With the emergence of the Internet of Things (IoT) technology, wireless connectivity should be more ubiquitous than ever. In fact, the availability of wireless connection everywhere comes with security threats that, unfortunately, cannot be handled by conventional cryptographic solutions alone, especially in heterogeneous and decentralized future wireless networks. In general, physical layer security (PLS) helps in bridging this gap by taking advantage of the fading propagation channel. Moreover, the adoption of reconfigurable intelligent surfaces (RIS) in wireless networks makes the PLS techniques more efficient by involving the channel into the design loop. In this article, we conduct a comprehensive literature review on the RIS-assisted PLS for future wireless communications. We start by introducing the basic concepts of RISs and their different applications in wireless communication networks and the most common PLS performance metrics. Then, we focus on the review and classification of RIS-assisted PLS applications, exhibiting multiple scenarios, system models, objectives, and methodologies. In fact, most of the works in this field formulate an optimization problem to maximize the secrecy rate (SR) or secrecy capacity (SC) at a legitimate user by jointly optimizing the beamformer at the transmitter and the RIS’s coefficients, while the differences are in the adopted methodology to optimally/sub-optimally approach the solution. We finalize this survey by presenting some insightful recommendations and suggesting open problems for future research extensions.

中文翻译：

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通过反射智能表面实现智能和安全的无线通信：简短调查

随着物联网（IoT）技术的出现，无线连接应该比以往任何时候都普遍存在。实际上，无处不在的无线连接都带来了安全威胁，不幸的是，传统的加密解决方案无法单独应对这种安全威胁，尤其是在异构和分散的未来无线网络中。通常，物理层安全性（PLS）通过利用衰落传播信道来帮助弥合这一差距。此外，在无线网络中采用可重配置智能表面（RIS）可通过将信道纳入设计环路来提高PLS技术的效率。在本文中，我们对用于未来无线通信的RIS辅助PLS进行了全面的文献综述。我们首先介绍RIS的基本概念及其在无线通信网络中的不同应用以及最常见的PLS性能指标。然后，我们专注于RIS辅助PLS应用程序的审查和分类，展示了多种方案，系统模型，目标和方法。实际上，该领域的大多数工作都提出了一个优化问题，即通过共同优化发射机处的波束形成器和RIS的系数来最大化合法用户的保密率（SR）或保密容量（SC）。以最佳/次最佳方式采用该解决方案的方法。我们通过提出一些有见地的建议，并为将来的研究扩展提出未解决的问题，来完成本次调查的最终确定。