RIS-assisted physical layer key generation by exploiting randomness from channel coefficients of reflecting elements and OFDM subcarriers

Abstract

Physical layer key generation is a lightweight technique to establish secret keys securely between resource-constrained devices, but it is ineffective when wireless channels are static or blocked. Physical layer key generation is improved by the use of reconfigurable intelligent surfaces (RISs) to control massive reflecting elements. The channel coefficients of massive reflecting elements serve as a source of randomness for generating secret keys. However, the correlation between the channel coefficients of reflecting elements and OFDM subcarriers causes measurement redundancy, which poses a threat to secret keys. We analyze the secret key rate (SKR) and construct analytical expressions for it. Furthermore, we propose a preprocessing method for decorrelating the measurements, which greatly reduces the computational complexity. Simulation results validate the SKR, bit disagreement ratio (BDR), and randomness. Compared to existing schemes, the proposed scheme greatly improves the SKR.