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

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Unformatted text preview: ity of a one-way hash function is its one-wayness. The output is not dependent on the input in any discernible way. A single bit change in the pre-image changes, on the average, half of the bits in the hash value. Given a hash value, it is computationally unfeasible to find a pre-image that hashes to that value. Think of it as a way of fingerprinting files. If you want to verify that someone has a particular file (that you also have), but you don’t want him to send it to you, then ask him for the hash value. If he sends you the correct hash value, then it is almost certain that he has that file. This is particularly useful in financial transactions, where you don’t want a withdrawal of $100 to turn into a withdrawal of $1000 somewhere in the network. Normally, you would use a one-way hash function without a key, so that anyone can verify the hash. If you want only the recipient to be able to verify the hash, then read the next section. 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 ----------- Message Authentication Codes A message authentication code (MAC), also known as a data authentication code (DAC), is a one-way hash function with the addition of a secret key (see Section 18.14). The hash value is a function of both the pre-image and the key. The theory is exactly the same as hash functions, except only someone with the key c...
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