From One Form of Energy to Another

Abstract

Wireless sensing has gained significant research interest in recent years. However, the focus has primarily been on improving sensing performance, such as enhancing accuracy, and little attention has been paid to the security aspects of wireless sensing. In this paper, we demonstrate that acoustic signal-based sensing, widely regarded as the safest wireless sensing modality due to its physical characteristics, can be stealthily attacked and compromised. The core of this stealthy injection attack lies in exploiting the “photoacoustic effect” to convert the energy of laser light into vibrations, inducing acoustic signals, which are then used to compromise acoustic sensing systems. It is important to note that the laser can be invisible to the human eye, and the acoustic signals it generates are inaudible to human ears. To make the attack even stealthier, we propose the concept of “Smartphone-Defined Laser” to use commodity smartphones to control low-cost laser hardware ($0.60), eliminating the need for bulky and expensive signal generators. Through hardware and software co-design, we successfully demonstrate the attack with smartphones and cheap laser hardware. Comprehensive experiments show that the proposed attack can compromise the state-of-the-art acoustic sensing techniques (both chirp-based and continuous wave-based), achieving a high average success rate of 96.1% across different tasks even when the target is 50 m away. We hope our findings raise awareness of the security risks associated with acoustic sensing and encourage further research into enhancing its security.