Unformatted text preview: algorithm immune to differential cryptanalysis; they defined the concept of a Markov cipher and showed that resistance to differential cryptanalysis can be modeled and quantified [931, 925]. (Figure 13.10 shows the original PES algorithm to be contrasted with the IDEA algorithm of Figure 13.9 which was strengthened against differential cryptanalysis. It’s amazing how a few subtle changes can make such a big difference.) In [925], Lai argued (he gave evidence, not a proof) that IDEA is immune to differential cryptanalysis after only 4 of its 8 rounds. According to Biham, his relatedkey cryptanalytic attack doesn’t work against IDEA, either [160]. Willi Meier examined the three algebraic operations of IDEA, and pointed out that while they are incompatible, there are instances where they can be simplified in such a way as to facilitate cryptanalysis some percentage of the time [1050]. His attack is more efficient than bruteforce for 2round IDEA (242 operations), but less efficient for 3round IDEA or higher. Normal IDEA, with 8 rounds, is safe. Joan Daemen discovered a class of weak keys for IDEA [406, 409]. These are not weak keys in the sense of the DES weak keys; that is, the encryption function is selfinverse. They are weak in the sense that if they are used, an attacker can easily identify them in a chosenplaintext attack. For example, a weak key is (in hex): 0000, 0000, 0x 00, 0000, 0000, 000x,xxxx,x000 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 © 19962000 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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