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Security: Quantum Cryptography


Quantum Cryptography

EnlargeIt can keep a secret—really.

by Cade Metz

When you first read about quantum mechanics in a college textbook, it seems ridiculous. Electrons can spin in two different directions at the same time. They quit spinning both ways when you look at them. It sounds a lot like Snuffleupagus, a character who shows up only when no adults are around. The idiosyncrasies of electrons, photons, and other very small particles are so very different from the behaviors of objects you can see and touch as to stretch belief.

But quantum mechanics isn’t fantasy. It’s hard science, and it could soon affect our macroscopic lives. Drawing on 20 years of academic research, two companies have used the principles of quantum mechanics to create the most secure form of computer encryption the world has ever seen.

id Quantique introduced a quantum cryptography system last summer, and MagiQ Technologies will follow suit by the end of this year. These systems use photons to send secret encryption keys, hiding each key behind the most famous tenet of quantum mechanics, the Heisenberg Uncertainty Principle. When you exchange quantum keys with someone, you can be sure that no one could ever hope to figure them out. Any e-mail message, telephone call, or financial transaction encrypted with these keys will be safe.

“If there are things that you want to keep protected for another 10 to 30 years, you need quantum cryptography,” says Burt Kaliski, chief scientist at RSA Security, the world’s leading cryptography company.

The reigning encryption technique is RSA encryption, which lets two people send each other private messages over the Internet using a public key and a private key. Cracking RSA is extremely difficult, but given many years, today’s supercomputers can do it.

RSA keeps improving as machines get faster, but it will be absolutely useless if scientists ever develop a quantum computer. While a silicon transistor is either on or off—holding either a 1 or a 0—an electron in a quantum computer can exhibit two different spins at the same time, holding both values at once. A machine that tapped into this superposition principle would be exponentially faster than any current supercomputer.

How can you protect your data from a quantum computer? You have to fight fire with fire by using encryption based on quantum mechanics.

According to the Heisenberg Uncertainty Principle, if you try to measure the behavior of a quantum particle, you alter it in such a way that your measurement isn’t completely accurate. This means if you send encryption keys using photons, which adhere to the laws of quantum mechanics, no one can steal them.

The example on page 108 steps through the process. Alice sends Bob a series of individual photons, using the polarization of each photon to indicate a binary digit. If Eve tries to read the photons en route, she can’t help but change their polarizations in some cases, leaving telltale signs she was eavesdropping.

As the photons reach Bob and he tries to read them, he ends up changing polarizations as well. But he doesn’t change them all, and with the help of a clever algorithm, he and Alice can confer and ascertain which photons he altered and which he didn’t. They can then determine whether Eve was eavesdropping and, if she wasn’t, build an encryption key that no one could ever hope to deduce.

The only problem is that the photons must travel over a medium that doesn’t disturb their polarizations. You have to send them across a dedicated fiber-optic cable, and with current technology, the line can’t stretch any longer than a few dozen kilometers.

MagiQ Technologies is working on a technique that skirts this limitation, and some say that quantum cryptography systems are already up and running in Washington. “I’m sure that the government is already using quantum cryptography systems for real applications,” says Chris Fuch, a Bell Labs researcher. Still skeptical about quantum mechanics? You shouldn’t be.

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July 16, 2009 - Posted by | Streamin, Tech News | , , , , , , ,

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