Photo via Flickr/CC.
The National Security Agency most likely did not listen to you trudge to work this morning over a series of underground microphones. For all we know, the agency isn’t keeping its ears to the ground, as it were. But it could if it wanted to.
It would be the most ambitious use of what’s known as distributed acoustic sensing. Put simply, DAS systems exploit the very same fiber infrastructure that enables our day-to-day communications. But unlike the sensors and cameras baked into our phones and our computers, both tangible manifestations of the specter of surveillance, the largely untapped power (and potential abuse) of DAS is buried deep underground, virtually unseen. To think, a simple hardware add-on to existing fiber lines can have entire swaths of the telecom grid listening around the clock for anything considered physically out of the ordinary.
This is actually going on right now, albeit by a handful of private campanies specializing in both civilian and law enforcement applications of DAS technologies on land and at sea. So we should not get ahead of ourselves in presuming that Keith “I Don’t Know A Better Way to Do It” Alexander or any other NSA hacks have their ears to the ground. Indeed, of all that’s come to light from the ongoing NSA scandal, perhaps the most chilling revelation lies in the agency’s ability to eavesdrop on conversations by turning even your powered-down phone into a microphone. A sprawling network of NAS-DAS listening posts, with microphones positioned every ten meters along a fiber stretch, is probably still a pipe dream.
But the potential for an entity like the NSA to listen to you trudge to work over a series of underground mics is there. Everything is in place. Using DAS technology, the NSA might add a truly staggering number of listening devices to its global dragnet. The fiber optic cables criss-crossing the Earth, forming the central nervous system of telecommunications as we know them today, from email to texts to phone calls, are not simply the strings through which the NSA can listen to your conversations after flipping your powered-off phone into a microphone. The fiber optic cables criss-crossing the Earth are themselves a giant array of microphones, just laying in wait.
The idea is to pick up low-frequency noise activity—the sonic footprints of an idling car, low-flying drone, or hydraulic fracking rig, say, or even actual footsteps crossing a national border or into restricted property—taking place in otherwise harsh, hostile, or sensitive environments, and to be able to perform this surveillance from very far away. Per The Economist, a DAS system:
…works by sending sharply defined pulses of laser light down the cable. When sounds from above are transmitted through the ground, they cause minuscule vibrations in the cable, which change its light-scattering properties in tiny ways. This can be detected when the pulses are received farther down the cable.
From there, high-speed signal-processing algorithms, which were first developed for submarine acoustic detectors by British defense tech firm QinetiQ, “are used to analyse instantly what the sounds are likely to be,” The Economist reports. For example, here’s what the sound of a pig walking looks like:
via OptaSense
If it calls to mind the brittle spikes that register on a seismograph during small tremors, that’s because distributed acoustic sensing is essentially the art of monitoring very small earthquakes. And it’s all set for scaling up: Existing fiber optic cables, like those laid and maintained by any of the big telecom companies, can with not too much effort and expense be retrofitted with an optoelectronic device for full DAS optimization.
But as mentioned, increasingly new fiber is being laid by private firms like OptaSense and Silixa for the express purpose of DAS. Part of the allure here is that DAS cuts above conventional disturbance sensors, which cannot measure “the strain on the fibre to characterise the full acoustic signal.” That’s according to a field test of one of Silixa’s smart distributed audio sensors carried out by researchers at the Massachussetts Institute of Technology, who added that:
Unlike systems relying on discrete optical sensors the distributed system does not rely upon manufactured sensors and is not limited by a need for multiple fibres or optical multiplexing to avoid optical crosstalk between interferometers.
Which is all to say that taken to its extreme and logical endpoint, DAS technology could conceivably track literally everything moving around on Earth. The sobering prospect is that if it were rolled into the US’s surveillance program, the NSA could potentially keep tabs on the supposedly off-the-grid movements of people who are actually up to no good but, more worringly, also on those otherwise law-abiding folks who think they’ve taken the appropriate measures to skate under the radar on account of not wanting their privacy pissed on.
Secret meet up in the woods with your buddies, no phones allowed? Island rendezvous with your drug guy, no phones allowed? No matter. In the blanketed-enough DAS scheme, you couldn’t hide.
Even still, mention of distributed acoustic sensing has fallen almost entirely silent in a good deal of the original reporting and commentary, a lot of which has been equally scrupulous and thoughtful, on the NSA’s global surveillance apparatus being leaked to the press by former US intelligence contractor Edward Snowden. Even if we should be careful to not start connecting dots that don’t exist, you can’t help but begin to imagine how it could all come together.
https://www.eff.org/files/filenode/att/Mark%20Klein%20Unredacted%20Decl-Including%20Exhibits.PDF
We do know that the NSA scoops up information relayed over telecom’s vast fiber optic networks before dumping it all into its program’s databases. William Binney, a former NSA mathematician, estimates that the NSA is behind something like ten to 20 key telecom switches scattered across the US. AT&T whistleblower Mike Klein gave the Electronic Frontier Foundation a bunch of blueprints and photos, seen above, of one such telecom switch, a hidden room full of fiber splitters that the NSA built at AT&T’s San Francisco facility back in 2006.
“The facilities, including a bank of fiber optic splitters, make a copy of all communications traveling over AT&T’s fiber optic cables connecting AT&T’s network to the Internet,” writes the EFF’s Trevor Timm.
Don’t get too many wild ideas, though. This sort of technology is still quite limited, to the point that a DAS fiber optic cable running however far beneath your barn, or your route to and from the office, can’t pick up a conversation you might have. Besides, as The Economist notes, the cables within buildings like the San Francisco AT&T facility “are typically a tangle of short lengths interrupted by junction-boxes,” thus making DAS in that sort of switch location highly unlikely. A lengthy cable buried outdoors, however, can provide anyone with the know-how and resources “the equivalent of a microphone every ten metres,” The Economist adds.
Talk about a truly seismic shift in the way we’d go about putting one foot in front of the other.
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