  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.
