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## Quantum Cryptography Conquers Noise Problem79

ananyo writes "Quantum-encryption systems that encode signals into a series of single photons have so far been unable to piggyback on existing telecommunications lines because they don't stand out from the millions of others in an optical fiber. But now, physicists using a technique for detecting dim light signals have transmitted a quantum key along 90 kilometers of noisy optical fiber. The feat could see quantum cryptography finally enter the mainstream. The researchers developed a detector that picks out photons only if they strike it at a precise instant, calculated on the basis of when the encoded photons were sent. The team's 'self-differentiating' detector activates for 100 picoseconds, every nanosecond. The weak charge triggered by a photon strike in this short interval would not normally stand out, but the detector measures the difference between the signal recorded during one operational cycle and the signal from the preceding cycle — when no matching photon was likely to be detected. This cancels out the background hum. Using this device, the team has transmitted a quantum key along a 90-kilometer fiber, which also carried noisy data at 1 billion bits per second in both directions — a rate typical of a telecommunications fiber."
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## Quantum Cryptography Conquers Noise Problem

• #### Re:20/20 transmission (Score:5, Insightful)

on Tuesday November 20, 2012 @08:14PM (#42049255) Journal
Send a handshake message used to calculate transit time, and then another to specify when the next packet will be sent, or at what intervals. If it fails redo the handshake.
• #### Still completely irrelevant (Score:4, Insightful)

on Wednesday November 21, 2012 @02:24AM (#42051831)

There are numerous problems:
1. You need _optical_ switches, i.e. switched circuits. That approach failed a long time ago. Anybody remember ATM?
2. 90km is nothing. Amplification is impossible, so unless they reach 10'000km, this is completely irrelevant.
3. Nobody needs it. Cryptography does fine. (No, this is at best "quantum modulation", no crypto involved.) If you are paranoid, use OTPs. They are far, far cheaper, far, far more reliable and completely compatible with existing networks.
4. Remember, this is only key exchange, not actual data transmission. As such it is pretty useless, as you still need to rely on cryptography for the message transfer.
5. The security guarantees are far, far weaker than people are made to believe. Just look at the history of successful compromises.
6. Not even the physics may work out. Quantum theory is a _theory_, not established fact.

Another worthless stunt.

• #### Re:Why is it called quantum "cryptography"? (Score:3, Insightful)

on Wednesday November 21, 2012 @02:25AM (#42051845)

Pure marketing BS. It is "quantum modulation", no cryptography involved at all. At it is completely irrelevant anyways. The people doing this have to outright lie to get continued funding.

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