[ISN] First quantum cryptography network unveiled

From: InfoSec News (isn@private)
Date: Mon Jun 07 2004 - 23:56:33 PDT

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    Celeste Biever
    04 June 04 
    The first computer network in which communication is secured with
    quantum cryptography is up and running in Cambridge, Massachusetts.
    Chip Elliott, leader of the quantum engineering team at BBN
    Technologies in Cambridge, sent the first packets of data across the
    Quantum Net (Qnet) on Thursday. The project is funded by the
    Pentagon's Defense Advanced Research Projects Agency.
    Currently the network only consists of six servers, but they can be
    integrated with regular servers and clients on the internet. Qnet's
    creators say the implementation of more nodes in banks and credit card
    companies could make exchanging sensitive data over the internet more
    secure than it is with current cryptography systems.
    The data in Qnet flows through ordinary fibre optic cables and
    stretches the 10 kilometres from BBN to Harvard University. It is
    encrypted using keys determined by the exchange of a series of single,
    polarised photons.
    The first money transfer encrypted by quantum keys was performed
    between two Austrian financial institutions in April 2004. But Qnet is
    the first network consisting of more than two nodes to use quantum
    cryptography - a more complex challenge.
    "Imagine making a phone call. If you just have one possible receiver,
    you wouldn't even need buttons," explains Elliott. "But with a network
    you need a system that will connect anyone on the network to anyone
    else." In Qnet, software-controlled optical switches made of lithium
    niobate crystals steer photons down the correct optical fibre.
    Intruder detection
    Quantum cryptography guarantees secure communications by harnessing
    the quantum quirks of photons sent between users. Any attempt to
    intercept the photons will disturb their quantum state and raise the
    But Elliott points out that even quantum cryptography "does not give
    you 100 per cent security". Although quantum keys are theoretically
    impossible to intercept without detection, implementing them in the
    real world presents hackers with several potential ways to listen in
    One example is if a laser inadvertently produces more than one photon,
    which happens occasionally. An eavesdroppper could potentially siphon
    off the extra photons and decrypt the key, although no one has
    actually done this.
    "However Qnet is more secure than current internet cryptography," says
    Elliott, which relies on "one way functions". These are mathematical
    operations that are very simple to compute in one direction, but
    require huge computing power to perform in reverse.
    The problem is, according to Elliott, that no one has actually proved
    that they cannot be solved in reverse. "So who's to say that someone
    won't wake up tomorrow and think of a way to do it?"
    Large and expensive
    At the moment computers capable of quantum cryptography are large and
    expensive, because they are custom-made. Elliott imagines a Qnet-like
    system may first appear in banks, for whom these factors might be less
    of a problem.
    Another limitation is that, for distances over 50 kilometres, the
    photon signal is degraded by noise, and it is unclear as yet how this
    problem will be overcome.
    However, quantum keys can potentially be exchanged over much larger
    distances through the air. Tiny, aligned telescopes can send and
    detect single photons sent through the air.
    The distance record for this form of transmission is currently about
    20 kilometres. But calculations suggest that photons transmitted
    through the air could be detected by a satellite, which would enable
    data to be sent between continents.
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