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

6 one md5 operation the four rounds 64 steps look

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Unformatted text preview: ar to those in Khafre (see Section 13.7). Some rotations are thrown in, too. Originally Snefru was designed with two passes. Cryptanalysis of Snefru Using differential cryptanalysis, Biham and Shamir demonstrated the insecurity of two-pass Snefru (128-bit hash value) [172]. Their attack finds pairs of messages that hash to the same value within minutes. 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 ----------- On 128-bit Snefru, their attacks work better than brute force for four passes or less. A birthday attack against Snefru takes 264 operations; differential cryptanalysis can find a pair of messages that hash to the same value in 228.5 operations for three-pass Snefru and 244.5 operations for four-pass Snefru. Finding a message that hashes to a given value by brute force requires 2128 operations; differential cryptanalysis takes 256 operations for three-pass Snefru and 288 operations for four-pass Snefru. Although Biham and Shamir didn’t analyze 256-bit hash values, they extended their analysis to 224-bit hash values. Compared to a birthday attack that requires 2112 operations, they can find messages that hash to the same value in 212.5 operations for two-pass Snefru, 233 operations for three-pass Snefru, and 281 operations for four-pass Snefru. Currently, Merkle recommends using Snefru with at least eight passes [1073]. However, with this many passes the algorithm is significantly slower than either MD5 or SHA. 18.3 N- Hash N-Hash is an algorithm invented by researchers at Nippon Telephone and Telegraph, the same people who invented FEAL, in 1990 [1105, 1106]. N-Hash uses 128-bit message blocks, a complicated randomizing function similar to FEAL’s, and produces a 128-bit hash value. The hash of each 128-bit block is a function of the block and the hash of the prev...
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