http://www.technologyreview.com/view/428202/quantum-cryptography-outperformed-by-classical/
The idea is straightforward. Alice wants to send Bob a message via an
ordinary wire. At each end of the wire, there are two different
resistors that correspond to a 0 or 1.
Alice encodes her message by connecting these two resistors to the wire
in the required sequence.
Bob, on the other hand, connects his resistors to the wire at random.
The crucial part of this set up is that the actual current and voltage
through the wire is random, ideally Johnson noise. The essential
features of this noise are determined by the combination of resistors at
each end. This noise is public--anybody can see or measure it.
Now here's the clever bit. Bob knows which resistor he connected to the
wire and so can work out which resistor Alice must have connected.
But Eve, who is listening in to the publicly available noise, does not
know which resistor was connected at each end and cannot work it out
either because the laws of thermodynamics prevent the extraction of this
information from this kind of signal.
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"It’s cheap to maintain Lies and expensive to maintain Trvth."
--KZK's Maxim
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