Quantum cryptography could finally hit the mainstream thanks to a deal that will allow customers to adopt the technology without having to install dedicated optical fibers.

Quantum cryptography--a means of keeping secrets safe by using light particles to help scramble data--has been commercially available for several years. But the technology has only been practical for governmental or large private-sector organizations that can afford to have their own point-to-point optical fiber that the technology requires. But under the new deal, struck between Siemens IT Solutions and Services in the Netherlands and Geneva, Switzerland-based id Quantique, any organizations or individuals wanting state-of-the-art data security will be able to buy the complete package of quantum cryptography and cable.

For the commercial development of quantum cryptography it's a significant step, says Seth Lloyd, an expert in the subject and a professor at MIT. "It makes it a lot more commercially viable. The fiber is by far the most expensive part," he says.

Quantum cryptography is a method that seeks to solve the problem of how to securely send cryptographic keys between two parties by encoding them within light particles, or photons. It allows the parties to share a random--and so almost unbreakable--key without fear of third-party interception. If anyone does try to eavesdrop on the key exchange, the mere act of observing the photons changes them, making the attack detectable.

But for this quantum key distribution (QKD) to work, the same photons transmitted by one party have to be received by the other. This means that unlike most optical fiber data signals, which are periodically amplified by repeaters to boost the signal, quantum keys can only be sent through dedicated, unamplified, point-to-point fibers.

Telecom companies have spent the last few years installing precisely this kind of fiber, but for entirely different reasons, says Lloyd. Known as dark fiber, this is essentially extra capacity that has been laid in bulk to accommodate future growth.

Some companies lease this dark fiber for their own secure data connections, but for the most part it's just laying there waiting for deployment, says Andrew Shields, head of Toshiba Research Europe's Quantum Information Group in Cambridge, U.K. "For quantum key distribution, this is a godsend. There is all this dark fiber in the ground right now that's not being used."

In the new deal, Siemens SIS will offer id Quantique's QKD system over Siemens' existing dark fiber. "It's important from a commercial point of view that companies like Siemens, a global player, are showing an interest in this technology," says Grégoire Ribordy, co-founder and CEO of id Quantique. "There's potential to really accelerate commercial development."

Initially it will only be made available to Dutch customers, says Feike van der Werf, sales director of Siemens SIS, but in time may be deployed more widely. "I see this as the first step in the switch to quantum-based security," says Charlotte Rugers, a security consultant with Siemens SIS.

In essence, this deal means that for the first time QKD will be commercialized and marketed like standard IT services, says Ribordy. Dark fiber has become so prevalent that in some countries you have fiber direct to your home, he says. At the moment it is still not widely used, mainly by organizations that really care about security. But in theory this new deal means that even individuals could adopt the technology, "if you were really paranoid," he says.

This is an important step that should help bring QKD into the mainstream, says Shields. Previously customers were forced to source their own dark fiber, either through laying it themselves or getting a telecom to provide it, but this new deal allows them to buy the complete, scalable package. Although some bigger companies may have their own dark fiber, for smaller companies it would make it easier to adopt the technology, he says. "There are people out there using it but mostly it's to assess the capability, rather than using it to hide their secrets."

It will still be expensive. Besides the $82,000 price tag for a pair of id Quantique's QKD boxes, the cost of dark fiber remains high, because the customer will have to bear the cost of at least two fibers--one for the QKD and the other with which to send the encrypted data once keys have been exchanged. Normally, the cost of each fiber is offset by having dozens of customers share it, says Shields. But QKD customers will be unlikely to want to share their cables. "I think in the longer term we will need to see QKD integrated with normal telecom fibers." But for now this isn't possible, he says. Quantum signals are very weak and classical data signals are very strong, so there is a danger they will be drowned out. Once this problem has been solved, QKD should become even more attractive, he says.

Copyright Technology Review 2009.