has the advantages in the security and efficiency over the other quantum signature schemes for the designated verifier.

Controller-Independent Bidirectional Direct Communication with Four-Qubit Cluster States

We propose a feasible scheme for implementing bidirectional quantum direct communication protocol using four-qubit cluster states. In this scheme, the quantum channel between the sender Alice and the receiver Bob consists of an ordered sequence of cluster states which are prepared by Alice. After ensuring the security of quantum channel, according to the secret messages, the sender will perform the unitary operation and the receiver can obtain different secret messages in a deterministic way.

Controller-independent bidirectional quantum direct communication

Recently, Chang et al (Quantum Inf Process,14,3515,2015) proposed a controlled bidirectional quantum direct communication protocol using Bell states. In this work, the significance of Bell states, which are being used as initial states in Chang et al. protocol, is elucidated. The possibility of preparing initial state based on the secret message of the communicants is explored. In doing so,the controller-independent bidirectional quantum direct communication protocol has evolved naturally. It is shown that any communicant cannot read the secret message without knowing the initial states generated by the other communicant. Further,intercept and resend attack and information leakage can be avoided. The proposed protocol is like a conversion between two persons without the help of any third person with high-level security.

“Counterfactual” quantum protocols

The counterfactuality of recently proposed protocols is analyzed. A definition of “counterfactuality” is offered and it is argued that an interaction-free measurement (IFM) of the presence of an opaque object can be named “counterfactual”, while proposed “counterfactual” measurements of the absence of such objects are not counterfactual. The quantum key distribution protocols which rely only on measurements of the presence of the object are counterfactual, but quantum direct communication protocols are not. Therefore, the name “counterfactual” is not appropriate for recent “counterfactual” protocols which transfer quantum states by quantum direct communication.

Quantum direct communication protocol strengthening against Pavičić’s attack

A quantum circuit providing an undetectable eavesdropping of information in message mode, which compromises all two-state [Formula: see text]-[Formula: see text] quantum direct communication (QDC) protocols, has been recently proposed by Pavičić [Phys. Rev. A 87 (2013) 042326]. A modification of the protocol’s control mode is proposed, which improves users’ 25% detection probability of Eve to 50% at best, as that in ping-pong protocol. The modification also improves the detection probability of Wójcik’s attack [Phys. Rev. Lett 90 (2003) 157901] to 75% at best. The resistance against man-in-the-middle (MITM) attack as well as the discussion of security for four Bell state protocols is presented. As a result, the protocol security is strengthened both theoretically and practically, and quantum advantage of superdense coding is restored.

The Security Analysis of Two-Step Quantum Direct Communication Protocol in Collective-Rotation Noise Channel**Supported by the National Natural Science Foundation of China under Grant Nos 61472048, 61402058, 61272511, 61472046, 61202082 and 61370194, the Beijing Natural Science Foundation under Grant No 4152038, and the China Postdoctoral Science Foundation Funded Project under Grant No 2014M561826.

To analyze the security of two-step quantum direct communication protocol (QDCP) by using Einstein–Podolsky–Rosen pair proposed by Deng et al. [Phys. Rev. A 68 (2003) 042317] in collective-rotation noise channel, an excellent model of noise analysis is proposed. In the security analysis, the method of the entropy theory is introduced, and is compared with QDCP, an error rate point Q0(M : (Q0, 1.0)) is given. In different noise levels, if Eve wants to obtain the same amount of information, the error rate Q is distinguishable. The larger the noise level ϵ is, the larger the error rate Q is. When the noise level ϵ is lower than 11%, the high error rate is 0.153 without eavesdropping. Lastly, the security of the proposed protocol is discussed. It turns out that the quantum channel will be safe when Q < 0.153. Similarly, if error rate Q > 0.153 = Q0, eavesdropping information I > 1, which means that there exist eavesdroppers in the quantum channel, and the quantum channel will not be safe anymore.

