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Unformatted text preview: hey are much better odds than the Government gives on its lotteries, for instance. “Oneinamillion”? “Couldn’t happen again in a thousand years”? It is no longer possible to say such things honestly. Is this an acceptable ongoing risk? Using an algorithm with a 64bit key instead of a 56bit key makes this attack 256 times more difficult. With a 40bit key, the picture is far more bleak. A network of 400 computers, each capable of performing 32,000 encryptions per second, can complete a bruteforce attack against a 40bit key in a single day. (In 1992, the RC2 and RC4 algorithms were approved for export with a 40bit key—see Section 13.8.) A 128bit key makes a bruteforce attack ridiculous even to contemplate. Industry experts estimate that by 1996 there will be 200 million computers in use worldwide. This estimate includes everything from giant Cray mainframes to subnotebooks. If every one of those computers worked together on this bruteforce attack, and each computer performed a million encryptions per second every second, it would still take a million times the age of the universe to recover the key. Neural Networks
Neural nets aren’t terribly useful for cryptanalysis, primarily because of the shape of the solution space. Neural nets work best with problems that have a continuity of solutions, some better than others. This allows a neural net to learn, proposing better and better solutions as it does. Breaking an algorithm provides for very little in the way of learning opportunities: You either recover the key or you don’t. (At least this is true if the algorithm is any good.) Neural nets work well in structured environments where there is something to learn, but not in the highentropy, seemingly random world of cryptography. Previous Table of Contents Next Products  Contact Us  About Us  Privacy  Ad Info  Home Use of this site is subject to certain Terms & Conditions, Copyright © 19962000 EarthWeb Inc. All rights reserved. Reproduction whole or in part in any form or medium without express written permission of EarthWeb is prohibited. Read EarthWeb's privacy st...
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 Fall '10
 ALIULGER
 Cryptography

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