Reconfigurable Intelligent Surface for Physical Layer Key Generation: Constructive or Destructive?

Abstract

Channel Reciprocity-based Key Generation (CRKG) exploits reciprocal channel randomness to establish shared secret keys between wireless terminals. This new security technique is expected to complement existing cryptographic techniques for secret key distribution of future wireless networks. In this paper, we present a new attack, reconfigurable intelligent surface (RIS) jamming, and show that an attacker can prevent legitimate users from agreeing on the same key by deploying a malicious RIS to break channel reciprocity. Specifically, we elaborate on three examples to implement the RIS jamming attack: Using active nonreciprocal circuits, performing time-varying controls, and reducing the signal-to-noise ratio. The attack effect is then studied by formulating the secret key rate with a relationship to the deployment of RIS. To resist such RIS jamming attacks, we propose a countermeasure that exploits wideband signals for multipath separation. The malicious RIS path is distinguished from all separated channel paths, and thus the countermeasure is referred to as contaminated path removal-based CRKG (CRP-CRKG). We present simulation results, showing that legitimate users under RIS jamming are still able to generate secret keys from the remaining paths. We also experimentally demonstrate the RIS jamming attack by using commodity Wi-Fi devices in conjunction with a fabricated RIS prototype. In our experiments, we were able to increase the average bit disagreement ratio (BDR) of raw secret keys by 20%. Further, we successfully demonstrate the proposed CRP-CRKG countermeasure to tackle RIS jamming in wideband systems as long as the source of randomness and the RIS propagation paths are separable.

Information-Theoretic Secure Key Sharing for Wide-Area Mobile Applications

“…Several solutions can be used to facilitate the practical usage of CRKG in slowly varying environments. One solution is to introduce helper devices, e.g., relays and reconfigurable intelligent surface (RIS) to boost the key generation rate and randomness [14]. However, this solution encounters some practical problems, such as the unavailability of trust relays and additional hardware overheads of RIS devices.…”

Joint Transmit and Reflective Beamforming for RIS-assisted Secret Key Generation

“…Consequently, Alice's combined channel gain, ĥa , and Bob's channel gains, ĥb , are highly correlated. After the following procedures of the PKG, i.e., quantization, information reconcilation, and privacy amplification, the channel gains are finally converted into secret keys [7]. Since these steps are similar to those used in existing PKG methods, in this paper, we focus on the channel probing step, where the transmit and reflective beamforming are optimized to maximize the KGR.…”

Secret Key Generation With Multiantenna Relays

“…A relaying SKG scheme was proposed in [8], although this did not consider frequency-selective channels but focussed on a more general approach. An alternative or supplement to relays is reconfigurable intelligent surfaces, which have been considered for SKG [9]. However, they have limited processing abilities and function more as an RF signal reflector which precludes more advanced precoding schemes.…”