When Physical Layer Key Generation Meets RIS: Opportunities, Challenges, and Road Ahead

Physical layer key generation (PLKG) is a promising technology to obtain symmetric keys between a pair of wireless communication users in a plug-and-play manner. The shared entropy source almost entirely comes from the intrinsic randomness of the radio channel, which is highly dependent on the wireless environments. However, in some static/block fading wireless environments, it is hard to guarantee the intrinsic randomness of the wireless channel. Thanks to reconfigurable intelligent surfaces (RISs) with their excellent ability on electromagnetic wave control, the wireless channel environment can now be customized. In this article, we overview the RIS-aided PLKG in static indoor environments, including its channel model and hardware architectures. Then we propose potential application scenarios and analyze the design challenges of RIS-aided PLKG, including channel reciprocity, RIS reconfiguration speed, and RIS deployment via proof-of-concept experiments on a RIS-aided PLKG prototype system. In particular, our experimental results show that the key generation rate is 15-fold higher than that without RIS in a static indoor environment. Next, we design a RIS jamming attack via a prototype experiment and discuss its possible attack-defense countermeasures. Finally, several conclusions and future directions are identified.