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Securing Fiber Using Light Polarization
screenbert writes: "A new and novel way of
communicating over fiber optics is being developed by physicists supported by
the Office of Naval Research. Rather than
using the
amplitude and
frequency
of
electromagnetic waves, they're using the polarization of the wave to carry
the signal. Such a method offers a novel and elegant method of secure
communication over fiber optic lines. This
press release has more information. Of course I always thought that fiber
was always pretty secure anyway since it's a lot harder to tap than copper."
...until polarizaton-based recievers become widespread, anyway.
Security through exclusivity ("It'll be secure, because we're the ONLY PEOPLE who have the hardware to read it!") doesn't work for very long.
Not that it's easy to tap fibers, anyway... Even if you have the equipment, you have to figure out which fiber out of 288 or more is the one you need, and the documentation is usually kept locked up tight.
How do you secure a physical medium from interception? If you intercept a signal, can't you just rebroadcast the same signal back out as long as it was read correctly in the first place? Isn't the real security in the encryption of the data being transmitted over the medium?
"Of course I always thought that Fiber was always pretty secure anyway since it's a lot harder to tap than copper."
Its really not that hard if you want to. The average script kid might not have the money but for corporate espionage its no problem. Just get a fiber capable router or switch. A quick glitch in the transmission and youre in.
HTTP/1.1 400
Help me out here. Polarization modulation is nothing new, right? The trick here is cancelling out the chaotic variations by sending the signal twice and doing the comparison?
I'm asking because the first sentence of the press release makes it sound like these guys invented polarization modulation, and I'm pretty sure I read about that a looooong time ago.
Please donate your spare CPU cycles to help fight cancer and other diseases
"It provides a definite advantage over direct encoding of polarization, leaving an eavesdropper only chaotic static, and no means to extract the signal."
Why the extra security? There's already the depths of the ocean, the difficulty of trying to tap a fiber line, not to mention whatever encryptation they have on their data. They must be looking at some questionable pr0n to go to these lengths.
Job? I don't have time to get a job! Who will sit around and bitch about being broke and unemployed then?
This method is neither new or novel, it's called Quantum Encruption. You can read a quick primer Here. By using polarized photos, you can trasmit bits that will be impossible to intercept without being detected. Research labs have been working on relaible, long-distance implementation for years.
Or... you could use one of the numerous software packages that already exist to "encrypt" your data.
Quantum cryptography uses the polarization of light to transmit provably secure information. The trick is that when you receive polarized light, if you pick the wrong polarization there's a 50% chance that the light will spontaneously flip to that polarization. Thus, unless you know the correct polarization sequence (the key), as you receive the light, you will not be able to intercept the communications under even the best of circumstances.
Q C. htmlr ypto/q uantum1.htm
This isn't exactly new either. Its been around since at least the 70's.
More info:
http://www.cs.mcgill.ca/~crepeau/CRYPTO/Biblio-
http://www.cyberbeach.net/~jdwyer/quantum_c
Because it was harder to tap than string between cans.
Is this the promised end? Or image of that horror? KING LEAR
You know, like blueprints on missiles, corporate finances, medical records and such. There are circumstances where the data must not be interceptable by anyone. Not even the US marine thats been sniffing copper for as long as theres been phone lines. I dont think we will see these things in other than military installations and other places where the data is sensitive.
HTTP/1.1 400
Of course I always thought that fiber was always pretty secure anyway since it's a lot harder to tap than copper
Boy did you think wrong. The USS Jimmy Carter is being retrofitted just for the purpose of tapping fiber optic cable.
Why go through the trouble of intercepting it at the fibre level when we can just intercept it near their WiFi stations?
The central issue is that in most of the inexpensive single mode fibers, there are random rotations of the polarization state as you transmit light down the fiber.
Moreover those random shifts are time-dependent on account of the physical fluctuations in environment of the fiber optic channel.
That makes traditional polarization modulation difficult to do since the receiver has to dynamically track the unknown polarization matrix correpsonding to the transformation, and that is not easy or inexpensive.
