Horace Heffner wrote:
UPDATE - FEBRUARY 16, 2006 An arbitrarily close approximation to an hysteresis free circuit (a circuit producing bits with information entropy approaching 1) can be obtained by XORing the outputs from multiple independent circuits having hysteresis. The XORing can be achieved using simple clocked digital logic. Suppose a circuit is being used that is very fast, but exhibits a hysteresis of about 1 percent. That is to say the probability of a 1 is 0.495 percent, and the probability of a 0 is 0.505 percent. By XORing the output of the two independent circuits, the probability of a 0 drops to 0.495^2 + 0.505^2 = .5005. By XORing the output of four independent circuits, the probability of a 0 drops to 0.4995^2 + 0.5005^2 = .5000005. By XORing the output of eight independent circuits, the probability of a 0 drops to 0.4999995^2 + 0.5000005^2 = .5000000000005. The hysteresis is removed to less than 1 part in 10^12.
That is really cool. Is it original? If so it's surely worth a patent!
This method has the advantage over the Von Neumann whitening method (see: http://en.wikipedia.org/wiki/One_time_pad
Are high-tech one-time-pads of any use? It seems like you need to securely send a key the same length as the message to use it. But if you can do that you can securely send the message itself (it's the same length) so what did you need to encrypt it for?
The original physical one-time-pads used a centrally generated key (printed on the pad) which was carried with the spy to whatever destination. The spy knew whether he'd been caught (obviously) and knew whether he still had the pad with him (obviously) and so could know whether the pad's integrity had been compromised. Thus, in effect, the "channel" from headquarters to the field office was known to be "secure". So, since a copy of the pad was kept back at HQ, he could then send the encrypted message, _without_ the accompanying key, in perfect security, the only hazard being that he had to destroy the clear-text original _and_ his copy of the key in some secure fashion (cigarette lighter and hotel ashtray, for instance).
When you move into the electronic world, though, you're presumably talking about generating the key on the spot, at the point where the encryption takes place. But that's useless! You only need to encrypt the message if the channel isn't secure, but in that case you can't send the key! Again, it seems like the _only_ way a one-time-pad can be useful is in the unusual case where there is a secure _one_ _way_ channel, and you need to transfer information the _other_ _way_. In that unique case the key can be originated at one end and a copy of the key sent securely, and the encrypted data can then be returned insecurely.
