Original URL: http://www.theregister.co.uk/2003/06/06/holy_grail_of_crypto/

## Holy Grail of crypto to arrive in three years, say UK boffins

Quantum cryptography taken to new lengths

Posted in Security, 6th June 2003 12:06 GMT

UK boffins have demonstrated unbreakable quantum cryptography over fibre links longer than 100km for the first time.

Researchers at Cambridge-based Toshiba Research Europe say their work paves the way for commercial quantum cryptography systems within three years.

Future development will now be partially funded by the Department of Trade and Industry (DTI). The focus of the DTI initiative, which also includes the University of Cambridge and Imperial College, London, is to build a quantum cryptography system which is secure from every type of hacking.

Potential users of quantum cryptography include any organisation using IT and communications technology to send, receive and store sensitive information - from banks and retailers to central and local Government organisations.

Dr Andrew Shields, who leads the Toshiba group developing the system, said: "As far as we are aware, this is the first demonstration of quantum cryptography over fibres longer than 100km. These developments show that the technique could be deployed in a wide range of commercial situations within a timeframe of less than three years."

Much of the interest in quantum cryptography stems from the fact that it is fundamentally secure. This contrasts with today's code-based systems which rely on the assumed difficulty of certain mathematical operations. Ultimately, quantum cryptography seeks to deliver a method of communication whose secrecy does not depend upon any assumptions.

Quantum cryptography allows two users on an optical fibre network to form a shared key, the secrecy of which can be guaranteed. This takes advantage of the particle-like nature of light. In quantum cryptography, each transmitted bit is encoded upon a single light particle (or 'photon'). The impossibility of faithfully copying this stream of encoded photons ensures that a hacker can never determine the key without leaving detectable traces of their intervention.

Until now, the major constraint on the appliance of quantum cryptography is that these light particles could be scattered out of the fibre.

In theory, this is not critical as only the tiny fraction of photons that reach the other end are used to form the key. In practice, however, the rate of photons surviving long fibres can be so low that they are masked by the noise in the photon detector.

By developing an ultra-low noise detector, the Toshiba team has been able to demonstrate a system working over much longer fibres than achieved previously.

Professor Michael Pepper, joint MD of Toshiba Research Europe, said: "The advance of semiconductor technology allows us to implement quantum effects which were previously thought to be only theory. One can foresee that this is the beginning of a process which will lead to a revolution in Information processing and transmission."

Toshiba announced it breakthrough at thee global Conference on Lasers and Electro-Optics (CLEO) in Baltimore, USA this week. ®

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