This new method obviates the issue by doing polarization modulation in a distinctly new way, wherein the modulation is in the feedback arm of a chaotic erbium doped fiber ring laser. Changes in the modulation (i.e. message being transmitted) is thus fed back into the dynamics of the transmitter somewhat akin to the state of a cypher (though these schemes are not designed or analyzed to resist cryptanalytic attacks)
There are a few things combined as one then: the production of light in high power (EDRFL), chaotic signal masking by transmitting a high dimensional chaotic state, modulation based on dynamical polarization differences. Also, detection methods for polarization usually require "coherent detection" i.e. interferometry with a coherent source (local laser)---those detectors are much more expensive and difficult than amplitude detectors that measure the short term intensity. Greg has previously shown a technique to use the ampltitude only detectors to nevertheless extract the instantaneous (and not time averaged) polarization state on the Poincare sphere so I expect such techniques to be used in this paper as well.
Just polarization differences via time-delay doesn't work either if you don't have a chaotic underlying carrier as too many things cancel.
I previously collaborated with the two of them on chaotic communication in fiber ring lasers; we derived simulations of the equations of motion and amplitude modulation in the chaotic state. They published experimental results on amplitude modulation in a similar setup before.
Well, er, not exactly.
The technique described in the press release describes a technique for hiding a polarization modulation signal in the polarization state noise inherent in the ring laser system the experimenters used. It's clever, but it's very much not quantum encryption. In principle, it would be possible to siphon a few photons off the fiber and squeeze information out of them, though it would be very difficult. Quantum encryption, as described in the article referenced in the parent post, is a very different technique. It relies on measurements of the polarization states of single photons, not continuous beams. It is immune to (undetected) interception, because tapping the beam irretrievably loses some data (hooray for quantum mechanics.) It is not well-suited to fibre systems--it's difficult to push single photons down a fibre and reliably measure and retain their polarization. It would excel, however, for communcations that could take place over line-of-sight spans, even very long ones.
~Idarubicin
Bruce Schneier gives a good overview here.
The table of contents is here.
their "descrambling" method doesn't sound hard - you take the light you receive and send half through a delay loop equal to one circuit through the originating ring laser. then you compare the two signals to obtain the data.
the only eavesdropper this will thrwart is the guy who uses only intensity (and not polarization) measurements. communication using "Polaritons" has been around for a while.
the easy way is to put your light through an birefringent crystal and modulate the input voltage - this produces a change in the polarization you can read out with a simple polarizer. the problem is, when you try to change the phase on a photon fast (like for data transfer), you screw up the frequency. and by screwing up the frequency you reduce the gain of your doped fiber amplifiers and you crowd signal space for other colors (although not much, admittedly).
conclusion: this is useless for sending obscure data. hiding your data in noise is useless if everyone knows how to remove the noise.
muerte
As for knowing what fiber goes where, again, good luck getting the info. I worked for a fiber optic mapping company for some time (hence why I'm posting AC), I've seen some of the maps and info the companies have for their -own- networks. Many companies are in the process of digitizing their maps, but most often the ones they have now are paper, fairly cryptic, with only one/two people really being 'in the know' as to what they mean, per. region.
Thats the theory behind quantum encryption, in which single photons are used to create a shared key by playing tricks with polarisation. The important point is the words "single photon".
However QE cannot work over long distances because photons get lost (i.e. attenuation). General purpose signalling sends a lot of photons so that at least a few get through (I think the detection level for general purpose detectors without special cooling is around 70 photons). They also get amplified. I'm not sure if fibre amplifiers maintain polarisation. If not then this technique is just an interesting novelty.
So tapping would be easy. Just put the signal through a splitter (e.g. a bend in the fibre) and route your half of the signal to a decoder that works in the same way as the official one. The other end sees a 3dB drop in signal, but thats probably too small to be noticed.
Where this might be important is increased bandwidth. At the moment fibre transmission uses binary keying: send photons for 1, no photons for 0. Polarisation modulation means that you could use several different angles, and hence encode more than one bit per light pulse.
But don't get too excited about the bandwidth either. The limiting factor on bandwidth at the moment is the routers at the end of the fibre. We can pump terabits down a fibre in the lab, and 100 Gbit is pretty straighforward to do in the field. But put ten 100Gbit links into a router and you have to have a machine that can switch 1 Tbit. If the average packet is 1.5kbytes (Ethernet frame) then thats around 83 million packets per second. Even with hardware assist thats an awful lot of address table lookups per second.
Paul.
You are lost in a twisty maze of little standards, all different.
all signals are noise if you don't know how to filter it.
The Kruger Dunning explains most post on
Making the wire hard to tap is useless when you're in the military. Once something is in widespread enough use SOMEONE will make a tool for breaking it. I'm sure there's a "fiber tapping kit" out there that every government uses some variant of. It might be hard, but it's not impossible, and that means it's going to be done.
