Following revelations that both the U.S. and the U.K. spy agencies, the NSA and GCHQ, are tapping directly into the Internet’s backbone, The Atlantic asks: how does one tap into an underwater cable?

The process is extremely secretive, but it seems similar to tapping an old-fashioned, pre-digital telephone line — the eavesdropper gathers up all the data that flows past, then deciphers it later.

More than 550,000 miles of flexible undersea cables about the size of garden watering hoses carry all the world’s emails, searches, and tweets. Together, they shoot the equivalent of several hundred Libraries of Congress worth of information back and forth every day.

In 2005, the Associated Press reported that a submarine called the USS Jimmy Carter had been repurposed to carry crews of technicians to the bottom of the sea so they could tap fiber optic lines. The easiest place to get into the cables is at the regeneration points — spots where their signals are amplified and pushed forward on their long, circuitous journeys. “At these spots, the fiber optics can be more easily tapped, because they are no longer bundled together, rather laid out individually,” Deutsche Welle reported.

But such aquatic endeavors may no longer even be necessary. The cables make landfall at coastal stations in various countries, where their data is sent on to domestic networks, and it’s easier to tap them on land than underwater. Britain is, geographically, in an ideal position to access to cables as they emerge from the Atlantic, so the cooperation between the NSA and GCHQ has been key. Beyond that partnership, there are the other members of the “Five Eyes” — the Australians, the New Zealanders, and the Canadians — that also collaborate with the U.S., Snowden said.

The tapping process apparently involves using so-called “intercept probes.” According to two analysts I spoke to, the intelligence agencies likely gain access to the landing stations, usually with the permission of the host countries or operating companies, and use these small devices to capture the light being sent across the cable. The probe bounces the light through a prism, makes a copy of it, and turns it into binary data without disrupting the flow of the original Internet traffic. [Continue reading…]