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

authors bruce schneier isbn 0471128457 publication

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Unformatted text preview: ivacy 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 ----------- Patents and Licenses LOKI is not patented. Anyone can implement the algorithm and use it. The source code implementation in this book is copyrighted by the University of New South Wales. Anyone interested in using this implementation (or their other implementation, which is several orders of magnitude faster) in a commercial product should contact Director CITRAD, Department of Computer Science, University College, UNSW, Australian Defense Force Academy, Canberra ACT 2600, Australia; FAX: +61 6 268 8581. 13.7 Khufu and Khafre In 1990 Ralph Merkle proposed two algorithms. The basic design principles behind them are [1071]: 1. DES’s 56-bit key size is too small. Considering the negligible cost of increasing the key size (computer memory is cheap and plentiful), it should be increased. 2. DES’s extensive use of permutations, while suitable for hardware implementations, is very difficult to implement in software. The faster software implementations of DES implement the permutations by table lookup. Table lookup can provide the same “diffusion” characteristics as permutation and can be much more flexible. Table 13.3 P-Box Permutation 32, 24, 16, 8, 31, 23, 15, 7, 30, 22, 14, 6, 29, 21, 13, 5, 28, 20, 12, 4, 27, 19, 11, 3, 26, 18, 10, 2, 25, 17, 9, 1 3. The S-boxes in DES are small, with only 64 4-bit entries per box. Now that memory is larger, S-boxes should grow. Moreover, all eight S-boxes are used simultaneously. While this is suitable for hardware, it seems like an unreasonable restriction in software. A larger S-box size and sequential (rather than parallel) S-box usage should be employed. 4. The initial and final permutations in DES are widely...
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