RIS-Aided Physical Layer Key Generation of IoT Network in Static Environments (March 2023)

Physical layer secret key generation (SKG) technology can provide lightweight encryption for resource-constrained Internet of Things (IoT) devices. However, many IoT devices are stationary, and the environment is usually static, which leads to ultralow/zero secret key rates. To circumvent this problem, a novel SKG scheme based on reconfigurable intelligent surface (RIS) is proposed for multiple-input single-output (MISO) communications. First, the phase shifts at the RIS are tuned randomly in each frame, which makes time-varying reflection channels superimposed on the original channels. Correspondingly, the key capacity of all nodes within the cell coverage area can be remarkably improved. Compared with the existing methods, the scheme is loosely coupled with the original system. Besides, the closed-form expressions of key capacity taking into account eavesdropping are derived for the case studies of independent and correlated channels. Based on these derivations, we can conclude that sharing the same phase shifts randomness will not lead to key information leakage. More importantly, compared with user-introduced randomness schemes, the proposed scheme can maintain good performance even the number of eavesdropping nodes increases. Furthermore, the impacts of critical parameters on key performance are analyzed, respectively, which offers guidelines for system design. Finally, simulation results verify the theoretical analysis.