applied cryptography - protocols, algorithms, and source code in c

Memo was a secure electronic mail system for users in

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Unformatted text preview: the eavesdropper can do whatever he wants, even if the eavesdropper has unlimited computing power, even if P = NP. Charles Bennett, Gilles Brassard, Claude Crépeau, and others have expanded on this idea, describing quantum key distribution, quantum coin flipping, quantum bit commitment, quantum oblivious transfer, and quantum secure multiparty computation. Their work is described in [128,129,123,124,125,133,126,394,134,392,396]. The best overview of quantum cryptography can be found in [131]; [1651] is another good nontechnical overview. A complete bibliography of quantum cryptography is [237]. This would still be on the lunatic fringe of cryptography, but Bennett and Brassard actually went and built a working model of the thing [127,121,122]. Now we have experimental quantum cryptography. So sit back, get yourself something to drink, and relax. I’m going to explain what this is all about. According to quantum mechanics, particles don’t actually exist in any single place. They exist in several places at once, with probabilities of being in different places if someone looks. However, it isn’t until a scientist comes along and measures the particle that it “collapses” into a single location. But you can’t measure every aspect (for example, position and velocity) of a particle at the same time. If you measure one of those two quantities, the very act of measuring it destroys any possibility of measuring the other quantity. The quantum world has a fundamental uncertainty and there’s no way to avoid it. That uncertainty can be used to generate a secret key. As they travel, photons vibrate in some direction; up and down, left to right, or more likely at some angle. Normal sunlight is unpolarized; the photons vibrate every which way. When a large group of photons vibrate in the same direction they are polarized. Polarization filters allow only photons that are polarized in a certain direction through; the rest are blocked. For example, a horizontal polarizati...
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This note was uploaded on 10/18/2010 for the course MATH CS 301 taught by Professor Aliulger during the Fall '10 term at Koç University.

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