Quantum-secure communication and computation have garnered increasing attention due to their powerful search capabilities for certain complex problems and their ability to provide unconditional security. This indicates that classical cryptography, such as asymmetric ciphers based on complex mathematics, faces a significant threat from quantum algorithms. However, quantum cryptography can detect any attempt to eavesdrop on a channel. As a result, the investigation and implementation of quantum computers and quantum-secure communication networks have become essential objectives for numerous research teams. This paper provides an overview of quantum cryptography, including its development, and focuses on the theoretical aspect of quantum secure direct communication (QSDC). This helps readers understand the theoretical operating principles and gain a better understanding of the entire quantum characteristic and protocol operation in the QSDC field. QSDC enables secure communication without previously shared private keys, making it a crucial topic in quantum cryptography research. This paper provides an overview of several well-known versions of QSDC in theory, discussing their applications, challenges and potential future directions.

量子安全通信和计算因其对某些复杂问题的强大搜索能力以及提供无条件安全性的能力而受到越来越多的关注。这表明经典密码学，例如基于复杂数学的非对称密码，面临着来自量子算法的重大威胁。然而，量子密码学可以检测任何窃听通道的尝试。因此，量子计算机和量子安全通信网络的研究和实施已成为众多研究团队的重要目标。本文概述了量子密码学，包括其发展，并重点讨论了量子安全直接通信（QSDC）的理论方面。这有助于读者理解理论运行原理，更好地理解QSDC领域的整个量子特性和协议运行。QSDC 无需事先共享私钥即可实现安全通信，这使其成为量子密码学研究中的一个重要课题。本文从理论上概述了 QSDC 的几个著名版本，讨论了它们的应用、挑战和潜在的未来方向。