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Science

Quantum Cryptography Slowed by "Dead Times" 75

Posted by CmdrTaco from the what-i-call-the-time-before-my-first-cup-of-coffee dept.
coondoggie writes "Researchers at the National Institute of Standards and Technology and the Joint Quantum Institute said today that technological and security issues will stall maximum transmission rates at levels comparable to that of a single broadband connection, such as a cable modem, unless researchers reduce "dead times" in the detectors that receive quantum-encrypted messages."
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Quantum Cryptography Slowed by "Dead Times" More

Quantum Cryptography Slowed by "Dead Times"

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  • Use a cat! (Score:1, Funny)

    by Anonymous Coward
    Then maybe it won't be dead!
  • "Quickly, Bones! Transmit the quantum-encrypted packet!"

    "I can't ... it's DEAD, Jim!"
    • Basically, this translates to 'Engineers, put down the Halo controller and get back to work". Early telephones were nothing to call home about either, now they don't even need wires, are small enough for the dog to swallow, and have settings for any feature you can imagine, except possibly "Stun". (note, I'm not sure about this, as I'm still reading the manual that came with my last phone) Improvements will be made, and in a few years you'll look at your old hyperthreaded multi-core biege box and wonder w

  • I have no clue what this is about (Score:5, Insightful)

    by Wannabe Code Monkey ( 638617 ) on Sunday September 30, 2007 @01:04PM (#20802303)

    I read the summary and didn't understand a single part of it, but it sounded interesting and I though, "The article must explain things better." But after reading the article I still have no idea what is going on. Is there someone else that could maybe help explain what this story is all about?

    • Re:I have no clue what this is about (Score:5, Funny)

      by Anonymous Coward on Sunday September 30, 2007 @01:18PM (#20802387)
      hardware which may or may not exist yet is going to run slowly unless said hardware is improved at some time in the future when it may or may not exist.
      • It's all because the Heisenberg cats are controlling the transmission. They control the horizontal, the vertical, and the outer limits of them there quantum encrypted packets, but all these cats want to do is lick themselves and sleep.

      • Re: (Score:1)

        by n3tcat ( 664243 )
        Should we call this Schroedingers Law of technology?
      • Quantum Vaporware. In fact, isn't vaporware in general a quantum phenomenon? A software maker pre-announces a product, but we are unable to tell if the product actually exists until it is released...

    • Dead time in scientific instruments (Score:5, Informative)

      by confused_demon ( 1161841 ) on Sunday September 30, 2007 @01:48PM (#20802587)
      I've got some clue what's meant by dead time for scientific measurements. Basically, dead time is the amount of time after an event is measured that it takes for the detector system to reset. For example, if you're using a Spectroscopy Amplifier (or another shaping amplifier) dead time comes from two signals coming too close to each other. Shaping amplviers are setup so that a square wave (or a step) would produce a characteristic shape (usually a flat-topped Gaussian shape, or a trapazoid). The purpose of the shaping is to allow for the imperfections in detector to be integrated into a single measurement which is easier to process (signal being generated slowly or slowly getting through prior parts of the circuit). If a second signal occurs while the shaping is still taking place it will be integrated into the output of the shaping amplifier resulting in a garbled output for both inputs.

      The net result is that as you send more and more signals to a spectroscopy system, the dead time increases and eventually you get no output because the electronics are constantly saturated. A well put together system will include a measurement of dead time so you know how many signals you're loosing.

    • Re: (Score:2)

      by mangu ( 126918 )
      Maybe you need a quantum decrypter to understand it...
    • Don't understand? This lolcat will explain everything: http://www.thecheezburgerfactory.com/completestore/128351432363906250OHHAIIcollap.jpg [thecheezbu...actory.com]

    • Re:I have no clue what this is about (Score:4, Informative)

      by kmac06 ( 608921 ) on Sunday September 30, 2007 @03:02PM (#20803029)
      Most single photon detectors are a reverse biased photodiode. When a photon strikes it, it creates an electron-hole pair, which then collide with other electrons creating more pairs, making an avalanche effect that results in a pulse, indicating a photon. After this pulse, there is some "dead time" before everything is settled down back to its original state. During this dead time, if a photon hits the detector it will not be detected. Typical dead time is about ~50 ns, limiting the device to about 20M counts/second.

