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Unformatted text preview: ndemning DES for having weak keys, consider that this list of 64 keys is minuscule compared to the total set of 72,057,594,037,927,936 possible keys. If you select a random key, the odds of picking one of these keys is negligible. If you are truly paranoid, you could always check for weak keys during key generation. Some people don’t think it’s worth the bother. Others say that it’s so easy to check, there’s no reason not to. There is further analysis on weak and semiweak keys in , and additional key patterns have been investigated for weaknesses. None have been found. Complement Keys
Take the bit-wise complement of a key; that is, replace all the 0s with 1s and the 1s with 0s. Now, if the original key encrypts a block of plaintext, then the complement of the key will encrypt the complement of the plaintext block into the complement of the ciphertext block. If x’ is the complement of x, then the identity is as follows: EK(P) = C EK’(P’) = C’ This isn’t anything mysterious. The subkeys are XORed with the right half after the expansion permutation in every round. This complementation property is a direct result of that fact. Table 12.12 DES Semiweak Key Pairs 01FE 01FE 01FE 01FE and FE01 FE01 FE01 FE01 1FE0 1FE0 0EF1 0EF1 and E01F E01F F10E F10E 01E0 01E0 01F1 01F1 and E001 E001 F101 F101 1FFE 1FFE 0EFE 0EFE and FE1F FE1F FE0E FE0E 011F 011F 010E 010E and 1F01 1F01 0E01 0E01 E0FE E0FE F1FE F1FE and FEE0 FEE0 FEF1 FEF1 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)
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This note was uploaded on 10/18/2010 for the course MATH CS 301 taught by Professor Aliulger during the Fall '10 term at Koç University.
- Fall '10