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from the your-android-needs-to-be-more-paranoid dept.
The Register has a story on a new technique which turns commodity devices with microphones and speakers into active sonar systems
The technique, called CovertBand, looks beyond the obvious possibility of using a microphone-equipped device for eavesdropping. It explores how devices with audio inputs and outputs can be turned into echo-location devices capable of calculating the positions and activities of people in a room.
In a paper [PDF] titled "CovertBand: Activity Information Leakage using Music," Rajalakshmi Nandakumar, Alex Takakuwa, Tadayoshi Kohno, and Shyamnath Gollakota describe a way to transmit acoustic pulses in the 18‑20 kHz range, masked by music, from the speaker and tracking sound reflected by the human body using microphones
The project home page includes further details, and the paper details proof of concept implementations on an Android and Smart TV device, which demonstrate both accurate tracking, and the ability to infer information about what the target is doing.
(Score: 2) by MrGuy on Tuesday August 22 2017, @06:15PM
I'm not sure a white noise generator will help with this problem. It might even make it worse.
The idea (as I understand it) is to use sound (coming from a static location) and a microphone (also in a static location) to "map" physical details of the space, and potentially detect when they change. A white noise generator that doesn't move is just another source of sound that can be used for the mapping. Unless you want to use enough power to effectively overload the detector, which I guess could work. But the article also notes that sounds in this band, while themselves inaudible, can be detected by the way they interact with higher harmonics of otherwise audible sound. They talk about which kinds of music you can "hide" the signal in, which implies that having a noise generator going full time could affect the sounds you can actually hear.
A better idea (to my mind, anyways), would be to use a technology similar to what's used in active noise cancelling headphones. Noise cancelling headphones have a microphone to detect sound, and very quickly create a "counter" wave of sound from a speaker in the headphones that's carefully timed to arrive simultaneously with the noise, thus cancelling it out audibly. Active noise cancelling depends on precise timing, which means there's a slight and very precise delay between the microphone hearing the noise, and the speaker creating the counter noise - otherwise they'd arrive off-phase and you'd have WORSE noise. To use that for a jammer, you'd want a combination microphone and speaker that used a variable (and constantly changing) delay factor to repeat the source signal back out. This would create false "echoes" that would make the mapping inaccurate. And if, over time, the delay changes slightly, then the distortion introduced will not be easy to control for over time.