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Monday, 13 October 2008 07:22

Viennese waltz - first live quantum key distribution network demonstration - UPDATED

In a significant advance for information security science, the first live quantum key distribution (QKD) network was just demonstrated in Vienna at the SECOQC Demonstration and International Conference.

When you start delving into quantum cryptography (quantum encryption), you're entering a world replete with concepts very unfamiliar to most of us.

As Wikipedia explains: "Quantum cryptography, or quantum key distribution (QKD), uses quantum mechanics to guarantee secure communication. It enables two parties to produce a shared random bit string known only to them, which can be used as a key to encrypt and decrypt messages.

An important and unique property of quantum cryptography is the ability of the two communicating users to detect the presence of any third party trying to gain knowledge of the key.

This results from a fundamental part of quantum mechanics: the process of measuring a quantum system in general disturbs the system. A third party trying to eavesdrop on the key must in some way measure it, thus introducing detectable anomalies."

Sort of like an extension of the uncertainty principle from the earliest days of quantum physics in the 1920s and 1930s, usually associated with the name of German theoretical physicist Werner Heisenberg?

No theoretical physicist am I (nor yourself, most likely), but it's all very thought-provoking. However, there's oodles of opportunity for both minor and major misconceptions.

One trap is the misuse of terms, such as the so-called observer effect (that the very act of observation will in itself make changes to the phenomenon being observed). This applies not just on the subatomic scale but also on the gross level. Thus, measuring an electric current can only be done by connecting an ammeter to the circuit thereby drawing an extra amount of current, and measuring a web server's throughput or response times or counting web page hits involves using extra code that slows down that server.Tony Austin's disappearing quantum cat!

Then there's a famous thought experiment known as Schrödinger's cat in which it seems the cat is supposedly neither alive nor dead until observed. (In contrast, some politicians seem to remain dead even after being observed.)

However, most quantum physicists, in resolving Schrödinger's seeming paradox, now understand that the acts of 'observation' and 'measurement' must also be defined in quantum terms before the question makes sense.

In a similar vein, I hereby propose a corollary of the observer effect: Austin's theory of OS euphoric illusion. This states that if you extol the virtues of a particular operating system —such as Windows Vista or Ubuntu Linux— long enough, your sense of reality diminishes to the point where you cannot measure or appreciate the good points of any competing OS, and you get snared in a feature-list trap where you are compelled to build lists of OS features that asymptotically approach infinite length.

When you're moving in such esoteric levels of theoretical physics, it's ever so easy to wander off the beaten track and finish up in a land of absurdity, real Alice in Wonderland stuff, but splendid entertainment nevertheless.


Putting aside diversions like the cat that isn't really there (or is it?), a lot of serious work continues to be carried out in the field of quantum physics, as applied to computing and networking.

As with all pure and applied scientific endeavours, there will be periods of steady progress —sometimes grindingly slow, like Edison's drawn-out experimentation to develop a filament for electric light bulbs. There will be failures, and frustrating dead ends. Then will come a spectacular breakthrough.

The field of quantum cryptography is a special case of quantum computing, which relates to general-purpose computation "that makes direct use of distinctively quantum mechanical phenomena, such as superposition and entanglement, to perform operations on data. In a classical (or conventional) computer, information is stored as bits; in a quantum computer, it is stored as qubits (quantum binary digits)."

"The basic principle of quantum computation is that the quantum properties can be used to represent and structure data, and that quantum mechanisms can be devised and built to perform operations with these data."

Currently it's all rather obscure stuff, and rather difficult for the non-specialist to understand. Sooner or later it's likely to bear fantastic fruit, it's only the timing that's uncertain.

In Vienna last week, the SECOQC - Development of a Global Network for Secure Communication based on Quantum Cryptography project held a QKD network demonstration and conference.

The SECOQC say that it was the first QKD demonstration, but I see from ScienceDaily something that I can't reconcile about their claim: "A joint collaboration between Northwestern University and BBN Technologies of Cambridge, Mass., has led to the first demonstration of a truly quantum cryptographic data network. By integrating quantum noise protected data encryption (quantum data encryption or QDE for short) with Quantum Key Distribution (QKD), the researchers have developed a complete data communication system with extraordinary resilience to eavesdropping."

Then Lijun Ma et al. in Experimental Demonstration of an Active Quantum Key Distribution Network with Over Gbps Clock Synchronization say: "We have demonstrated, for the first time to our knowledge, a complete active three-node QKD secured network, which operates at 1.25 Gbps clock rate and is controlled by optical switches. Using this network, a QKD secured video surveillance system has been successfully demonstrated."