    • Re: (Score:3, Funny)

      by TheRaven64 ( 641858 )
      Einstein explained radio like this:

      You see, wire telegraph is a kind of a very, very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? And radio operates exactly the same way: you send signals here, they receive them there. The only difference is that there is no cat.
      Quantum cryptography is the same, the only difference is that the absence of cat may or may not be alive.
    • Dead-time is the period of time in which single-photons detectors are recovering from an avalanche(the process wich amplifies the current induced by the photon), and can not detect another photon. This time was neglible to the speed QKD was being tested, but the researchers now have found that it is a limiting issue with current improvements. It's just that conventional detectors made of silicon are showing to be not useful beyond some transmission speed.
  • You changed the outcome by measuring it!
  • How can you have security issues with quantum tech?

    Anyone would think this whole industry was smoke and mirrors.

    Additionally, isn't it possible to multiplex the connections and gain parallel speedups?
    My current understanding of quantum tech is the data still goes by traditional means but they use a quantum *handwaving* thing to ensure the bits sent traditionally haven't been messed with.

    • Re:How can you have security issues? (Score:4, Funny)

      by ScrewMaster ( 602015 ) on Sunday September 30, 2007 @01:55PM (#20802623)
      but they use a quantum *handwaving* thing to ensure the bits sent traditionally haven't been messed with.

      It's a Force thing. The quantum circuits say, "you don't need to see his information" and anyone trying to listen in simply waves the information on its way.

    • Re: (Score:2, Informative)

      by SocratesJedi ( 986460 )

      My current understanding of quantum tech is the data still goes by traditional means but they use a quantum *handwaving* thing to ensure the bits sent traditionally haven't been messed with.

      It works under a simple principle: Bits coming down a traditional wire from Alice to Bob can be intercepted by Eve, read and then re-generated down the wire so that neither Alice nor Bob know that Eve has read the message. Quantum cryptography exploits a property of a quantum system that says that if you measure a system: (a) you change the system and (b) you can't get all of the original information about the system back out [think Heisenberg Uncertainty Principle: if you know position accurately, you do

  • meta (Score:5, Insightful)

    by TheSHAD0W ( 258774 ) on Sunday September 30, 2007 @01:08PM (#20802327) Homepage
    So use the quantum cryptography to exchange a large classic private key.

    • Re: (Score:2)

      by Ctrl-Z ( 28806 )
      Why? Who cares if you can exchange keys safely if the cryptosystem is broken?

      • Why? Who cares if you can exchange keys safely if the cryptosystem is broken?
        The solution is simple: Use a non-broken cryptosystem.
        • OK, lets see your algorithms, which cannot be defeated by quantum computing.

          Oh, harder than it sounds, isn't it?
          • AES-256 is thought to be quite indifferent to quantum computing. It's mostly the regular asymmetric algorithms that are targeted by quantum computing.
          • Three words: One time pad.

            It seems to me that this is exactly the type of encryption the GP was referring to when he referenced a "private key." In any case, there already exists unbreakable[1] encryption through OTPs. The problem is coordinating them between parties, which is the problem public-key encryption solves. If (in this case through quantum crypto) we can safely transmit OTPs, we can have perfectly secure communication over any channel of our choosing.

            [1] "...if the key is truly random, nev

      • It's really only cryptosystems with public/private key combinations which are subject to quantum analysis. "What two numbers multiplied make up this number?" This is the sort of question best posed to a quantum computer. Trying to do redundancy analysis on a high-grade key, even with a quantum computer backing you up, isn't going to work very well.

    • Re: (Score:3, Informative)

      by itsdapead ( 734413 )

      So use the quantum cryptography to exchange a large classic private key.

      AFAIK that's basically how it works - the quantum link can't transmit any actual "information" - it just allows Alice and Bob to exchange a big random number in a way that allows them to detect whether Eve is listening in. Even that requires a "conventional" information link and several rounds of back-and-forth commuinication to "agree" on the key.

      I guess the other problem is that to be 100% guanranteed uncrackable the key needs to

      • AFAIK that's basically how it works - the quantum link can't transmit any actual "information" - it just allows Alice and Bob to exchange a big random number in a way that allows them to detect whether Eve is listening in

        A Britney song is just a big random number, and Alice could be RIAA and Bob could be the Britney fan, and this technology will allow RIAA to know if Bob is siphoning off data to an un-DRM'd format such as MP3. Expect to see millions of dollars pouring into this research soon.

