If the Yugoslavian forces could intercept and decode messages sent from NATO aircraft, no mission would be successful. One of the technologies that stops sensitive information from falling into the clutches of the enemy is encryption - scrambling digital information so that it is rendered useless to eavesdroppers.

But today's encryption techniques are breakable and it is only a matter of time before someone somewhere develops a computer powerful enough to crack even the strongest encryption.

IBM, British Telecom, Nippon Postal and Telegraphs and the US Department of Energy are separately developing systems that use quantum physics to overcome this problem and provide tamperproof encryption.

Current encryption techniques use the mathematical difficulty of factoring very large numbers to provide security. So while today's computers are good at multiplying numbers, they are not good at performing the reverse of that process: factorisation. So when A sends a message to B they also send a key with the factorisation algorithm, the mathematical formula, or key, which will enable B to decrypt the message.

However, as computers become more powerful the process of factorisation without a key will become easier.

"So much . . . depends on secure communications - from launching of missiles to buying petrol with a credit card," said Dr Richard Hughes, quantum information team leader at US Department of Energy's Los Alamos National Labs in New Mexico.

"The security of quantum encryption relies on a cracker's ability to break the laws of nature rather than circumvent mathematical difficulty."

The computer industry is moving at an alarming rate - what is mathematically difficult today becomes commonplace tomorrow. For example, until very recently, the popular standard encryption technique used for non-military applications was the US government's 56-bit Data Encryption Standard (DES). Indeed, many financial institutions still use 56DES even today.

However, last January the privacy group, the Electronic Frontier Foundation decoded a 56-bit DES message in less than 22 hours. This is not a problem, for the time being, as the encryption industry has moved beyond 56-bit DES and is providing 128-bit encryption that is still impossible to break.

But for Los Alamos National Labs and IBM the issue is not what encryption techniques are secure today, but how secure they will be when the next generations of computers arrive tomorrow.

Surely today's messages will be useless in 10 years. Not so, according to Dr Hughes.

For example, satellite operators use encryption to send messages from earth to position the satellite. So computer crackers could, for instance, decrypt an old message and gain control of a satellite.

To combat this IBM et al have taken today's encryption techniques and modified them with quantum physics. The system works by taking a standard bit or piece of data and translating it into a quantum bit or qubit. This means transferring a bit into a photon and beaming it over fibre optic (glass) cable.

Unlike standard bits, qubits cannot be copied, read or even observed by a third party without altering their state and thus rendering them useless. Once relayed over a fibre optic line to the recipient computer, they are then translated back into a standard bit and read as normal.

"If there is an eavesdropper, the state is immediately altered, and the sender knows that it's been tampered with, so it's absolutely fool-proof," said Mr Nabil Amer, a research scientist at IBM's Almaden Research Center, in San Jose, California.

However, until recently most computer experts believed that quantum encryption was impossible.

"I still believe it's a long way off," said Mr Dave Del Torto, an encryption consultant with Level 7 Digital Labs in San Francisco. "I know it works in theory but the equipment requirements are so far beyond what we have available now that it's still science fiction." IBM's Mr Amer refutes this claim and is charged with making this science fiction a reality.

"We have a working version in our labs right now," said Mr Amer. "What we are trying to do now is to take this experiment and make it a product."

In short, Mr Amer wants to standardise components that will work with standard computer systems.

"I believe that we will have a working product by the year 2002," said Mr Amer. "But it will only be suitable for some very specific applications." The limitations of the new system may dictate the "specific applications".

For instance, at present IBM can only send a message over a 20-kilometre fibre optic link.

Therefore, according to Mr Amer, it is likely that IBM will try to sell this system to banks and electronic commerce institutions to transmit their most sensitive data.

Likewise, the Department of Energy's Los Alamos National Labs will develop very secure encryption systems for the US military.

"I have no doubt that quantum encryption will become a reality in the very near future," concluded Mr Amer.

Niall McKay can be reached at irish-times@niall.org