Vibrational Covert Channels using Low-Frequency Acoustic Signals
Nikolay Matyunin, Yujue Wang, Stefan Katzenbeisser · 2019
In this paper, we examine how acoustic signals in sub-bass and infrasonic range can be used to establish a vibrational covert channel between speaker-equipped computers and mobile devices. We show that typical consumer speakers are capable of producing low-frequency sounds, which are not perceivable by humans. At the same time, we show that producing such sounds by the speaker's woofer inevitably generates slight vibrations of the speaker and the surface where it is located. Being unnoticeable to people, such vibrations can be captured by the accelerometer sensor of a mobile device located on the same surface. Therefore, information can be encoded into low-frequency sounds played by a speaker and received on a mobile device by analyzing the produced vibrations. Note that access to the accelerometer on modern mobile devices does not require any user permissions, making the transmission completely unnoticeable. We evaluate the presented covert channel for different speakers, apply it to several application scenarios, and give an overview of possible countermeasures.