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

# The cbc method is specified in ansi x99 54 ansi x919

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Unformatted text preview: : 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 ----------- This scheme appeared in a 1989 draft ISO standard [764], but was dropped in a later version [765]. Security problems with this scheme were identified in [1107, 925, 1262, 372]. (Actually, the version in the proceedings was strengthened after the version presented at the conference was attacked.) In some instances the birthday attack is solvable with a complexity of 239, not 264, through brute force. Do not use this scheme. LOKI Double-Block This algorithm is a modification of Quisquater-Girault, specifically designed to work with LOKI [273]. All parameters are as in Quisquater-Girault. G0 = IG, where IG is a random initial value H0 = IH, where IH is another random initial value Wi = ELi • Gi- 1 (Gi- 1 • Ri) • Ri • Hi- 1 Gi = ERi• Hi- 1(Wi • Li) • Gi- 1 • Hi- 1 • Li Hi = Wi • Gi- 1 Again, in some instances the birthday attack is trivially solvable [925, 926, 1262, 372, 736]. Do not use this scheme. Parallel Davies-Meyer This is yet another attempt at an algorithm with a hash rate of 1 that produces a hash twice the block length [736]. G0 = IG, where IG is a random initial value H0 = IH, where IH is another random initial value Gi = ELi• Ri(Gi- 1 • Li) • Li • Hi- 1 Hi = ELi(Hi - 1 • Ri) • Ri • Hi- 1 Unfortunately, this scheme isn’t secure either [928, 861]. As it turns out, a double-length hash function with a hash rate of 1 cannot be more secure than Davies-Meyer [861]. Tandem and Abreast Davies-Meyer Another way around the inherent limitations of a block cipher with a 64-bit key uses an algorithm, like IDEA (see Section 13.9), with a 64-bit block and a 128-bit key. These two schemes produce a 128-bit hash value and have a hash rate of ½ [930, 925]. Figure 18.11 Tandem Davies-Meyer. In this first scheme...
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