A research paper produced by researchers at Israel’s University of Negev and Weizmann Institute of Science has revealed hackers can use an innovative technique to eavesdrop on private conversations by tracking vibrations in a lightbulb.
The technique, which the researchers dub “Lamphone”, works by intercepting vibrations in lightbulbs produced by changing air pressure created by sound. The researchers who captured the vibrations and turned them into audio claim they were able to listen to conversations from up to 25 meters away.
"We show how fluctuations in air pressure on the surface of the hanging bulb, which cause the bulb to vibrate very slightly, can be exploited by eavesdroppers to recover speech and singing, passively, externally and in real time," the paper states.
The technique relies on three technologies - a telescope, which is placed in the field of view on the hanging bulb from a distance, an electro-optical sensor mounted on top of the telescope, and a sound recovery system to capture the sound and process it.
When a conversation takes place in a room, the sound creates fluctuations in the air pressure on the surface of the blub, causing it to vibrate - the analog electro-optical sensor then captures this vibration as an optical signal and processes it using an audio recovery algorithm.
"We evaluate Lamphone's performance in a realistic setup and show that Lamphone can be used by eavesdroppers to recover human speech (which can be accurately identified by the Google Cloud Speech API) and singing (which can be accurately identified by Shazam and SoundHound) from a bridge located 25 meters away from the target room containing the hanging light bulb," the study authors say.
Because Lamphone only requires light vibration for capturing the audio, it doesn't necessitate the victims' direct engagement - one major drawback to the technique, however, is it requires a direct ‘line of sight’ to the lightbulb, within 25 meters. Nonetheless, employing telescopes with different lens diameters might allow the technique to function from farther away, it’s alleged.
Still, one way to counter a Lamphone attack would be to use weaker bulbs that emit less light, in the process limiting light captured by the sensor, according to the report. Another is by reducing the vibration with the help of a heavier bulb.
"There’s less vibration from a heavier bulb in response to air pressure on the bulb's surface. This will require eavesdroppers to use better equipment (e.g. a more sensitive ADC, a telescope with a larger lens diameter, etc.) in order to recover sound," the researchers conclude.