Electronics  News 
September 16, 2003    

'Unhackable' data will go far 
By Andrew Woolls-King 
Long distance secure data transmission has moved a step closer with the transmission 
of quantum-encoded data over a distance of 100 km. Researchers claim that the 
breakthrough could make "unbreakable" secure data streams a reality within a few 

A team from Toshiba Research Europe, based in Cambridge, UK, has recently demonstrated 
a prototype system working over 100 km of fibre-optic cable. "As far as we are aware, 
this is the first demonstration of quantum cryptography over fibres longer than 100 
kilometres," says Dr Andrew Shields, who leads the Toshiba group developing the 
system. "These developments mean that the technique could be deployed in commercial 
situations within three years." 

Early adopters include organizations that need to communicate highly sensitive data 
including banks, governments and legal firms. Yet with ever increasing numbers of 
companies falling foul to the malicious activities of hackers, it is likely that the 
market for viable quantum cryptography systems will be huge. 

Until now the biggest barrier to successfully using quantum cryptography has been 
reducing the amount of random noise picked up by the receiving detector (which can be 
positioned at either end of the fibre link) due to photon scattering out of the fibre. 
Indeed the rate of encrypted photons surviving the journey along long fibres was so 
low that they were masked by noise in the actual photon detector and the entire 
transmission process failed. 

But by developing an ultra low noise detector exploiting the latest semiconductor 
technology, the Toshiba team has managed to reduce this noise problem to a viable 
level for long distance transmission. Even if the 100-km distance can't be extended, 
some form of "quantum repeater" could be developed to enable totally secure 
communications over even longer distances. 

Quantum cryptography works by using the "teleportation" of quantum states from one 
place to another using photons as the communication "medium". In practice, two users 
on a fibre-optic network form a shared security key. The secrecy of the key is 
guaranteed by exploiting the wave/particle duality of light meaning that the key does 
not "exist" in any detectable sense until the photons sent from the transmitter 
actually reach the receiver. 

Although a hacker could conceivably intercept the stream of photons en route between 
the sender and receiver, Heisenburg's uncertainty principle dictates that that it is 
physically impossible to read the datastream without disturbing its quantum states and 
thus destroying the message. 

Current encryption approaches rely on algorithm that, no matter how complex, could 
eventually be cracked. With quantum cryptography security instead becomes an 
impenetrable and intrinsic part of the data itself. 

R. A. Hettinga <mailto: [EMAIL PROTECTED]>
The Internet Bearer Underwriting Corporation <http://www.ibuc.com/>
44 Farquhar Street, Boston, MA 02131 USA
"... however it may deserve respect for its usefulness and antiquity,
[predicting the end of the world] has not been found agreeable to
experience." -- Edward Gibbon, 'Decline and Fall of the Roman Empire'

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