  Reconfigurable intelligent surface (RIS) facilitates the extraction of
unpredictable channel features for physical layer key generation (PKG),
securing communications among legitimate users with symmetric keys. Previous
works have demonstrated that channel reciprocity plays a crucial role in
generating symmetric keys in PKG systems, whereas, in reality, reciprocity is
greatly affected by hardware interference and RIS-based jamming attacks. This
motivates us to propose LoCKey, a novel approach that aims to improve channel
reciprocity by mitigating interferences and attacks with a loop-back
compensation scheme, thus maximizing the secrecy performance of the PKG system.
Specifically, our proposed LoCKey is capable of effectively compensating for
the CSI non-reciprocity by the combination of transmit-back signal value and
error minimization module. Firstly, we introduce the entire flowchart of our
method and provide an in-depth discussion of each step. Following that, we
delve into a theoretical analysis of the performance optimizations when our
LoCKey is applied for CSI reciprocity enhancement. Finally, we conduct
experiments to verify the effectiveness of the proposed LoCKey in improving
channel reciprocity under various interferences for RIS-assisted wireless
communications. The results demonstrate a significant improvement in both the
rate of key generation assisted by the RIS and the consistency of the generated
keys, showing great potential for the practical deployment of our LoCKey in
future wireless systems.
