Imagine, if you will, a means of delivering encryption keys that is so secure that it's impossible to break because doing so would violate the laws of physics. In other words, the delivery method is so secure, it's protected by the very fabric of the universe.
If that doesn't get your attention, think about this: What Dr. Hughes is working with is a way to encode information on individual photons. He then sends these encoded photons to a receiver that can measure their characteristics and determine from those characteristics the data that the encoding represents. That's right. He's imprinting information on individual subatomic particles.
What makes this so secure is that the information can be encoded in several ways. If someone were to intercept these photons, only one of the possible encoding methods could be seen. If that method didn't contain the needed information, the eavesdropper couldn't then look at the information that was encoded differently. So why couldn't a hacker occasionally determine the encoding method by trial and error?
To do so would be pointless because hackers could never be sure they were seeing the real data, and it would violate the Heisenberg Uncertainty Principle of quantum mechanics if the hacker tried to look at both types of polarization on the same particle. Add to these complications that the mere act of observing the photons in their path changes them and that the change is immediately detectable by the recipient.
Photon polarisation 101
Here's how all of this works: Dr. Hughes, who works in the Physics Division at the Los Alamos National Laboratory, creates photons using a very attenuated laser. He's able to choose the polarisation of each photon so that, for example, a vertical polarisation represents a 0 and horizontal polarisation a 1. Or, you can use opposite diagonal polarisations. The order of the polarisation is varied randomly, but the sender has already sent the sequence to the receiver. That way, the receiver doesn't have to look at a bunch of other photons in search of the information; it just looks for the information coming from the transmitter.
The beauty of the method is that even if some hackers knew the order as well, they couldn't gather the information without being detected. Why? Again, Heisenberg: You cannot observe a subatomic particle without changing it. When particles that have been observed arrive at the receiver, their bit error rate is very high, alerting the receiver that the data stream is being observed. As a result, the encoding sequence can be changed immediately, regaining the security of the transmission.
Nice theory, right? But using polarised photons for encryption is more than just a theory. In fact, it's already working in at least two test installations: one is run by BBN Networks and Harvard University, the other by the Army and Navy Research Laboratories near Washington, DC. Both installations transmit the photons over optical fiber. But transmitting photons over optical fiber is limited to about 70 km because using repeaters to strengthen the signal would introduce anomalies similar to those of an eavesdropper. Dr. Hughes thinks the delivery method needs to go beyond that.
"A much more compelling application is by transmitting through the atmosphere," Dr. Hughes explains, adding that he's been able to do single-photon communications through the air in daylight with an acceptable bit error rate. No need to lay all that fibre-optic cable anymore. "The trick," he says, "is to find the single photon against the background." It sounds like a feat requiring equipment only NASA could afford--in fact, transmitting encryption keys to satellites is being tested--but Dr. Hughes says he's mastered "free-space quantum cryptography" using commercial off-the-shelf components.
Even better, you can buy this now. A Swiss company named id Quantique is already selling a device that performs over fiber networks what it calls quantum key distribution. While the wireless optical version Dr. Hughes is testing isn't available now, he says that at least two companies are working on commercial versions. Once these products are available, you can be confident that your communications are secure. Unless someone starts messing around with the universe, anyway.
Will the laws of quantum physics end the theft of transmitted data once and for all? TalkBack below, or e-mail us your thoughts.
Doesn't the poliarization pattern (PP) have to be exchanged securily before the data is transmitted? Why not just exchange the data then? If the PP is a one time pad, it must be at least as long as the data in the first place. The main advantage of this system seems to be that the receiver knows that the message has been comprimised.