        • A Britney song is just a big random number

          I know it is a depressing thought, but no - its not random, its pre-determined. However, any random number could be a Britney song (if an infinite number of monkeys can type the works of Shakespeare then Britney should be a cinch!) so any random number generator is a potentially infringing device under the DMCA.

          If God does play dice with the universe he better not roll the HD-DVD encryption key...

  • Is this really a problem? (Score:1, Informative)

    by Anonymous Coward
    Most of these implementations (like http://www.idquantique.com/products/vectis.htm [idquantique.com]) use quantum mechanics only for key exchange and not for generating a one time pad.

  • Organization often confussed with... (Score:5, Funny)

    by Nezer ( 92629 ) on Sunday September 30, 2007 @01:29PM (#20802469) Homepage
    It should be noted that the Joint Quantum Institute does *entirely different* research than the Quantum Joint Institute located in Amsterdam.

    • Re: (Score:1, Funny)

      by Anonymous Coward
      It should be noted that the Joint Quantum Institute does *entirely different* research than the Quantum Joint Institute located in Amsterdam.

      The latter, presumably, conducting most of their meetings in coffee shops.

  • Comment removed (Score:3, Informative)

    by account_deleted ( 4530225 ) on Sunday September 30, 2007 @01:31PM (#20802481)
    Comment removed based on user account deletion

  • Amazing! (Score:2, Insightful)

    by neiko ( 846668 )
    Quantum transmission speeds will be slow until someone figures out how to speed it up.

  • Tell God you support Quantum Neutrality (Score:2, Funny)

    by Anonymous Coward
    That fucker is just trying to throttle bandwidth unless the matter-energy providers and Waveform Collapsing Union pay his exorbitant Higgs access fees.
  • ...spooky action at a distance and breaking the speed of light barrier. ;-)
  • It sounds to me like they mean:
    The read latency of the quantum receiver is/will be too high.
    Hence throughput speeds will be limited.

    Therefore someone should find a way to reduce this latency, such that transmission speeds can be increased.

  • store it (Score:3, Interesting)

    by Arthur B. ( 806360 ) on Sunday September 30, 2007 @03:04PM (#20803033)
    If you plan to be sending encrypted data to someone, you can exchange a one time pad the size of the data through the quantum channel. When you need to communicate, just use the one time pad at a speed not limited by quantum cryptography.

    You can continuously refill this one time pad thus the real limitation is
      - your average rate of encrypted data over the year
      - disk space (but that's very cheap)

    peak speed of encrypted data transmission is not constrained
    • With quantum cryptography you can read data off the link, but by reading it you change it.
      So someone could read the whole one time pad and decrypt it as it's sent via conventional means, and the person receiving wouldn't know the one time pad had been read until they had the incorrect encrypted message.

      You could checksum the random pad, but it doesn't inspire much confidence. (I'm only barely starting quantum physics in uni so I'm a layman)

  • Amazing... (Score:1, Offtopic)

    by packetmon ( 977047 )
    You know, I'm glad someone explained this all. Critical network and security functions through a flexible content driven, media friendly derivative with parallel facing vector approaches which may or may not be hindered by dead times. This is an extremely proficient alternative to the traditional approach of deploying modular - forward facing designs and parallel vectors. The ramifications of parallelizations are altogether to high to ignore. So yes, I didn't understand it either. Did you?

  • We demand an immediate release of the cat (Score:4, Funny)

    by 140Mandak262Jamuna ( 970587 ) on Sunday September 30, 2007 @03:15PM (#20803093) Journal
    The Society for the prevention of cruelty to Animals vehemantly condemns subjecting animals to needless cruelty in the name of scientific experiments. Release Schrodinger's Cat Now!

  • AFAIK, there are no quantum computing algorithms that do more than effectively halve the effective key length for symmetric key cryptography (things like AES, DES and Blowfish). This means that if you use quantum cryptography to exchange symmetric keys, you should then be able to continue on using these kinds of ciphers in a normal communications channel.

  • Quantum encryption is to be slowing unless some is to be speeding it up.
  • I guess that explains the horrible connection speeds at the county cemetary.....

    Ok. Ok. Ok..... Mod -1 BadJoke

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