If you’ve got communications that absolutely cannot be intercepted—whether you’re a NSA whistleblower, the president of Mexico, or Coca-Cola—quantum cryptography is the way to go.
It harnesses the bizarro-world properties of quantum physics to ensure that information sent from point A to point B isn’t intercepted. The laws of physics dictate that nobody—not even the NSA—can measure a quantum system without disrupting it.
The problem, as Edward Snowden could probably tell you, is that quantum cryptography is still in its infancy. It only works over relatively short distances, and the required gear—including lasers and a dedicated fiber optic network—is prohibitively expensive, limiting its use to a handful of research labs, corporations and governments.
A new research paper from scientists at Toshiba brings quantum cryptography a baby-step closer to the masses. The paper, published today in Nature, explains how to expand a point-to-point quantum network with only two users into a “quantum access network” with up to 64 users.
“This kind of communication cannot be defeated by future advances in computing power, nor new mathematical algorithms, nor fancy new engineering,” said co-author Andrew Shields, head of the Quantum Information Group of Toshiba Research Europe. “As long as the laws of physics hold true, it will ensure that your communications are fully secured.”
A quantum network uses specially polarized photons to encode an encryption key—a very long series of numbers and letters that can unlock a digital file. The photons are then sent down a fiber optic cable until they reach their destination, a photon detector, which counts them, and delivers the key to the intended recipient. If the photons are interfered with, the individual packets of information are forever altered and the recipient can see the telltale signs of tampering.
The Toshiba team focused its efforts on improving the photon detector, and created a system that counts up to 1 billion photons per second, which makes it feasible to add more people to the network. “Our breakthrough is we’ve developed an architecture that is point-to-multipoint. This greatly increase the number of potential users in the network, and reduces costs,” Shields said.
Current quantum cryptography systems from companies like ID Quantique start at around $50,000, and only connect two parties at a time. “If up to 64 people can share a single photon detector than you can spread out those costs,” Shields said.
The next step toward mainstreaming quantum crypto is increasing the distance that photons can travel before they degrade—currently the record is 200 km (124 miles) using a dedicated fiber optic cable. But researchers are working on ways to transmit quantum bits on so-called “noisy” fiber that carries other information, which means that the day may not be far away when your Gmail may have a quantum key.
Until then, it’s probably safer to assume that Big Brother is listening.