February 7, 2006 4:00 AM PST

NSA eavesdropping: How it might work

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If the participating companies developed cold feet because of congressional scrutiny or class-action lawsuits, however, the NSA could conduct land-based wiretaps without the companies' participation, consultant Chovanak said. "There are things you can do without working with the providers," he said. "Every six miles on a fiber, there are tap points, and about every 50 miles there are repeaters, which are frequently going to be located in a small building in the middle of nowhere."

Tapping fiber a tricky business
Another option is more clandestine: listening in on a fiber-optic cable without inside help. For many years such a feat was considered to be virtually impossible--mainly because the strands of fiber are so fine that any tampering might disrupt the signal and prevent it from arriving at its intended destination.

That can be done by bending the fiber, to cause some light to leak, or by physically splicing into it. "It's very hard to do that without the recipient realizing the signal is being intercepted," said Corning's Jay, who estimates that it's difficult but not impossible. "It's hard to do without breaking the fiber... It's hard to imagine doing that in a way that doesn't greatly risk damaging the fiber."

Tapping copper cables, on the other hand, is far easier. When a phone wire or other electrical conductor carries a current, an electrical field is generated around the conductor. It's possible for a sufficiently sensitive device to measure the fields without actually splicing into the metal of the conductor. (Optical fiber doesn't generate electrical fields.)

Shade, the WildPackets engineer, said that "fiber-optic splitters are readily available on the commercial market." But he cautioned that any would-be eavesdropper must be extremely careful not to break the fiber strands.

"I think that's where a lot of the perception that fiber is untappable came from, was the difficulty of successfully handling the fiber without breaking it or seriously degrading its performance, because fiber is very temperamental," he said. "It's not like good old phone cable that you just throw down on the ground."

Experts say such a task requires extreme skill. "I would put myself on the side of those who say it's not so easy" to splice into fiber cables, said Ira Jacobs, a professor of electrical engineering at Virginia Tech. "I can access the individual fiber, I don't have to break the fiber and physically put in a tap. If I bend the fiber, I can get some leakage, but I have to access the fiber, I have to strip away other parts of the cable. It is not easy to do in a nonintrusive way."

The difficult task of underwater tapping
Tapping fiber cables while they're underwater transforms an already delicate process into one requiring exquisite surgical precision and skill.

The Wall Street Journal reported in May 2001 that the Navy had decided to spend 5 years and $1 billion to retrofit the USS Jimmy Carter submarine to make it capable of conducting fiber taps on the high seas. Specialized surface ships used by cable companies to repair breaks already have such facilities.

Making that task even more difficult is the high-voltage electrical cable that accompanies the fiber core and powers signal amplifiers dotted along the floor of the ocean. If water touches the electrical conductor during the splicing process, it could cause a huge short-circuit and set off alarms.

"You've got high energy in that fiber, so the capsule that the submarine uses is specifically designed to insulate the piece of cable that's being worked on and allows them to more effectively work on the power cables that are off limits," said Seth Page, the chief executive of Oyster Optics, which sells products to protect against optical tapping. "Because the last thing you want to do is accidentally open a power cable."

That's why the NSA probably reserves underwater, submarine-based tapping for cables that do not make landfall in the U.S.--such as the one linking the Middle East with India and Pakistan, Page believes. Underwater taps "can definitely happen, and I guarantee you it does happen from a higher level military point of view, such as for sensitive information coming out of China and Russia," he said.

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