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Quantum leap for uncrackable code

The new system fits into two desktop boxes, connected to each end of a fibre optic cable (pic: id Quantique) 新的系统被安装在两个小盒中,中间用玻璃纤维电缆链接 (图片: id Quantique)

A Swiss company has set a world record with a secure communication system, which can operate without fear of eavesdroppers.

This content was published on July 23, 2002 - 11:53

id Quantique, a Geneva University spinoff, sent a totally safe message over the standard telephone network between Geneva and Lausanne - a record-breaking distance of 67 kilometres.

The company uses quantum cryptography, a technique based on single photons of light, which allows users to tell if their data has been tampered with.

The experiment suggests that quantum cryptography is finally ready to move out of the laboratory and into the real world.

"It's a revolution in the way you look at security because you don't base the security of your communications on mathematics anymore but on the laws of physics," said company co-founder, Grégoire Ribordy.

Secret key

If two people want to have a secure conversation, they must first transmit a secret key for encoding and decoding their transmissions.

As long as the key remains secret so does the message. The problem is knowing whether anybody else has intercepted the "key".

Quantum cryptography gets around this problem by using single photons for transmitting the key. The system's security is based on the fact that anyone hacking into a message automatically changes the particle's quantum properties.

The interception introduces errors into the transmission so that the receiver knows that the key is unsafe.

Until recently, the photon detectors required a large liquid nitrogen cooling system. "We miniaturised the whole detector system and use a different type of cooling system," Ribordy told swissinfo.

The new system can be fitted into two desktop boxes, connected to each end of a fibre optic cable. Each box contains a laser for generating single photons, a device for encoding information on to each photon and the detector for sensing photons when they arrive.

Commercial system

Ribordy said the technology was now mature enough to be applied in a commercial product but he acknowledged that it had one major drawback.

The system has a distance limitation of around 70 kilometres because of the attenuation in optical fibre.

"Of course if you limit the distance to 60-70 kilometres it means that the range of applications will be more limited," he said.

"One can imagine, for example, communication between different bank buildings in a metropolitan area but we will not be able to secure communication between Paris and New York in the short term."

Meanwhile the company is already selling its quantum random number generator.

Random numbers are essential when a company issues credit cards or otherwise needs to ensure secret transactions online.

"The interesting thing about using photons is that it is the only system to give you true random numbers," said Ribordy.

by Vincent Landon

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