"The Entropy Key uses P-N semiconductor junctions reverse biassed with a
high enough voltage to bring them near to, but not beyond,
breakdown in order to generate noise. In other words, it has a
pair of devices that are wired up in such a way that as a high
potential is applied across them, where electrons do not
normally flow in this direction and would be blocked, the high
voltage compresses the semiconduction gap sufficiently that the
occasional stray electron will quantum tunnel through the P-N
junction. (This is sometimes referred to as avalanche noise.)
When this happens is unpredictable, and this is what the Entropy Key
measures."
Priced at 36 euros in small quantities.
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When confronted by a difficult problem, solve it by reducing it to the question, "How would the Lone Ranger handle this?"