AI summaryⓘ
The authors study how to verify a user's identity based on the unique features of their signal's path using a special surface that controls signal reflections (RIS). They consider a scenario where the legitimate user has one antenna, but an attacker has multiple antennas and tries to fake the identity using advanced signal techniques. The authors find the attacker's best way to trick the system and when Bob, the verifier, cannot tell if the signal is from the real user or the attacker. Their analysis shows that if the signal paths are complex, the attacker cannot easily impersonate the user, but if the path is simple and direct, impersonation is possible. They confirm these findings with simulations and examine the system's overall security.
Physical layer authenticationReconfigurable Intelligent Surface (RIS)PrecodingChannel estimationMultiple antennasLine-of-sight (LOS)Signal propagationChannel indistinguishability
Authors
Linda Senigagliesi, Anna V. Guglielmi, Marco Baldi, Stefano Tomasin
Abstract
In physical layer authentication, verification of a user's identity is based on the characteristics of the transmission channel through which signals are delivered to the authenticator (Bob). In this paper, we assume that the signals received by Bob pass through a \ac{RIS} (controlled by Bob) and that the legitimate transmitter (Alice) is equipped with one antenna. Conversely, the attacker (Trudy) has multiple antennas and uses precoding to deceive Bob's verification. Assuming that Trudy knows all the channel matrices, we first derive her optimal attack strategy. Then, we analyse the conditions under which the channel estimated by Bob is indistinguishable when either Alice or Trudy is transmitting. When Trudy has a single antenna, we show that the indistinguishability condition cannot be met when the channels to the RIS are the result of propagation over multiple paths. For single-path line-of-sight (LOS) conditions, instead, Trudy can impersonate Alice although transmitting from a different position. We verify these results numerically and assess the security of the considered scenario, even when the indistinguishability conditions cannot be met.