The most paranoid of which we already know the checklist to avoid modern audio eavesdropping: Clean your home or office for bugs. Put your phone in a Faraday bag — or refrigerator. Consider even stripping the internal microphone from your devices. Now, a team of researchers has come up with a surprising addition to that list: Remove any light, metal objects from the room that can be seen from a window.
At the Black Hat Asia hacker conference in Singapore in May, researchers from Israel’s Ben Gurion University of the Negev plan to present a new surveillance technique, designed to allow anyone with a Peripherals can eavesdrop on conversations if they can only find their line of sight through a window to any of the many reflective objects in a given room. By pointing an optical sensor attached to the telescope at one of those shiny objects — the researchers tested their technique with everything from aluminum trash cans to metallic Rubik’s cubes — they were able to can detect vibrations visible on the surface of objects allowing them to emit sound and thus hear speech in the room. Unlike older experiment Similar to tracking small vibrations for distant listening on a target, this new technique allows researchers to capture conversations at a lower volume, works with a larger audience, and allows Real-time tracking, rather than post-realistic reproduction of the sound of a room.
“We were able to recover voices from light, shiny objects placed close to the speaker by analyzing the light reflected from them,” said Ben Nassi, professor at Ben Gurion. do research with Ras Swissa, Boris Zadov and Yuval Elovici. “And the beauty of it is that we can do that in real-time, which for espionage allows you to act on information revealed in the content of the conversation.”
The researchers’ trick takes advantage of the fact that sound waves from speech produce changes in air pressure that can vibrate objects in a room imperceptibly. In their experimental setup, they attached a photodiode, a sensor that converts light into voltage, to a telescope; Its lenses have a longer range and the more light that allows them to hit the sensor, the better. That photodiode is then connected to an analog-to-digital converter and a standard PC, which converts the sensor’s voltage output into data representing real-time fluctuations of the light. reflected from any object the telescope is pointed at. The researchers were then able to correlate those small light changes with the vibrations of objects in the room where the person was speaking, allowing them to reconstruct the speech of someone nearby.
The researchers have shown that in some cases, using high-end analog-to-digital converters, they can restore the voice heard by their technique when a person speaks blocks away. The shiny metallic Rubik is about 10 inches and speaks at 75 decibels, the volume of a noisy conversation. With a sufficiently powerful telescope, their method worked to a range of up to 115 feet. Besides the Rubik’s Cube, they tested the trick with half a dozen objects: a silver figurine, a small polished metal trash can, a less-shiny aluminum iced coffee can, an electrical standard. aluminum smartphones and even thin metal blinds.
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Sound recovery is clearest when using objects like smartphone stands or trash cans, and least clear with venetian blinds — but every word can still be heard clearly in some cases. Nassi points out that the ability to capture sound from window coverings is particularly ironic. “This is an object designed to increase privacy in a room,” says Nassi. “However, if you get close enough to the venetian blinds, they can be exploited as diaphragms and we can recover the sound from them.”
Researchers Ben Gurion have named their technique Little Seal Bug in homage to a notorious Cold War espionage case known as Big seal: In 1945, the Soviet Union presented a wooden stamped sign showing the coat of arms of the United States to the embassy in Moscow. Nassi suggests that the Little Seal Bug technique could work similarly when a spy sends someone a seemingly innocuous gift of a metal trophy or figurine, which the eavesdropper can then reveal. exploit as a super spying device. But Nassi argued that it was likely the target had a suitable light shiny object on their desk, under the view of a window, and any optical detectors.
Nassi’s team isn’t the first to suggest that long-range, optical spies could collect voice conversations. In 2014, a team of researchers from MIT, Adobe, and Microsoft created what they call “Visual Microphone” showed that it was possible to analyze a video of the leaves of a houseplant or an empty bag of chips inside a room to detect vibrations and reproduce sound in a similar way. But Nassi says his researchers’ work can pick out sounds that are lower in volume and require much less processing than the video analysis used by the Visual Microphone team. The Ben Gurion team found that using a photodiode is more efficient and effective than a camera, allowing for easier long-range listening to a wide variety of new subjects and providing real-time results.
