In the paper, a protocol of quantum secure direct communication (QSDC) based on EPR entangled state and a quantum state of one particle is presented. The proposed protocol of QSDC uses the idea of one time pad of classical cryptology. The concept of data block and the method of split-step transmission are introduced into the proposed protocol of QSDC. According to the property of quantum, the eavesdropper can get nothing from quantum communication system, so the security of whole QSDC system is ensured. A part of secret message which will be transmitted is loaded on entangled states by processing quantum dense encoding operation on entangled particles. A nonorthogonal mixed state of single particle is introduced into the proposed protocol in order to improve the transmission efficiency, hence another part of secret message which will be transmitted is loaded on states of single particle. The private key and secret message are transmitted directly at the same time on quantum channel. So the proposed scheme of QSDC shall gain higher efficiency as well as complexity increase, and the system be proved the security by performance analysis.
In the paper, a protocol of quantum secure direct communication (QSDC) based on EPR entangled state and a quantum state of one particle is presented. The proposed protocol of QSDC uses the idea of one time pad of classical cryptology. The concept of data block and the method of split-step transmission are introduced into the proposed protocol of QSDC. According to the property of quantum, the eavesdropper can get nothing from quantum communication system, so the security of whole QSDC system is ensured. A part of secret message which will be transmitted is loaded on entangled states by processing quantum dense encoding operation on entangled particles. A nonorthogonal mixed state of single particle is introduced into the proposed protocol in order to improve the transmission efficiency, hence another part of secret message which will be transmitted is loaded on states of single particle. The private key and secret message are transmitted directly at the same time on quantum channel. So the proposed scheme of QSDC shall gain higher efficiency as well as complexity increase, and the system be proved the security by performance analysis.
Quantum secure direct communication (QSDC) is one of the most important branches of quantum communication. In contrast to the quantum key distribution (QKD) which distributes a secure key between distant parties, QSDC directly transmits secret message instead of sharing key in advance. To establish a secure QSDC protocol, on the one hand, the security of the quantum channel should be confirmed before the exchange of the secret message. On the other hand, the quantum state should be transmitted in a quantum data block since the security of QSDC is based on the error rate analysis in the theories on statistics. Compared with the deterministic quantum key distribution (DQKD) which can also be used to transmit deterministic information, QSDC schemes do not need extra classical bits to read the secret message except for public discussion. In this article, we introduce the basic principles of QSDC and review the development in this field by introducing typical QSDC protocols chronologically. The first QSDC protocol was proposed by Long and Liu, which can be used to establish a common key between distant parties. In their scheme, the method for transmitting quantum states in a block by block way and in multiple steps was proposed and the information leakage before eavesdropping detection was solved. Subsequently, Deng et al. presented two pioneering QSDC schemes, an entangled-state-based two-step QSDC scheme and a single-photon-state-based quantum one-time pad scheme, in which the basic principle and criteria for QSDC were pointed out. From then on, many interesting QSDC schemes have been proposed, including the high-dimension QSDC scheme based on quantum superdense coding, multi-step QSDC scheme based on Greenberger-Horne-Zeilinger states, QSDC scheme based on quantum encryption with practical non-maximally entangled quantum channel, and so on. We also introduce the anti-noise QSDC schemes which were designed for coping with the collective-dephasing noise and the collective-rotation noise, respectively. In 2011, Wang et al. presented the first QSDC which exploited the hyperentangled state as the information carrier and several QSDC schemes based on the spatial degree of freedom (DOF) of photon, single-photon multi-DOF state and hyperentanglement were proposed subsequently. In addition to the point-to-point QSDC schemes, we also review the QSDC networks. Finally, a perspective of QSDC research is given in the last section.
By studying the properties of the mixture of Bell state particles and single photons,in the paper we design a quantum code scheme with high coding capacity,and propose a novel quantum secure direct communication protocol with high transmission efficiency.Alice prepares Bell state particles and single photons,and divides Bell state particles into two sequences SA and SB.SB is sent to Bob for the first security check through using quantum correlation properties of particles.When the check result shows that the quantum channel is safe,by using the designed quantum code scheme, Alice encodes her classical message on the mixed quantum state sequence of Bell sequence SA and single photon sequence SS.Then,some single photons that are used for security check are re-inserted randomly into the encoded sequence,and the order of particles is rearranged to ensure checking Eve's attack.Alice sends the new sequence to Bob.Bob delays and receives it.And then,the quantum channel conducts the second-time security check.The transmission error rate is calculated,and if the error rate is lower than the tolerance threshold,the channel is safe.Bob decodes and reads Alice's message.The first security check is to determine whether quantum channel is safe.The second security check is to test whether there are eavesdroppers during information transmission.Safety analysis is done by applying the quantum information theory for the proposed protocol.The error rate introduced by Eve and the amount of information by Eve are calculated.It is shown that this pro-tocol can effectively resist measurement-resend attack,intercept-resend attack, auxiliary particle attack,denial of service attack and Trojan attack.Among them,auxiliary particle attack is analyzed in detail.The transmission efficiency and coding capacity are also analyzed.The transmission efficiency is 2,the quantum bit rate is 1,and the coding capacity is that a quantum state can encode three bits of classical messages.We also compare the proposed protocol with many existing popular protocols in the sense of efficiency,e.g.,Ping-Pong protocol, Deng F G et al.'s two-step and one-pad-time quantum secure direct communication protocol,Wang J et al.'s quantum secure direct communication protocol based on entanglement swapping and Quan D X et al.'s one-way quantum secure direct communication protocol based on single photon.It is proved that this proposed protocol has higher transmission efficiency.In addition,neither complex U operation nor entanglement swapping is used,and implementation process is simplified.However,this protocol is devoted to theoretical research of quantum secure direct communication.There are still some difficulties in the practical application.For example,the storage technology of quantum states is not mature at present.It is not easy to prepare and measure Bell state particles nor to combine them with single photons,and so on.The implementation of this protocol depends on the development of quantum technology in the future.
