Defensive-RIS against Eavesdropping and False Data Injection relying on Non-Reciprocal Links

Reconfigurable Intelligent Surfaces (RISs) have excellent beam steering capabilities, which is applied to enhance wireless communication systems as a customizable signal reflector. Recently, these surfaces are used to disrupt the existing communication systems by introducing new types of vulnerability to the physical layer, commonly known as RIS-In-The-Middle (RITM) attack. An adversary uses RIS to replace the direct channel between two transceivers, and hence it can eavesdrop on all exchanged data by the legitimate users, but also perform a false data injection to the receiver. This work proposes anti-attack techniques based on a non-reciprocal channel produced by a defensive-RIS (D-RIS). The proposed precoding and combining methods and the channel estimation procedure for a nonreciprocal link are robust against potential adversaries while keeping the existing advantages of the RIS. We analyse the robustness of the system against attacks in terms of achievable secrecy rate and probability of detecting fake data. We believe that this defensive role of RIS can be a basis for new protocols and algorithms in the area.