Acoustic eavesdropping using a smartphone camera

Abstract

Rolling shutter and movable lens structures widely found in smartphone cameras modulate structure-borne sounds onto camera images, creating a point-of-view optical-acoustic side channel for acoustic eavesdropping. The movement of smartphone camera hardware leaks acoustic information because images unwittingly modulate ambient sound as imperceptible distortions. Experiments have found that the side channel is further amplified by intrinsic behaviors of complementary metal-oxide-semiconductor (CMOS) rolling shutters and movable lenses such as in optical image stabilization (OIS) and auto focus (AF). This disclosure characterizes the limits of acoustic information leakage caused by structure-borne sound that perturbs the point-of-view of smartphone cameras. In contrast with traditional optical-acoustic eavesdropping on vibrating objects, this side channel requires no line of sight and no object within the camera's field of view.