The SECOQC's claim of being first seems to be that they've set up a significant network (six nodes, connected by eight fibre-optic links between Vienna and St Pöelten of over 200 Km combined length), and not just a small-scale experimental one.

Anyhow, it's worth reading the SECOQC white paper on quantum key distribution and cryptography that's designed to allow  comparison of QKD with what is currently offered by classical cryptographic techniques.

"Quantum cryptography and especially Quantum Key Distribution (QKD) has triggered intense and prolific research works during the past twenty years and now progresses to maturity" they say.

"QKD enables secret Key establishment between two users, using a combination of a classical channel and a quantum channel, such as an optical fibre link or a free-space optical link. The essential interest of QKD, that is intrinsically linked to the “quantumness” of the signals exchanged on the quantum channel, is that any eavesdropping, on the line can be detected.

"This property leads to a cryptographic properties (sic) that cannot be obtained by classical techniques; this property allows to perform Key Establishment with an extremely high security standard which is known as unconditional or information-theoretic security. Highly security applications are thus the natural candidates for QKD-based security solutions."


However they warn: "QKD networks are however not ubiquitous networks; they are closed, secret-key-based and distance-limited infrastructures, and their characteristics are intrinsically linked to the quantum nature of their physical layer. As a consequence, such networks fundamentally differ from classical Key Distribution infrastructures and cannot be deployed to secure open networks.

"We however believe that QKD networks are likely to find promising applications in high-security environments that were, up to now, relying solely on trusted couriers for Key Establishment. QKD-based systems can also be considered as an alternative to public-key-based systems for session key exchange in the context of secure networks relying on symmetric-key encryption schemes."

The SECOQC group is hoping to achieve ends like countering espionage, apparently including the Echelon signals intelligence (SIGINT) system run by the "friendly" AUSCANZUKUS signatory states.

Live demonstration of the SECOQC network in Vienna, 08 October 2008.

The picture (courtesy Austrian Research Centers, click on it for an enlargement) shows one of the nodes.

The event was streamed live but unfortunately they didn't take the opportunity record it, which is quite an oversight, so the supplied stream link is dead.

Although these solutions are suitable for some applications such as connecting two data centres in a metropolitan area, they cannot address all scenarios requiring secure communication.

These limitations are related to a number of disadvantages of the point-to-point solutions: the maximum distance between sender and receiver is limited due to loss of photons in the optical fibre; the maximal speed of key generation is relatively low – it is comparable to that of a modem from the 1980’s – and the communication can be interrupted by simply cutting the fibre or interfering with the line of sight (in case of a free-space application).

In a network, longer distances can be bridged and alternative paths between sender and receiver can automatically be chosen in order to increase key generation throughput or prevent denial-of-service attacks even if a communication line is interrupted.

Furthermore, in a network, more than two partners can simultaneously obtain keys for encrypting confidential communication. This development will open up the possibility for telecom operators to develop novel services and products based on quantum cryptography.

If you want to do more reading in this esoteric field, try the International Journal of Quantum Information (IJQI) and get ready to impress your friends by casually dropping lines on such everyday matters as Non-Uniform Mixing Of Quantum Walk On Cycles or On The Non-Existence Of A Universal Hadamard Gate or Generating Quantum Entanglement In Scalable Superconducting Charge Qubits.

Remember that cat from an earlier page? Is it really there, or not? In researching this article, I came across Quantum physics says goodbye to reality where some physicists "giving the uneasy consequence that reality does not exist when we are not observing it."

UPDATE: These physicists are Austrian too. I wonder why so. There must be something in the Austrian water supply that makes them so concerned about reality! You know, Sigmund Freud, and all the rest of them. And what about this village in Austria, does psychoanalysis have its "roots" there? (Australian in joke.)

Until next time, from your sometimes here, sometimes there, unquantifiable iTWire reporter!

Have some fun with a challenge or two that I've devised for you!
Go visit the iTWire TechWords Interactive Crosswords section.


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Tony Austin

Worked at IBM from 1970, for a quarter century, then founded Asia/Pacific Computer Services to provide IT consulting and software development services (closed company at end of 2013). These says am still involved with IT as an observer and commentator, as well as attempting to understand cosmology, quantum mechanics and whatever else will keep my mind active and fend off deterioration of my grey matter.



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