A Multi-Eavesdropper Scheme Against RIS Secured LoS-Dominated Channel

Reconfigurable intelligent surface (RIS) has been shown as a promising technique to increase the channel randomness for secret key generation (SKG) in low-entropy channels (e.g., static or line-of-sight (LoS)), without small-scale fading. In this letter, we show that even with aid of RIS, collaborative eavesdroppers (Eves) can still estimate legitimate Alice-Bob and erode their rates (SKRs), since RIS induced is also reflected Eves’ observations. Conditioned on observations, if entropy RIS-combined zero, Eves are able it its key. Leveraging this, design multi-Eve scheme against RIS-secured LoS dominated scenarios, by using multiple observations reconstruct channel. We further deduce closed-form leakage rate under our designed scheme, demonstrate results via simulations.