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New, improved computer security pr NY Times +

This seems to sum it up fairly clearly:

a technique for making infinitesimally short time measurements needed to capture pulses of quantum light hidden in streams of billions of photons transmitted each second in data networks. Scientists used an advanced photodetector to extract weak photons from the torrents of light pulses carried by fiber optic cables, making it possible to safely distribute secret keys necessary to scramble data over distances up to 56 miles.

Such data scrambling systems will most likely be used first for government communications systems for national security. But they will also be valuable for protecting financial data and ultimately all information transmitted over the Internet.

The approach is based on quantum physics, which offers the ability to exchange information in a way that the act of eavesdropping on the communication would be immediately apparent. The achievement requires the ability to reliably measure a remarkably small window of time to capture a pulse of light, in this case lasting just 50 picoseconds — the time it takes light to travel 15 millimeters.
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Or, even better:

“We can pick out the quantum photons from the scattered light using their expected arrival time at the detector,” Dr. Shields said. “The quantum signals hit the detector at precisely known times — every one nanosecond, while the arrival time of the scattered light is random.”

Despite their ability to carry prodigious amounts of data, fiber-optic cables are also highly insecure. An eavesdropper needs only to bend a cable and expose the fiber, Dr. Shields said. It is then possible to capture light that leaks from the cable and convert it into digital ones and zeros.

“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,” he said. “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.”
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Cool.
 
I'm not sure if the person doing the eavesdropping (read the second example) could not intercept the signal completely and then send it on through with the appropriate changes; because of the way the time signature is involved with the exchange (conversation).

Unless it was for something very simple they would not be able to convincingly duplicate the entire exchange for both parties... without a time machine.
 
The quantum world doesn't work like the macro world. Quantum communications systems do something like generate a pair of entangled photons, send one off to the receiver and keep the other. Then, when the photon reaches it's destination, a bit is encoded on the photon that was kept and because the two photons were entangled the receivers sees the bit on their photon. The communication cannot be intercepted and regenerated because the regenerated photon would not then be entangled with the kept photon or if it was, there would not be any information left behind that the interceptor could use.

ETA: see Quantum cryptographyWP
 
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This doesn't seem like great security.

So you can tell if someone has intercepted the information or not. So? They already have what they wanted and if they can use it before you have a chance to change the usefulness said information, then you knowing they listened in isn't that useful. You could always send test signals to test if the line is secure or not, and then not send if it's shown to be compromised, but then there would have to be some security of systems there too so that the interceptor doesn't just send back an 'all clear' signal regardless of what the receiver knows.

I read about this back in college. It's been a few years and it's still not being used.
 
The trick is to send the key using QKD. Then only when you know that the key was not intercepted, you encrypt and transmit the message over a normal channel. In fact, it is rather difficult to send information directly over the quantum channel. What comes out is unpredictable noise. But that is just what you want for a one time pad.
 
tyr_13 said:
So you can tell if someone has intercepted the information or not. So? They already have what they wanted and if they can use it before you have a chance to change the usefulness said information, then you knowing they listened in isn't that useful. You could always send test signals to test if the line is secure or not, and then not send if it's shown to be compromised, but then there would have to be some security of systems there too so that the interceptor doesn't just send back an 'all clear' signal regardless of what the receiver knows.
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The important point is that it's not just one person sending information to another, it requires them both to exchange information. If someone intercepts anything, both parties will know about it. So what you do is try to send an encryption key. If that's done successfully, you're good to go using it to send the actual data you want to send. If not, you just try again with a new key. In theory it would be possible to block communication entirely by ensuring you intercept every single attempted key exchange, but it's never possible to get access to the key without anyone knowing, so you can never get access to the actual encrypted information.

I read about this back in college. It's been a few years and it's still not being used.
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Because it's not ready yet. The whole point of this advance is that previously it was not possible to use this method without having a whole extra set of fibreoptic cables dedicated solely to quantum encryption. Given how difficult it seems to be to get even one fibrepoptic connection to most people, obviously that's not going to happen any time soon. This research shows that it could be possible to use QKD with existing infrastructure, and therefore brings it much closer to widespread commercial use.
 
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