Wireless eavesdropping on phone conversations has become a major security and safety concern, especially with advancements toward 5G and beyond featuring higher frequencies and higher sensing resolution.
As demonstrated recently, the eavesdropper can direct a millimeter-wave radar system towards the victim, Alice, who is talking on her phone, to detect few-micron-scale vibration patterns. With these tiny displacements being strongly correlated with the generated sound waves, the eavesdropper recovers audio conversation, intercepting sensitive information, all without the victim ever noticing.
Unfortunately, this analog micro-information cannot be encrypted or protected by existing methods, as the eavesdropper deliberately exploits the physical propagation of sound to steal information during interactions between users and the analog world. As such, the acoustic signal is the weakest link in the communication chain of a phone call, making it very challenging to protect with existing methods.