The most dangerous weapon on the battlefield of the future is information. Just ask Tom Clancy, or any of the hundred knockoffs using his name. But we grew up being told the most dangerous weapon would be lasers, usually hand-portable lasers that could be seen by the naked eye, moved slower than bullets and seemed incapable of killing anyone who wasn't wearing a full face mask. A new advance could combine both, using lasers to beam perfectly secure information around the globe.
We've known of an utterly unbreakable code for a long time . Using a "one-time pad", a pre-arranged codephrase, two parties can beam messages to each other via CNN headlines secure in the knowledge that no-one else in the world can ever crack it. But this one-time pad has to be at least as long as the message and can never be used again, so the cryptographic challenge is to find a way that two people can exchange an absolutely secure key without meeting in trenchcoats in Vienna whispering "The rolling moss gathers two in the bush."
Quantum Key Distribution (QKD) promises to deliver these pads secured by the basic laws of the universe. By encoding the pad in quantum states, the researchers utilize the fact that quantum observations are like five year olds in a china shop: just looking at it can break it, the message's target knows not to use that key, and the eavesdropper has done nothing but alert his targets (and presumably invoked the wrath of James Bond).
These keys can be encoded into laser pulses, a method with a maximum range of about 160 km in the atmosphere. Which is why a bunch of researchers at the University of Padova and the Institute of Quantum Optics and Quantum Information, Vienna, quite reasonably said "So lets just avoid the atmosphere" and bounced the laser off a mirrored satellite. Traveling a thousand five hundred kilometers in all, the photons were only attenuated by eight kilometers of atmosphere - and by altering the angle of reflection the potential range is massively enhanced. Also, by bouncing a damn laser beam off a satellite to deliver top secret information, the team dramatically reaffirmed the fact that Science Is Awesome.
It's important to remember that this is still only perfectly secure in theory. Mortgages area great way to eventually own your home, in theory, and that hasn't exactly been working out. Professor Hoi-Kwong Lo's group in the University of Toronto have demonstrated flaws in current commercial quantum encryption systems, exploiting the points where the human implementation doesn't quite live up to the mathematical ideal. They've also designed secure solutions - at least, until they decide it's time to find more mistakes.
It's still not perfect laser security (ie using lasers to vaporise anyone who tries to break it), but with active teams playing both sides of the game it's improving all the time.
Posted by Luke McKinney.
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