This article originally appeared on VICE India.
A recent study by cybersecurity researchers has discovered an absurd way of eavesdropping on conversations—through lightbulbs. A group of researchers in Israel introduced a new technique that allows eavesdroppers to spy on conversations by watching a light bulb hanging in the room from a nearby location.
This technique, dubbed as “Lamphone Attack”, shows that a conversation can be eavesdropped from about 25 metres (82 feet) away if there is a hanging light bulb near the location of the conversation. It works by detecting vibrations produced from bulbs due to the fluctuation of air pressure caused by the sound waves. When the sound waves hit the surface of the room, it triggers small vibrations that can be picked up through an electro-optical sensor focused at the bulb, say the scientists. This can then be used to pick up a conversation.
To achieve this, the setup consists of a telescope to provide a close-up view of the room containing the bulb. The electro-optical sensor is mounted on the telescope to convert light into an electrical current. An analog-to-digital converter transforms the sensor output to a digital signal, and then, a laptop processes incoming optical signals and outputs the recovered sound data.
“Any sound in the room can be recovered from the room with no requirement to hack anything and no device in the room,” said the researchers in their study. “You just need line of sight to a hanging bulb.”
Apart from conversations, they pointed out that the method can also accurately identify songs using Shazam and SoundHound, and were able to reproduce a recording of The Beatles’ Let It Be and Coldplay’s Clocks during their experiment.
This is a type of side-channel attack—a method of hacking a cryptographic algorithm based on the analysis of supplementary systems, and relies on indirect data for the hacking. There have been various other suggestions for eavesdropping sound by analysing sound waves on nearby objects, such as through a bag of chips and windows. But the hackers in the study claim their method to be the most realistic of all.
Their method, however, comes with its limitations as well. The bulb needs to be hanging and should be clearly visible. If there is even a lampshade or a curtain in the way, this eavesdropping method would fail. And needless to say, the conversation needs to happen in the room where the light bulb is situated.
But, this is not the first time a light bulb has been used as a hacking device. In 2019, a hacker demonstrated how they could extract WiFi passwords, along with other valuable data, using just a smart light bulb.
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