A quantum leap in codes for secure transmissions

By Jennifer L. Schenker

Published: WEDNESDAY, JANUARY 28, 2004

Scientists at companies in Europe, Asia and the United States say they are close to a commercial version of what they see as an uncrackable way of transporting data.

Among the first customers are expected to be banks and intelligence agencies, as well as governments that want to introduce secure digital services like electronic voting.

The technology, called quantum cryptography, is a radical departure from the way data is secured today.

Throughout history, important messages sent by governments, armies and businesses have relied on codes that are encrypted at one end and decrypted by the recipient. But to make this happen, information about the code has to be shared by at least two people via courier, or, as is more often the case in modern times, via a communications network. And that relay makes the codes susceptible to interception.

Physics promises to change that by using photons that are tamper-proof.

Most secure digital data communications today is based on the use of very long prime numbers, called keys. Two keys are involved in each encryption: a private key, which only the sender has access to, and a public key, available to anyone. The two keys work together, so a message scrambled with a public key can be unscrambled only with the private key. Public key systems require that the sender know the recipient's public key to encrypt a message. So a global registry of public keys is required.

A weakness of this system is that, given a powerful enough computer, it is possible to figure out the private key from the public key. Quantum cryptography allows the secrecy of the key to be guaranteed without the need to make any assumptions about the guile or computing power of a hacker. It also abolishes the need for trusting a registry.

It uses single photons — discrete particles of light — to transfer the numeric keys. The photons are so delicate that if anyone or anything tries to spy on their travels through fiber optic cables, their encoded state will change. The sender and recipient are immediately tipped off to this interference by error messages and so know not to use the key.

Quantum cryptography is one of the first applications of quantum physics, which is expected to replace today's binary system of computing, in which data is represented in series of ones and zeros.

Sometime between 2015 and 2020, scientists say they hope binary bits will be encoded on particles like photons or electrons. These quantum bits would allow computers to perform multiple complex calculations simultaneously.

Quantum computing increases the processing power of computers so substantially that it will be a "greater step than the move from the abacus to the calculating computer," said Charles Ross, a consultant with the London-based Cientifica, who participated in quantum computing trials financed by the European Commission in 1998.

Quantum cryptography is the application of this system that may be the closest to near-term use. That is a good thing, experts say, because they expect hackers to be able to eventually crack even the best security system in place today. The only thing that could stop them is quantum cryptography.

Quantum cryptography has already captured the interest of Visa International, the credit card organization representing some 21,000 banks.

"In our industry, it is important to look some time ahead and consider the technologies that may be needed," said Stuart Brocklehurst, a London-based senior vice president and head of payments development at Visa, which is preparing to test the technology.

"If ever conventional codes become a problem, and we can see there is a potential of this happening in future, quantum computing will give us something ready we can put in," Brocklehurst said. "I certainly see it being widely adopted by the banking community."

MagiQ Technologies, a New York company, and id Quantique, based in Geneva, have both recently started selling quantum cryptography products. After years of research work, larger players like NEC, Toshiba and Hewlett-Packard also say they are getting closer to introducing products.

The cost of such a system could be several hundreds of thousands of dollars per company network, according to John Rarity, a professor at the University of Bristol in Britain. He is part of an $11 million, four-year European Union-financed project called "Secure Communications with Quantum Computing" that will start in March.

But plenty of kinks still have to be worked out. Quantum crypto messages sent over fiber optic cable cannot travel very far, and can only work point-to-point — in other words, with computers directly connected to each other, not those linked by a network.