Challenge-response is a security mechanism well known for authentication using encryption. Recently, we have proposed a new challenge-response mechanism in the context of physical layer security (PLS). The verifier, instead of sending a challenge, changes the physical properties of the electromagnetic environment and expects to receive a properly modified signal from the device under verification. We thus have introduced the concept of partially controllable channels that enable such signal propagation medium changes. Among prominent example of partially controllable channels, the thesis will focus on intelligent reflective surfaces (IRSs).

An IRS is a panel of tiled metamaterial elements that reflect impinging radio signals with controllable phases, steering them in desired directions. A particular choice of the phase values for all IRS elements provides an IRS configuration. In future cellular networks, IRSs are envisioned to be controlled by base stations, mostly with the objective of increasing coverage, especially at high frequencies (both for millimeter waves and in the THz band).

For our authentication purpose, Bob is the base station, which also exclusively controls the IRS, while Alice and Eve are devices in the cell. Bob has a controllable channel available, according to the selected IRS configuration. IRSs are suitable for CR PLS authentication, as they have a high and controllable directivity, thus providing significantly different channels to different devices (Alice and Eve in our scenario).

The thesis will study the use of IRSs for authentication in a 6G system context, developing solution for selection of the configuration to be used for authentication, the steps needed to estimate the channel, and proper functions to be used to decide if the received message is authentic or not, based on the "response" to the challenge.

For more information contact prof. Stefano Tomasin (stefano.tomasin@unipd.it)