I wonder why people can't get even the VAGUE details right.
The modifications to the JIMMY CARTER are being done in new-construction, a modification to SEA WOLF design. It's an expensive change, sure. But it's not a retrofit. What PARCHE got was a retrofit.
Can someone more versed in optics explain to me why you can't just use FTIR (picking up the evanescent wave) to tap into a fiber without actually splicing it? It seems like it should be possible, and you wouldn't have to damage the fiber except for removing the cladding...
not really. it's just that you're more comfortable
with a soldering iron than a butt-polisher.
i readily admit that an optical amplifier has at
least one more stage than an electrical one, but
c'mon, that's just one more component on a circuit
board, if you're using an ASIC for the core.
being less popular doesn't really mean it's
*harder*. but i confess it does mean the
probability of tap is lower.
But doesn't everybody use crypto for sensitive
data? That being the case, physical vulnerability
is down in the noise. Spend your time and money
on key management instead, and you'll be safer.
At least until those quantum well devices start
coming out...
-I like my women like I like my tea: green-
I must really be missing something here, because I don't see how the polarization plays any important role in securing the transmission.
It seems to me that you could do the same thing with ANY modulation mode: just mix two copies of the signal, one delayed by 239-nanoseconds apart, with a noise background, and extract the signal by correlating it against a 239-nanosecond-delayed version of itself.
Seems like a fairly weak kind of encipherment, since all you need to know is what kind of modulation has been used and what the delay is.
Seems to me that even the kinds of ciphers I used to read about in junior high school (Vigenere, etc.) would be just as secure if not more.
I don't see much security just from a novel means of modulation. I mean, sure, if all anyone has are FM receivers you can send secret messages by using AM modulation. And an ordinary 2400 bps modem is pretty secure if all you can do is listen to it with the naked ear...
"How to Do Nothing," kids activities, back in print!
It's a clever technique. Essentially, it's crypto
in which the key is the ring radius. But the
time to defeat for reasonable ring sizes will not
be very great. Still, it's a good hardening layer
on top of conventional cryptography.
-I like my women like I like my tea: green-
How long till speculating on the means are punishable? This shit's not rocket science. Get the fiber, make a tiny scratch in the suface. Focus a detector on the scratch as it reflects the signals. You are done. As for the polarized gadget, it looks like you might have to set up a beam splitter and figure out how many angles they have set up. It's more complicated by not impossible.
Of course, all of this has the ring of Big Brother's underground mole invasion device. Why would you go for a calble under the sea when you could just tap a silly desktop or phone line of interest instead? Kind of like traveling underground when you could just fly. Your tax dollars at work! Buy your 2.4 billion dollar submarine and tap cables today.
DMCA, Hollings, Palladium. What might have sounded like paranoia is now common sense.
I have a question on that anyway.
I know you can't put a quantum crytography signal through an EDFA, thus making lots of copies of the signal photons and giving you enough chances to beamsplit and measure the polarisation states.
How do I know this? Because it wouldn't be a good system if you could. What I want to know is why doesn't this work? What fundamentally stops this happening?
It can't be that Eve might NOT split off all but one of the amplified bunch of photons for any individual bit and thus giving the game away to Alice because Eve could just retransmit from scratch.
Is it instead something about the beamsplitting process? I seem to remember a presentation at Uni from one of the theory guys which implied that 2 identical photons (such as the original and a copy out of an amplifier) are not independantly beamsplit but that instead take to reflection or transmission output path from the beamsplitter as a pair.
Is that right? Or is it something else entirely.
If there is anyone who can reply, that would be great. I know all the experimental side of these things, I built Erbium fibre ring lasers and looked at their output polarisation states for my PhD. I just don't have the quantum theory knowledge.
It looks like if the cable it tapped, the other end will know about it. That is moreimportant t than encrypting the dataflow.
:-) I would take a guess that it would only take about 6e25 vector calcs per bit change so about the same as 80 bit encryption per bit.
Years ago I looked at doing a type of computer generated hologram. It involved something like ray tracing backwards. So instead of 1024x768 pixels and figuring out where the light went, you had a 1024x768x10k and you had to backtrack the other way and add up all the wave interference. Looks to me like you could throw in one more axis for polarization to this system and you'd have it cracked in no time --assuming you do the all the calculation in no time