Quantum secure direct communication (QSDC) can transmit secret messages without keys, making it an important branch of quantum communication. We present a hybrid entanglement-based quantum secure direct communication (HE-QSDC) protocol with simple linear optical elements, combining the benefits of both continuous variables (CV) and discrete variables (DV) encoding. We analyze the security and find that the QSDC protocol has a positive security capacity when the bit error rate is less than 0.073. Compared with previous DV QSDC protocols, our protocol has higher communication efficiency due to performing nearly deterministic Bell-state measurement. On the other hand, compared with CV QSDC protocol, this protocol has higher fidelity with large α. Based on these advantages, our protocol may provide an alternative approach to realize secure communication.
Quantum secure direct communication (QSDC) can transmit secret messages without keys, making it an important branch of quantum communication. We present a hybrid entanglement-based quantum secure direct communication (HE-QSDC) protocol with simple linear optical elements, combining the benefits of both continuous variables (CV) and discrete variables (DV) encoding. We analyze the security and find that the QSDC protocol has a positive security capacity when the bit error rate is less than 0.073. Compared with previous DV QSDC protocols, our protocol has higher communication efficiency due to performing nearly deterministic Bell-state measurement. On the other hand, compared with CV QSDC protocol, this protocol has higher fidelity with large α. Based on these advantages, our protocol may provide an alternative approach to realize secure communication.
Quantum secure direct communication (QSDC) is a recently developed practical solution, which transmits secret messages between legitimate parties, without setting up a cryptographic key. The QSDC protocols are mainly classified into entanglement-based and single photon-based approaches. Their security has been analyzed using Wyner's wiretap channel theory, and their secrecy capacity has been calculated [1]. Hitherto, QSDC protocols have been implemented on optical fiber and free-space channels, all in discrete-variable (DV) encoding that employs single-photon detectors [1]–[2]. However, the implementation of continuous-variable (CV) QSDC, in which the keys are encoded into the quadratures of quantized electromagnetic fields (e.g., coherent states) and detected via homodyne techniques, is preferred due to: its lower costs, excellent integrability with existing optical communication systems, easy implementation from state preparation to measurement, and fast experimental realization. Furthermore, it has been proved that CV-QSDC protocols using squeezed states show higher tolerance in purely lossy channels and enhanced robustness against highly noisy ones, as well [3]. Nevertheless, none of the CV-QSDC protocols employing either coherent or squeezed quantum states have been implemented yet.
Abstract Quantum secure direct communication (QSDC) enables the direct transmission of secret messages over a quantum channel without prior key sharing. QSDC implemented in the continuous-variable (CV) regime allows high-capacity information transmission using simple optical communication technologies. In this work, we propose a novel CV-QSDC protocol with a quantum one-time pad, which achieves secure message transmission based on coherent states and unitary operations, and the receiver can directly obtain the secret messages after measuring the coherent states. The security of this protocol is jointly guaranteed by one-time pad encryption and a CV quantum key distribution (QKD) protocol. Performance analysis shows that the proposed scheme can achieve a quantum bit error rate (QBER) lower than 1% by adjusting the modulation variance and unitary operation parameters. With the optimal modulation variance, the secure transmission distance of the proposed protocol can exceed 150 km.
Quantum secure direct communication (QSDC) realizes the transmission of secret messages directly in a quantum channel. A continuous-variable- (CV) based quantum-communication system allows high-speed, large-capacity information transmission in optical telecommunication systems. In this work, we propose a QSDC protocol based on Gaussian mapping. As for Gaussian modulation, the designed Gaussian-mapping scheme effectively solves the problem, which results from the nonuniformity of the secret-message bitstream, and is applicable to different modulation variances. The system performance analysis shows that the proposed scheme can realize inerrant Gaussian modulation of secret messages, and secure transmission of messages under information theory. Moreover, our work hopes to stimulate discussion on experimental realization and practical advance of CV-QSDC protocol.
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.
As one of the most important branches of quantum cryptography, quantum secure direct communication (QSDC) is used to transmit the secret message directly rather than distribute a random key. Quantum homomorphic encryption (QHE) enables arbitrary quantum transformation on encrypted data without decrypting the data. To date, the previously proposed QSDC schemes are mainly based on different quantum states. The research of the QSDC scheme based on QHE is still blank. In this paper, a QSDC scheme by taking advantage of the properties of QHE is proposed. The proposed protocol has applied QHE and decoy photons to prevent various types of attacks. The proposed scheme only utilizes the rotation operation to encode the secret message which is easy to implement with the current technologies. Moreover, the communication efficiency and the qubit-utilization ratio are analyzed in this paper, which shows that this protocol has good performance in the qubit-utilization ratio, and the qubit efficiency of the QSDC scheme has improved.
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.