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

In practice a 256 entry table can be precomputed and

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Unformatted text preview: Info | Home Use of this site is subject to certain Terms & Conditions, Copyright © 1996-2000 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 statement. To access the contents, click the chapter and section titles. Applied Cryptography, Second Edition: Protocols, Algorthms, and Source Code in C (cloth) Go! Keyword Brief Full Advanced Search Search Tips (Publisher: John Wiley & Sons, Inc.) Author(s): Bruce Schneier ISBN: 0471128457 Publication Date: 01/01/96 Search this book: Go! Previous Table of Contents Next ----------- 16.8 Rambutan Rambutan is a British algorithm, designed by the Communications Electronics Security Group (one of the aliases used by GCHQ). It is only sold as a hardware module and is approved for the protection of classified material up to “Confidential.” The algorithm itself is secret, and the chip is not generally commercially available. Rambutan has a 112-bit key (plus parity bits) and can operate in three modes: ECB, CBC, and 8-bit CFB. This strongly indicates that it is a block algorithm, but rumors point elsewhere. Supposedly, it is a LFSR stream cipher. It has five shift registers, each one of a different length around 80 bits. The feedback polynomials are fairly sparse, with only about 10 taps each. Each shift register provides four inputs to a very large and complex nonlinear function which eventually spits out a single bit. Why call it Rambutan? Perhaps, like the fruit, it’s spiny and forbidding on the outside but soft and yielding inside. On the other hand, maybe that’s not the reason. 16.9 Additive Generators Additive generators (sometimes called lagged Fibonacci generators) are extremely efficient because they produce random words instead of random bits [863]. They are not secure on their own, but can be used as building blocks for secure generators. The initial state of the generator is an array...
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