In order to improve the communication efficiency and security of Quantum Secure Direct Communication, a new Quantum Secure Direct Communication scheme based on d-dimension Bell entangled state is proposed. In the scheme, the receiver and the sender transport the d-dimensional Bell particles as secure test particles to ensure the security of communication. The receiver can calculate the security of the channel according to the measurement of d-dimensional Bell state particles, which is based on the entanglement properties of the d-dimensional Bell state. Secret information is transmitted through the other d-dimensional Bell state particles by dense coding technique. Then, the receiver can determine the security of the channel by comparing the measurements of the particles and makes a joint measurement of the transmitted particles to obtain secret information. Finally, the entropy theory is used to analyze the security of the protocol. Under the four dimensional Bell state, the transmission efficiency of the protocol is 90.90% and the efficiency of the quantum bit is 45.45%. The results show that the proposed scheme is safe and reliable and has high transmission efficiency.
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.
Quantum secure direct communication (QSDC) enables the message sender to directly transmit messages to the message receiver through quantum channel without keys. Environmental noise is the main obstacle for QSDC's practicality. For enhancing QSDC's noise robustness, we introduce the quantum error correction (QEC) code into QSDC and propose the QSDC protocol based on the redundancy code. This QSDC protocol correlates atomic state with the electron–photon entangled pairs and transmits photons in quantum channels for two rounds. The parties can construct the remote atomic logical entanglement channel and decode messages with the heralded photonic Bell state measurement (BSM) and single electron measurement. This QSDC protocol is unconditionally secure in theory and has some advantages. First, benefiting from the heralded photonic BSM, it can eliminate the influence from photon transmission loss and has the potential to realize long-distance secure message transmission. Second, taking use of the error correction function of the repetition code, the error rate caused by the decoherence during the second round of photon transmission can be reduced, which can reduce the message error and increase the secret message capacity. Third, the whole protocol is feasible under current experimental condition. Our QSDC protocol can be extended to use other stronger QEC code. It provides a promising method to promote QSDC's practicality in the future.
Quantum secure direct communication (QSDC) is an important branch of quantum communication that is capable of directly transmitting secret messages over a quantum channel. It may be viewed as a concrete realization of Wyner's wiretap channel theory, which ensures the reliable and secure communication of information in the presence of noise and eavesdropping. Hence it is a fully-fledged quantum-communications protocol, which does not require a separate secret key negotiation phase. By contrast, its quantum key distribution (QKD) counterpart represents a secret key-negotiation protocol, which has to be followed up by a separate classical communication session. The essential difference between these two modes of quantum communication lies in the employment of a block-based data transmission technique, proposed by Long and Liu in 2000. However, the original block-based data transmission requires quantum memory, which is not widely available at the time of writing. Recently, this difficulty has been overcome by using classical coding theory, which has been successfully applied to the single-qubit DL04 QSDC. Here we will present a single-photon-memory QSDC protocol based on entangled pairs of photons. We commence by comparing QSDC to QKD, followed by an example of the single-photon QSDC and single-photon QKD protocol. Then we continue by modifying the so-called two-step QSDC protocol designed for deterministic QKD by reducing the number of qubits in a block into a single one, in which Alice prepares Einstein-Podolsky-Rosen (EPR) photon pairs and partitions them into two parts: the so-called pioneer qubit and the follow-up qubit. The pioneer photon is transferred first to Bob, while the follow-up photon is used either for performing encoding or for eavesdropping detection. Bob extracts the candidate key by combining the two particles of the EPR pair to perform Bell-basis measurement. Then the protocol is transformed into a single-photon-memory QSDC using coding theory. Our theoretical analysis shows that the resultant protocol is robust to individual attacks. Additionally, a high communication efficiency is achieved.