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Researchers Say They Have Designed an 'Unhackable' Fiber Network

For the first time, researchers demonstrate how to make quantum key distribution work on a 200Gbit/sec line.
Professor Andrew Lord and Dr Andrew Shields in front of a demo of the technology at BT's Adastral Park labs. The spool in the middle holds 50km of fibre. Image: Nicole Kobie

Researchers are touting "impossible to hack" fibre networks after a trio of tech firms unveiled a superfast working demonstration of quantum key distribution, which uses photons to send encryption keys.

Quantum cryptology is a decades-old idea that photons—particles of lights—can be used to distribute the keys used for protecting sensitive data, such as bank statements or health records. Now it's being used on regular high-bandwidth networks, on a whopping 200Gbit/sec connection over a 100km line, after key problems were cracked by Toshiba Research, BT, and ADVA Optical Networking.


Here's how it works. Encryption keys are generated at one end of the fibre connection, and sent alongside the data on photons. "Photons as quantum particles have this rather delightful characteristic that if [anyone] fiddles with them, you know about it—there's just no way to fiddle with a photon and have people not know that you've fiddled with a photon," said Dr Tim Whitley, head of research and innovation at BT.

And if the photon has been fiddled with and the key is compromised, then it won't be used, meaning the data can't be accessed. "Because we're forming secret keys, we just won't use the keys if we find out that they've been hacked, so there's no chance of losing any information this way," Andrew Shields, assistant managing director at Toshiba Research Europe, told me.

"[Quantum key distribution is] this super guarantee that people just can't compromise your security without you knowing about it."

His colleague, Andrew Lord, head of optical research at BT and visiting professor at the University of Essex, said that essentially means data protected this way is "impossible to hack" while being transmitted.

The technology has been in the works for years: BT filed patents on it back in 1983, and showed a demonstration sending encrypted keys via photons in the mid-90s, but data couldn't be sent at the same time without distorting the keys.

Quantum signals are very weak—less than a photon per bit—compared to ordinary signals, at more than a million photons per bit, the researchers explained. That means they're "easily overwhelmed" by the standard light signals, so would require the expensive installation of "dark fibre"—essentially their own side network not being used to transmit data.


Working alongside BT and ADVA, Toshiba's researchers figured out how to filter the light to pick up the single photon out of the rest of the noise, meaning the quantum keys could be sent on the same fibre strand as other data.

Image: Nicole Kobie

That means this form of quantum key distribution works on existing fibre optic cables, which is handy as rolling out new fibre would cost billions and take decades, Whitley noted. While in the UK BT would need to install new equipment in its street-side cabinets to use quantum encryption, Whitely said that's a common infrastructure update, and the technology could simply be included as part of regular upgrades.

That, along with being able to encrypt data at 200Gbits/sec over 100km lines, shows the technology can actually be used across mainstream networks, rather than just for niche applications. Previous attempts were limited to 40Gbits/sec, but the standard for fibre transmission is likely to be the 100Gbits/sec data format, so the trials show it can work with standard networks.

Whitley expects that within the decade, such protection will be standard, offering data transmissions "where the security is guaranteed by the laws of physics."

"The goal is really profound," Whitley told me. "If you roll forward a decade, my belief is that telecommunications networks around the world will be secured using quantum key distribution, which is this super guarantee that people just can't compromise your security without you knowing about it."

Such protection is important as fibre networks are relatively easy to tap. "If you take a fibre and bend it, some of the light will come out," said Professor Lord. "If you can detect that light, you're close to being able to tap into that system, which is a big issue."

Indeed, it's not only hackers that are an issue: reports suggest government spies may have been tapping broadband networks. I asked BT's Whitley if this breakthrough could stop fibre networks—currently being rolled out across the UK—from being tapped. "Exactly how this stuff rolls out, we don't know—but in theory, yes, that's exactly right," he said.