Arrow: Capture the Inaudible Attacker in 3D Space via Smart-speaker

Recent works have shown that inaudible signals (at ultrasound frequencies) can become audible to the microphone by exploiting the nonlinear effects. With a well-designed inaudible signal, an adversary can control Amazon Echo and Google Homelike devices in people’s rooms silently and remotely. A voice command like “Alexa, open the door“ can be a serious treat. Although recent works design various methods against such inaudible attacks, one important issue remains open: there is no clear solution to locate the attack source accurately. Obviously, the only way to completely eliminate such inaudible threats is to locate and remove the attack source. This paper is an attempt to close this gap. We propose Arrow, an effective method to help users locate the ultrasound attack source in 3D space indoors. Arrow establishes the relationship between inaudible signals and the recorded sounds of the microphone, and then explores the architecture of the embedded microphone array on smart speaker for extracting a 3D direction-specific signature. By learning such directional signature, Arrow can accurately estimate the spatial orientation of the inaudible attack source and help users to locate and remove it. We implement a prototype of Arrow and conduct comprehensive experiments to validate its performance. The results show Arrow can achieve 2.5° and 7° error in DoA(Direction of Arrival) estimation for horizontal and vertical angles, respectively.