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

She also broke quadratic generators xn axn 12 bxn 1

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Unformatted text preview: e 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 ----------- 15.5 CDMF Key Shortening This method was designed by IBM for their Commercial Data Masking Facility or CDMF (see Section 24.8) to shrink a 56-bit DES key to a 40-bit key suitable for export [785]. It assumes that the original DES key includes the parity bits. (1) Zero the parity bits: bits 8, 16, 24, 32, 40, 48, 56, 64. (2) Encrypt the output of step (1) with DES and the key 0xc408b0540ba1e0ae, and XOR the result with the output of step (1). (3) Take the output of step (2) and zero the following bits: 1, 2, 3, 4, 8, 16, 17, 18, 19, 20, 24, 32, 33, 34, 35, 36, 40, 48, 49, 50, 51, 52, 56, 64. (4) Encrypt the output of step (3) with DES and the following key: 0xef2c041ce6382fe6. This key is then used for message encryption. Remember that this method shortens the key length, and thereby weakens the algorithm. 15.6 Whitening Whitening is the name given to the technique of XORing some key material with the input to a block algorithm, and XORing some other key material with the output. This was first done in the DESX variant developed by RSA Data Security, Inc., and then (presumably independently) in Khufu and Khafre. (Rivest named this technique; it’s a nonstandard usage of the word.) The idea is to prevent a cryptanalyst from obtaining a plaintext/ciphertext pair for the underlying algorithm. The technique forces a cryptanalyst to gue...
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