Intercept-and-resend attack on controlled bidirectional quantum direct communication and its improvement

Recently, Ye and Jiang (Chin Phys Lett 30(4):040305, 2013) proposed two controlled bidirectional quantum direct communication protocols by using a Green---Horne---Zeilinger state and a Bell state. This paper shows that a malicious user, Bob, can obtain the other user's secret message without the controller's permission by performing an intercept-and-resend attack. An improvement is then proposed to avoid this problem.

Two Quantum Direct Communication Protocols Based on Quantum Search Algorithm

Based on the properties of two-qubit Grover’s quantum search algorithm, we propose two quantum direct communication protocols, including a deterministic secure quantum communication and a quantum secure direct communication protocol. Secret messages can be directly sent from the sender to the receiver by using two-qubit unitary operations and the single photon measurement with one of the proposed protocols. Theoretical analysis shows that the security of the proposed protocols can be highly ensured.

On the propagation of quantum correlations in a cavity quantum electrodynamics network

In this paper we present the analysis of a quantum direct communication protocol. Based on the propagation of quantum correlations, we analyze a model of two chains of atoms inside cavities, joined by optical fibers, which can be used as a quantum communication protocol. We study the dynamics of the entanglement and the quantum discord, using the generalized master equation. We first study the free evolution of the quantum correlations through the cavity network and compare it with the case where an eavesdropper has performed a measurement on one of the cavities. We also find the quantum discord to be a more robust measure of the quantum correlations and study the optimal initial condition to detect the eavesdropper.

Measure-and-Resend Attack and Improvement on “A Scheme to Share Information via Employing Discrete Algorithm to Quantum States”

In 2011, Kang and Fang (Commun. Theor. Phys. 55:239–243, 2011) presented a quantum direct communication protocol using single photons. This study points out a pitfall in Kang and Fang’s scheme, in which an eavesdropper can launch a measure-and-resend attack on this scheme to reveal the secret message. Furthermore, an improved scheme is proposed to avoid the attack.

Fault tolerant authenticated quantum direct communication immune to collective noises

This study proposes two new coding functions for GHZ states and GHZ-like states, respectively. Based on these coding functions, two fault tolerant authenticated quantum direct communication (AQDC) protocols are proposed. Each of which is robust under one kind of collective noises: collective-dephasing noise and collective-rotation noise, respectively. Moreover, the proposed AQDC protocols enable a sender to send a secure as well as authenticated message to a receiver within only one step quantum transmission without using the classical channels.

Comment on “Improvement of Controlled Bidirectional Quantum Direct Communication Using a GHZ State" [Chin. Phys. Lett. 30 (2013) 040305

The problem of definite information leakage existing in the controlled bidirectional quantum direct communication protocol using GHZ states [Chin. Phys. Lett. 23 (2006) 1680] was pointed out by Ye and Jiang [Chin. Phys. Lett. 30 (2013) 040305]. Then, they proposed two strategies to improve this security bug. However, if the revised versions are analyzed from the viewpoint of information theory, it can be found that they still have the problem of information leakage. That is, three quarters and one half of the information interchanged by the communication parties are leaked out unknowingly in the first and second revised protocols, respectively.

In quantum direct communication an undetectable eavesdropper can always tellΨfromΦBell states in the message mode

We show that in any quantum direct communication protocol that is based on $\ensuremath{\Psi}$ and $\ensuremath{\Phi}$ Bell states, an eavesdropper can always tell $\ensuremath{\Psi}$ from $\ensuremath{\Phi}$ states without altering the transmission in any way in the message mode. This renders all protocols that make use of only one $\ensuremath{\Psi}$ state and one $\ensuremath{\Phi}$ state completely insecure in the message mode. All four-Bell-state protocols require a revision and this might be of importance for new implementations of entanglement-based cryptographic protocols. The detection rate of an eavesdropper is 25$%$ per control transmission, i.e., a half of the rate in the two-state (ping-pong) protocol. An eavesdropper can detect control probes with certainty in the standard control transmission without a photon in the Alice-to-Bob's travel mode and with near certainty in a transmission with a fake photon in the travel mode. Resending of measured control photons via the travel mode would make an eavesdropper completely invisible.

