RIS-Based Physical Layer Security for Integrated Sensing and Communication: A Comprehensive Survey

Integrated sensing and communication (ISAC) is a crucial component of future wireless networks, enabling seamless integration of Communication and Sensing (C&S) functionalities. However, ensuring security in ISAC systems remains a significant challenge, as both C&S data are susceptible to adversarial threats. Physical layer security (PLS) has emerged as a key framework for mitigating these risks at the transmission level. Reconfigurable intelligent surfaces (RIS) further enhance PLS by dynamically shaping the radio environment to improve both secrecy along with C&S performance. This survey begins with an overview of RIS, PLS, and ISAC fundamentals, establishing a foundation for understanding their integration. The state-of-the-art RIS-assisted PLS approaches in ISAC systems are then categorized into passive RIS (PRIS) and active RIS (ARIS) paradigms. PRIS-based techniques focus on optimizing system throughput, covert communication, and secrecy rates (SRs), alongside improving sensing signal-to-noise ratio (SNR) and weighted sum rate (WSR) under various constraints. ARIS-based strategies extend these capabilities by actively optimizing beamforming to enhance secrecy and covert rates while ensuring robust sensing under communication and security constraints. By reviewing both passive and ARIS-based security frameworks, this survey highlights the transformative role of RIS in strengthening ISAC security. Furthermore, it explores key optimization methodologies, technical challenges, and future research directions for integrating RIS with PLS to ensure secure and efficient ISAC in next-generation 6G wireless networks.