A systematic survey on physical layer security oriented to reconfigurable intelligent surface empowered 6G

The 6G system is envisioned to support various new applications with diverse requirements in terms of quality and security. To fulfill diverse and stringent requirements, reconfigurable intelligent surfaces (RIS) have been extensively studied as a 6G enabling technology. RIS can be used to secure communications and boost the system performance, but it leads to new security threats as well. Due to the open nature of the wireless channel, smart radio environment, dynamic network topology, and adversarial machine learning (ML), 6G will face various unprecedented security threats. Given stringent requirements on quality of service (QoS), security, and massive low-cost Internet of Thing (IoT) devices, physical layer security (PLS) by exploiting the random nature of the wireless channel and/or intrinsic hardware imperfection emerges as a complementary approach to secure wireless communications. Meanwhile, the rapid development of artificial intelligence (AI) promotes the development of intelligent PLS solutions and smart attacks. In this paper, we make a comprehensive overview of PLS for RIS-based 6G systems from both defensive and offensive perspectives. We first introduce the vision of the RIS-enabled 6G smart radio environment. Then, typical security risks and requirements on RIS-based 6G are analyzed. After that, the state-of-the-art techniques on PLS are presented. Subsequently, major academic works on the physical layer security solution oriented to RIS are systematically reviewed. Moreover, the latest studies on attacks based on adversarial RIS are discussed in depth. Finally, we identify multiple open issues and research opportunities to inspire further studies for more intelligent PLS to secure the RIS-enabled 6G system.