Unformatted text preview: eblock, twokey triple encryption [859]. However, I advise against this sort of thing. It isn’t faster than conventional triple encryption: six encryptions are still required to encrypt two blocks of data. We know the characteristics of triple encryption; constructions like this often have hidden problems. 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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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:
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 15.4 Other Multiple Encryption Schemes
The problem with twokey triple encryption is that it only doubles the size of the keyspace, but it requires three encryptions per block of plaintext. Wouldn’t it be nice to find some clever way of combining two encryptions that would double the size of the keyspace? Double OFB/Counter
This method uses a block algorithm to generate two keystreams, which are then used to encrypt the plaintext. Si = EK1(Si  1 • I1); I1 = I1 + 1 Ti = EK2(Ti  1 • I2); I2 = I2 + 1 Ci = Pi • Si • Ti Figure 15.3 Doubling the block length. Si and Ti are internal variables, and I1 and I2 are counters. Two copies of the block algorithm run in a kind of hybrid OFB/counter mode, and the plaintext, Si, and Ti are XORed together. The two keys, K1 and K2, are independent. I know of no cryptanalysis of this variant. ECB + OFB This method was designed for encrypting multiple messages of a fixed length, for example, disk blocks [186,188]. Use two keys: K1 and K2. First, use the algorithm and K1 to generate a mask of the required block length. This...
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