Improved eavesdropping detection strategy based on four-particle cluster state in quantum direct communication protocol

In order to improve the eavesdropping detection efficiency in a two-step quantum direct communication protocol, an improved eavesdropping detection strategy using the four-particle cluster state is proposed, in which the four-particle cluster state is used to detect eavesdroppers. During the security analysis, the method of the entropy theory is introduced, and two detection strategies are compared quantitatively using the constraint between the information that the eavesdropper can obtain and the interference that has been introduced. If the eavesdroppers intend to obtain all information, the eavesdropping detection rate of the original two-step quantum direct communication protocol using EPR pair block as detection particles will be 50%; while the proposed strategy’s detection rate will be 75%. In the end, the security of the proposed protocol is discussed. The analysis results show that the eavesdropping detection strategy presented is more secure.

Quantum Authenticated Direct Communication Using Bell States

Two protocols of quantum direct communication with authentication [Phys. Rev. A 73:042305, 2006] were recently proposed by Lee, Lim and Yang, based on the correlation of Greenberger-Horne-Zeilinger (GHZ) states. However, Zhang et al. showed that in the two protocols the authenticator Trent can eavesdrop the secret message by subtle strategies [Phys. Rev. A 75:026301, 2007]. In this paper, we propose two authenticated quantum direct communication (AQDC) protocols using Bell states. Users can identify each other by checking the correlation of Bell states. Alice can directly send a secret message to Bob without any previously shared secret using the remaining Bell states after authentication. The two proposed AQDC protocols are implemented under the condition that there is a quantum link between Alice and Bob and that there is no quantum link between Alice and Bob respectively, similar to the ones proposed by Lee, Lim and Yang [Phys. Rev. A 73:042305, 2006]. The proposed AQDC protocols not only fix the leaks in the AQDC protocols proposed by Lee, Lim and Yang, but also economize the quantum resource.

Improved Eavesdropping Detection Strategy in Quantum Direct Communication Protocol Based on Five-Particle Cluster State

In order to improve the eavesdropping detection efficiency in two-step quantum direct communication protocol, an improved eavesdropping detection strategy using four-particle GHZ state is proposed, in which four-particle GHZ state is used to detect eavesdroppers. During the security analysis, the method of the entropy theory is introduced, and two detection strategies are compared quantitatively by using the constraint between the information which eavesdropper can obtain and the interference introduced. If the eavesdroppers intend to obtain all information, the eavesdropping detection rate of the original two-step quantum direct communication protocol by using EPR pair block as detection particles is 50%; while the proposed strategy's detection rate is 88%. In the end, the security of the proposed protocol is discussed. The analysis results show that the eavesdropping detection strategy presented is more secure.

Improved quantum “Ping-pong” protocol based on GHZ state and classical XOR operation

In order to transmit the secure message, a deterministic secure quantum direct communication protocol which was called “Ping-pong” protocol was proposed by Bostrom and Felbinger [Bostrom K, et al. Phys Rev Lett, 2002, 89: 187902]. But the protocol was proved very vulnerable, and can be attacked by an eavesdropper. An improved “Ping-pong” protocol is presented to overcome the problem. The GHZ state particles are used to detect eavesdroppers, and the classical XOR operation which serves as a one-time-pad is used to ensure the security of the protocol. During the security analysis, the method of the entropy theory is introduced, and three detection strategies are compared quantitatively by using the constraint between the information which an eavesdropper can obtain and the interference introduced. If the eavesdropper gets the full information, the detection rate of the original “Ping-pong” protocol is 50%; the detection rate of the second protocol which used two particles of EPR pair as detection particles is also 50%; and the detection rate of the presented protocol is 75%. In the end, the security of the proposed protocol is discussed. The analysis results show that the improved “Ping-pong” protocol in this paper is more secure than the other two.