sciencehabit shares a report from Science Magazine: Cold War spies planted bugs in walls, lamps, and telephones. Now, scientists warn, the cables themselves could listen in. A fiber optic technique used to detect earthquakes can also pick up the faint vibrations of nearby speech, researchers reported this week here at the general assembly of the European Geosciences Union. Freely available artificial intelligence (AI) software turned the fiber optic data into intelligible, real-time transcripts. "Not many people realize that [fiber optic cables] can detect acoustic waves," says Jack Lee Smith, a geophysicist at the University of Edinburgh who presented the result. "We show that in almost every case where you use these fibers, this could be a privacy concern."
Fiber optics can pick up on sound through a technique called distributed acoustic sensing (DAS). Using a machine called an interrogator, researchers fire laser pulses down a cable and record the pattern of reflections coming back from tiny glass defects along the length of the fiber optic. When an earthquake's seismic wave crosses a section of the fiber, it stretches and squeezes the defects, leading to shifts in the reflected light that researchers can use to build a picture of an earthquake. DAS essentially turns a fiber cable into a long chain of seismometers that can detect not only earthquakes, but also the rumblings of volcanoes, cars, and college marching bands. And although scientists set up dedicated fiber lines specifically for research, DAS can also be performed on "dark fiber" -- unused strands in the web of fiber optics that runs through cities and across oceans, carrying the world's internet traffic.
DAS can also be used to eavesdrop, the work of Smith and his colleagues shows. They conducted a field test using an existing DAS setup used to study coastal erosion. They set a speaker next to the cable and played pure tones, music, and speech. Human speech contains frequencies ranging from a few hundred to several thousand hertz. The low end of the range could be pulled out of the data "even without any preprocessing," Smith says. "You can easily see acoustic waves." Getting higher frequency speech took a bit of postprocessing, but it was possible. Dumping the data directly into Whisper, a free AI transcription tool, provided accurate real-time transcription. However, this technique worked only for coiled cables, exposed at the surface, at distances of up to 5 meters from the speaker. Burying the cable under just 20 centimeters of dirt was enough to muddy the speech. And straight cables -- even exposed ones right next to the speaker -- did not record speech well.
Fiber optics can pick up on sound through a technique called distributed acoustic sensing (DAS). Using a machine called an interrogator, researchers fire laser pulses down a cable and record the pattern of reflections coming back from tiny glass defects along the length of the fiber optic. When an earthquake's seismic wave crosses a section of the fiber, it stretches and squeezes the defects, leading to shifts in the reflected light that researchers can use to build a picture of an earthquake. DAS essentially turns a fiber cable into a long chain of seismometers that can detect not only earthquakes, but also the rumblings of volcanoes, cars, and college marching bands. And although scientists set up dedicated fiber lines specifically for research, DAS can also be performed on "dark fiber" -- unused strands in the web of fiber optics that runs through cities and across oceans, carrying the world's internet traffic.
DAS can also be used to eavesdrop, the work of Smith and his colleagues shows. They conducted a field test using an existing DAS setup used to study coastal erosion. They set a speaker next to the cable and played pure tones, music, and speech. Human speech contains frequencies ranging from a few hundred to several thousand hertz. The low end of the range could be pulled out of the data "even without any preprocessing," Smith says. "You can easily see acoustic waves." Getting higher frequency speech took a bit of postprocessing, but it was possible. Dumping the data directly into Whisper, a free AI transcription tool, provided accurate real-time transcription. However, this technique worked only for coiled cables, exposed at the surface, at distances of up to 5 meters from the speaker. Burying the cable under just 20 centimeters of dirt was enough to muddy the speech. And straight cables -- even exposed ones right next to the speaker -- did not record speech well.
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