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

authors bruce schneier isbn 0471128457 publication

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Unformatted text preview: being created. The fix to this problem is to hash the Randseed array before storing it, perhaps by just calling genrand(). When the system reboots, you read in the seed file, pass it to churnrand(), then promptly destroy it. Unfortunately, this does not deal with the threat of someone stealing the seed file between reboots and using it to guess future values of the genrand() function. I see no solution to this problem other than to wait until enough external random events have taken place after a reboot before allowing genrand() to produce results. 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 © 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 ----------- Chapter 18 One-Way Hash Functions 18.1 Background A one-way hash function, H(M), operates on an arbitrary-length pre-image message, M. It returns a fixed-length hash value, h. h = H(M), where h is of length m Many functions can take an arbitrary-length input and return an output of fixed length, but one-way hash functions have additional characteristics that make them one-way [1065]: Given M, it is easy to compute h. Given h, it is hard to compute M such that H(M)= h. Given M, it is hard to find another message, M’, such that H(M) = H(M’). If Mallory could do the hard things, he would undermine the security of every protocol that uses the one-way hash function. The whole point of the one-way hash function is to provide a “fingerprint” of M that is unique. If Alice signed M...
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