A technique called lamphone allows for real-time listening in on a room that's hundreds of feet away.
Before now, there have been many techniques used to eavesdrop or spy on people. They include hacking their phones or planting bugs in the homes of people. It has even been once reported that bouncing lasers off of a building’s glass could be used to eavesdrop on conversations. But now researchers have just revealed yet another technique that involves the use of light bulbs visible from a window. Yes, a light bulb. It sounds impossible, right? Like one of those sci-fi or action movies where spies use crazy gadgets to spy on individuals. Yes but this is actually real and possible.
The researchers are from the Israeli’s Ben-Gurion University of the Negev and the Weizmann Institute of Science today. And they are calling this new technique “lamphone.” They claim anyone with a laptop, a telescope and a $400 electro-optical sensor will be able to use this technique to listen in on sounds in a room that’s miles away. And all it takes is to observe the minuscule vibrations those sounds create on the glass surface of a light bulb. By measuring the little changes in light output from the bulb that those vibrations cause, the researchers show that a spy can pick up sound clearly enough to discern the contents of conversations or even recognize a piece of music.
Ben Nassi, a security researcher at Ben-Gurion developed the technique with fellow researchers Yaron Pirutin and Boris Zadov. Together they plan to present their findings at the Black Hat security conference in August.
“Any sound in the room can be recovered from the room with no requirement to hack anything and no device in the room, you just need line of sight to a hanging bulb, and this is it.” says Ben Nassi
During their experiments, the researchers placed series of telescopes about 80 feet away from an office’s light bulb. They palced the eyepiece of each telescopes in front of a Thorlabs PDA100A2 electro-optical sensor. After which they converted the electrical signals from that sensor to digital information by using an analog-to-digital converter. While they played music and speech recordings in the faraway room, they fed the information picked up by their set-up to a laptop, which analyzed the readings.
The researchers discovered that the produced sound caused little vibrations of the light bulb, and the vibrations were registered as measurable changes in the light their sensor picked up through each telescope. They processed the signal through software just to filter out noise, after which they were able to reconstruct recordings of the sounds heard from the room with fidelity: They revealed, that they could reproduce an audible snippet of a speech from President Donald Trump well enough for it to be transcribed by Google’s Cloud Speech API. They also generated a recording of the Beatles’ “Let It Be” clear enough that the app Shazam could instantly recognize it.
However, as you might have guessed, the technique has some limitations. In their experiments, the team used a hanging bulb. And they are not yet sure if a bulb mounted in a fixed lamp or a ceiling fixture would vibrate well enough to get the same kind of audio signal. Also, in their experiments, the voice and music recordings they used were louder than how the average human conversation would be. Nonetheless, they pointed out that they also used a cheap electro-optical sensor and analog-to-digital converter, and upgrading to more expensive ones could pick up more quiet conversations. LED bulbs also offer a signal-to-noise ratio. Which is about 6.3 times that of an incandescent bulb and 70 times a fluorescent one.
Irrespective of those little limitations, Dan Boneh, a Stanford computer scientist, and cryptographer argues that the researchers’ technique still represents a significant and potentially practical new form. Of what he calls a “side-channel” attack (one that takes advantage of unintended leakage of information to steal secrets)
“It’s a beautiful application of side channels. Even if this requires a hanging bulb and high decibels, it’s still super interesting. And it’s still just the first time this has been shown to be possible. Attacks only get better, and future research will only improve this over time.” Boneh says.