TLDR

We recovered speech from light reflected from various
desktop ornaments, beverage cans, and other objects using
a photodiode from a distance of 25 meters. 

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Abstract

In this paper, we introduce "the little seal bug" attack, an optical side-channel attack which exploits lightweight reflective objects (e.g., an iced coffee can, a smartphone stand, a souvenir) as optical implants for the purpose of recovering the content of a conversation. We 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 are often placed on desks, can provide the infrastructure required for eavesdroppers to recover the content of a victim’s conversation held when the victim is sitting at his/her desk. First, we conduct a series of experiments aimed at learning the characteristics of optical measurements obtained from shiny objects that reflect light, by using a photodiode to analyze the movement of a shiny weight in response to sound. Based on our findings, we propose an optical acoustical transformation (OAT) to recover speech from the optical measurements obtained from light reflected from shiny objects. Finally, we compare the performance of the little seal bug attack to related methods presented in other studies. We 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 at a desk that contains a reflective object.