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Securing Fiber Using Light Polarization

Posted by timothy on from the gentlemen-sharpen-your-flashlights dept.

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."

5 of 152 comments (clear)

  1. Quantum Encryption by FalconRed · · Score: 2, Interesting

    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.

  2. Info 'bout fiber... by Anonymous Coward · · Score: 2, Interesting
    Fiber is certainly not an easy thing to tap into. Ends of the fiber have to be ground just right for the light to traverse w/o loss. Also, fiber doesn't just 'go down', especially for brief periods of time, most of the time fiber goes down because some yahoo construction worker digs where they shouldn't (or they get bad mapping info, something more common than you'd believe). Many fiber routes are redundant (2 points of entry into a building (in case of yahoo worker previously mentioned), and information travelling both ways along the fiber), but I imagine most organizations who've dropped that much money for fiber (and we're talking thousands to tens of thousands per mile (as of 2 years ago)) keep a pretty good eye on their investments.

    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.

  3. More Secure it ain't by Paul+Johnson · · Score: 3, Interesting
    You cannot [measure] the polarization of a wave of light with out changing it.

    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.
  4. Re:More Secure... by Luk+Fugl · · Score: 2, Interesting


    it'll be secure until anyone with the right
    dosh can get their hands on one of these
    recievers

    Not quite, compare the Enigma encryption machine from WWII. The machine wasn't the encryption, just the device (although the machine itself was quite clever). Without knowing the proper setting for the machine, it was near worthless. The allies had their hands on Enigma for several years before they came up with a cryptanalytic method (kudos to the Poles!) that made the physical machine they had worth something. The encryption is in the signal and noise, not in the machine that reads it.

  5. I know this is NOT Quantum Crypto but.... by rjforster · · Score: 2, Interesting

    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.