Reconfigurable-Intelligent-Surface-Assisted Secret Key Generation Under Spatially Correlated Channels in Quasi-Static Environments

Abstract

Physical layer key generation (PLKG) can significantly enhance the security of classic encryption schemes by enabling them to change their secret keys significantly faster and more efficiently. However, due to the reliance of PLKG techniques on channel medium, reaching a high key generation rate (KGR) is challenging in quasi-static environments. Recently, exploiting reconfigurable intelligent surface (RIS) as a means to induce randomness in quasi-static wireless channels has received significant research interest. However, the impact of spatial correlation between the RIS elements is rarely studied. To be specific, for the first time, in this contribution, we take into account a spatially correlated RIS which intends to enhance the KGR in a quasi-static medium. Closed-form analytical expressions for KGR are derived for the two cases of random phase shift (RPS) and equal phase shift (EPS) in the RIS elements. We also analyze the temporal correlation between the channel samples to ensure the randomness of the generated secret key sequence. It is shown that the EPS scheme can effectively exploit the inherent spatial correlation between the RIS elements and it leads to a higher KGR compared to the widely used RPS strategy. We further formulate an optimization problem in which we determine the optimal portion of time dedicated to direct and indirect channel estimation within a coherence time. We show the accuracy and the fast convergence of our proposed sequential convex programming (SCP) based algorithm and discuss the various parameters affecting spatially correlated RIS-assisted PLKG.

A Powerful Adversary Model and Corresponding Time OTP Slot Allocation Scheme in RIS-Assisted Physical Layer Key Generation

“…This is difficult to achieve in a quasi-static environment [9,10]. To solve the problem, reconfigurable intelligent surface (RIS) is usually used to improve the key rate [11][12][13][14]. RIS is able to change the amplitude and phase of the reflected signals to reconfigure the radio environment [15].…”