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Unformatted text preview: than DES is also less secure (see Table 12.15). A variant of this scheme recently appeared . It is probably no more secure than the original GDES. In general, any large block DES variant that is faster than DES is probably also less secure than DES. DES with Alternate S-Boxes
Other DES modifications centered around the S-boxes. Some designs made the order of the S-boxes variable. Other designers varied the contents of the S-boxes themselves. Biham and Shamir showed [170,172] that the design of the S-boxes, and even the order of the S-boxes themselves, were optimized against differential cryptanalysis: The replacement of the order of the eight DES S-boxes (without changing their value) also makes DES much weaker: DES with 16 rounds of a particular replaced order is breakable in about 238 steps.... DES with random S-boxes is shown to be very easy to break. Even a minimal change of one entry of one of the DES S-boxes can make DES easier to break. The DES S-boxes were not optimized against linear cryptanalysis. There are better S-boxes than the ones that come with DES, but blindly choosing new S-boxes isn’t a good idea. Figure 12.11 GDES. Table 12.15 [167,169] lists some modifications to DES and the number of chosen plaintexts required for differential cryptanalysis. One change not listed, combining the left and right halves using addition mod 24 instead of XOR, is 217 times harder to break than DES . 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)
Brief Full Advanced Search Search Tips (Publisher: John Wiley & Sons, Inc.) Author(s): Bruce Schneier ISBN: 04711...
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