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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."
This article (did you read it?) doesn't have anything to do with security through exclusivity. The "signal" is encoded in the chaotic "noise" that occurs in a light "circle" and that noise is subtracted from the total received communication at the receiving end to come up with the "signal" again. The researchers have come up with what I would call a type of quantum interference encryption using light (instead of quantum particles). The encryption exists in the chaos of the system rendering the signal received by an eaves dropper useless.
"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?
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
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.
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.
According to Northern
Telecom, tapping a FO cable requires stripping the cable's plastic outer
sheathing and gaining access to the glass fibers within. "When we enter a
fiber bundle, we have instruments that detect whether a given fiber is carrying
a signal before we cut it," North Telecom stated. "A tap could be
accomplished in much the same way."Tapping an optical fiber relies on a macrobending effect. Bending a
fiber 180 degrees around an 1/8-inch radius forces the contained light signal
to go around a tighter bend than it's capable of traversing without some loss
of light. This light loss can be detected and, given the right equipment,
demultiplexed and decoded.
Get it?
HTTP/1.1 400