A new method of quantum cryptography denies espionage attempts

The Quantum Key Distribution, or QKD, used regularly in quantum cryptography is based in Heisenberg’s uncertainty principle, which states how a system is disturbed by actions as simple as being measured. If a spy acts in these systems he or she can read the signal, leaving a print that allows legitimate users to counterattack and make the system safer.

Tokyo University researchers have developed a protocol or a new QKD that works with a different principle, according to Nature magazine. “Instead of detecting espionage attempts, it prevents them; in such a way that the spy can’t read much even if he’s determined to do so” explains Masato Koashi to Sinc.

The scientist proposes an example: “The conventional method is like having an unreliable factory, where it’s products have to be tested strictly so they pass quality control. The new method is like having a reliable factory that ensures good products.”

The new protocol doesn’t require signal disturbance monitoring or measuring its influence in the system. The algorithms and equations that back it up simplify procedures and prevent spies from getting enough information to decode the message,. In situations where channel noise increases, or when communication times are shortened, it also acts better than traditional protocols.

“I’m excited with the new results -says Koashi- because our discovery is a completely different way of hiding information that had gone unnoticed by researchers for 30 years, ever since they realized that quantum mechanics can be used like this in 1984.”

According to its authors, another amazing fact is that the new idea can be implemented in a conventional interferometer with a common laser. The proposed schematics of quantum mechanics consists in sending light impulses that divide in two. One of them gets in a self-induced delayed state and results are measured by photon detectors.

About the perspectives to apply the protocol in the market, the pieces of the possible devices are already available. “The only unknown factor is the variable delay, that can change in a hundred different ways, meaning it can be difficult to set up, but technologically there are no big obstacles” says Koashi.

Anyhow, the researcher recognizes that the potential clients tend to be satisfied with the current cryptographic security levels and are usually against investing more to get better security than the one given by QKD, “even if the new one is more flexible and can be adapted to more situations.”

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