The Little Seal Bug: Optical Sound Recovery from Lightweight Reflective Objects
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Presented at BlackHat Asia 2022 by
In this talk we will introduce "the little seal bug" attack, an optical side-channel attack used to recover sound from lightweight reflective objects; such objects are commonly seen in home offices, which became a primary work setting during the COVID-19 pandemic. We will show how fluctuations in the air pressure on the surface of a shiny object can be exploited by eavesdroppers to recover speech passively and externally, using equipment not likely to be associated with spying. These air pressure fluctuations, which occur in response to sound, cause the shiny object to vibrate and reflect light which modulates the nearby sound; as a result, seemingly innocuous objects like an empty beverage can, desk ornament, or smartphone stand, which is usually placed on desktops, can provide the needed infrastructure required for eavesdroppers to recover the content of a victim's conversation which is held when the victim is sitting/working in front of a desk. First, we conducted a series of experiments aimed at learning the characteristics of optical measurements obtained from a shiny object that reflects light by analyzing the movement of a shiny weight in response to sound using a photodiode. Based on our findings, we proposed an algorithm to recover speech from optical measurements that were obtained from light reflectedfrom shiny objects. Finally, we will compare the performance of the little seal bug attack to related methods presented in other studies. We will show that eavesdroppers located 35 meters away from a victim can use the little seal bug attack to recover speech at the sound level of a virtual meeting with fair intelligibility when the victim is sitting/working at a desk that contains a reflective object.