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Comment by samsnelling | Hacker News Reader

Thanks for this! I've been looking for more to read (I just went back and re-read 1984).

... I thought one of the points of Fiber was that you couldn't tap in without disturbing the optical signal? Did I just make that up in my head?

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I don't see why that would be true. This is classical signal transmitted optically, not quantum cryptography. There is no reason you couldn't splice the cable through a machine that recorded the signal and then recreated it. Or a beam splitter that removed just a small fraction of the signal; the effect would be a slight increase in transmission loss.

The prevailing theory is that they do the latter; the former would be both easy to detect (at the time of splice) and locate (via TDR).

Getting the signal out of the fiber pales in comparison, though, with the task of getting all of that data back to Maryland/Utah.

Unless they have specific cooperation of the cable owners and can tap/split the fibers at the landings, they must be spending a significant percentage of the cost of the original fiber runs (in parallel cables to return the tapped data). The mind reels.

https://en.wikipedia.org/wiki/USS_Jimmy_Carter_(SSN-23)

Beam splitters don't cause any reflections?

I don't know much about undersea cables (although it is a fascinating subject), but I imagine there's no need to tap a cable in the middle of the ocean. If instead you tap it a couple miles offshore (even tens of miles), suddenly have a lot less undersea fiber to run. And if multiple cables come ashore at the same place, you can probably disguise it as just another fiber.

Of course, this requires a friendly country at one end of the cable, but that's probably not too big a problem.

Yes but there is a problem, other countries also have submarines/boats that protect their assets.

I had a professor who did optics research sponsored by the NSA. They didn't tell him the intended application, but he suspected it was to tap optical fibers by evanescent wave coupling (see http://en.wikipedia.org/wiki/Evanescent_wave#Evanescent-wave... ). It's as if photons are quantum tunneling out of the fiber, so there is no need to physically cut into it. That would have made the tapping nearly undetectable.

I don't believe fibre cables are single length. Between your point of signal origin and the destination are already a number of boxes that act as repeaters. To split the cable, you'd effectively add in another one (or subvert the provider, of course). Or I believe you can tap the cable anyway:

This is a nice primer on fibre:

http://www.redbooks.ibm.com/redbooks/pdfs/sg245230.pdf

And here is one talking about its security, in particular vs tapping (the conclusion: it can be done):

http://www.sans.org/reading_room/whitepapers/physcial/fiber-...

Finally, I always figured that tapping fibre was exactly what this was for:

https://en.wikipedia.org/wiki/USS_Jimmy_Carter_(SSN-23)

> you couldn't tap in without disturbing the optical signal

Well of course you can't. If you're going to split it off to read it, then you're "disturbing" it by definition.

Whether or not you can do such that it's not noticeable to the proper end parties, of course, is a different story.

What's to stop a direct packet copy? The line goes in, a digital device sees the packets, copies them bit for bit and sends the original to their destination and a copy to the NSA. Similar to headphone splitting.

The act of doing the splitting would increase latency.

I'm no expert but this will probably produce extra latency?

I think most of the taps they're referring to involve tapping light directly off the fiber, which reduces the light intensity at the receiving end and can therefore be detected in theory at least

Interfering with existing amplifiers/signal boosters would be fairly hard to hide unless the NSA was solely responsible for that units maintenance, and I suspect that as a general rule they aren't. It's much easier to hide a tap at some random point along the line where nobody has any reason to visit

You're likely thinking of quantum communications: https://en.wikipedia.org/wiki/Quantum_key_distribution

There are different non-disruptive techniques, two known methods being "shaving" the cable and the other involves bending the fiber optic cable at certain angles.

I wouldn't be surprised if there are other esoteric techniques that somehow allow NSA to monitor emanations through an intact fiber optic cable and its shielding.

No, you have not made it up in your head. It has been widely accepted as a fact but I guess if it was originally true there must have been a few "givens'.

Who said this? It seems obviously false. All you would have to do is insert a detector and another emitter that simply replays everything the detector reads.

While I agree it's certainly false, your implementation idea would almost certainly introduce detectable delay. All you'd need is a beam splitter. You can manufacture them to only take 1% of the beam.

Sure. But "Hey guys, just to let you know, we moved our relay back a couple meters for reorganization" would also introduce detectable delay -- I doubt anyone actually cares about the delay.

In the late 90's, I attended a presentation that described doing just such a fractional-light fiber split at major exchanges (e.g. MAE-West) to collect data for research purposes. [1] While the researchers were probably trustworthy, I remember thinking that such sniffing seemed like it could be pretty scary in the wrong hands.

(The presentation was given by Evi Nemeth, who was sadly in the news recently due to being lost at sea.)

[1] http://www.caida.org/workshops/isma/9808/report.html "The coral/ocXmon family of monitors use optical splitters to tap fiber, filtering 5-10% of the light signal to interface cards in the coral monitoring host."

Would such a splitter give you 1% of the messages passed, or 1% of a message?

These splitter work in the domain of light-pulses transmitted over a fiber. So you get 100% of the messages, but the flashes of light representing the bits will be much weaker. Probably this will mean that you have to put in much more effort to decode the signal than a usual network-device will need, and also probably means that you will have a higher number of errors in your data.

On the other hand, if you'd tap only a short distance downstream of the transmitter (or an inline amplifier), that 1% might be plenty, undisturbed by the distortions introduced further on the line, so probably that's the preferable tapping location anyway.

[I know that I'm oversimplifying a lot here and modern optical communication systems work much different.]

It depends on the power budget of the fiber link. A 3db splitter would tap 50% of the power, but if this was planned for in advance it would be easily integrated in the long haul network.

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