Digital Encryption At The Quantum Level
November 20, 2012

Cheaper Internet Security, Thanks To Quantum Physics

Michael Harper for — Your Universe Online

Toshiba and Cambridge University have been working together to find a cheaper and more efficient way to protect networks from criminal thievery and spying. To find the answer, these two teams looked to quantum physics, landing on a solution which allows high-speed fiber cables to be just as secure as dedicated fiber optics lines. Though this advance will likely first appear in government and military networks, this method could one day make the grid work of fibers and wires which makes up the whole of the Internet a safer place.

The research, conducted by The Cambridge Research Laboratory of Toshiba Research Europe Ltd and the Cambridge University Engineering Department, is set to be published today in the science journal Physical Review X. In it, the teams describe a method for capturing single photons (or particles of light) amongst streams of billions of other photons. Each single photon can be captured in an incredibly short amount of time and can be isolated and captured on its own, leaving the rest of the stream to pass through. This single photon may carry a weak signal, but it´s strong enough to carry all the encryption needed to protect the rest of the traffic. By breaking down the encryption key to a single photon, those monitoring the security of a network will be able to detect an intruder more easily. Any hacker who attempts to break into or eavesdrop on the network runs a larger risk of leaving their footprint behind, inevitably altering the encryption photon in one way or another.

“The laws of quantum physics tell us that if someone tries to measure those single photons, that measurement disturbs their state and it causes errors in the information carried by the single photon,” explained Dr. Andrew Shields, assistant managing director for Toshiba Research Europe and co-author of the paper, speaking to the New York Times.

“By measuring the error rate in the secret key, we can determine whether there has been any eavesdropping in the fiber and in that way directly test the secrecy of each key.”

Until now, keeping a network secure was no easy task. Companies and organizations using public key cryptography have some element of security, though it is still possible to hack these keys and therefore gain access to the network. There are other ways to exchange one-time encrypted keys back and forth between administrator and user, and even some quantum key distribution services similar to the method worked out by Cambridge and Toshiba. These existing methods, however, require the use of a separate, dedicated fiber line to exchange these keys. Separating the network from the encrypted keys as an extra cost and extra difficulty says Dr. Shields.

“The requirement of separate fibers has greatly restricted the applications of quantum cryptography in the past, as unused fibers are not always available for sending the single photons, and even when they are, can be prohibitively expensive. Now we have shown that the single photon and data signals can be sent using different wavelengths on the same fiber,” explained Dr. Shields in a statement.

The Cambridge and Toshiba teams then began combining the single photon encryption key with the main stream of data and set up a photon detector on the receiving end. This detector was set up to capture information in an incredibly small window of time, just 50 picoseconds. This is the same amount of time it takes light to travel 15 millimeters.

“We can pick out the quantum photons from the scattered light using their expected arrival time at the detector,” Dr. Shields said, speaking to the New York Times.

“The quantum signals hit the detector at precisely known times – every one nanosecond, while the arrival time of the scattered light is random.”