On Fri, 16 Aug 2002 15:47:54 -0000, you said: > I am thoroughly confused by this avenue of debate. The md5 hashing algorithm > is based on the DES encryption algorithm. This is a reversible symetric I double-checked my copy of Schneier's Applied Cryptography, and unless there's a glaring error that's fixed in the second edition, there seems to be little or no relationship between MD5 and DES. For starters, DES is a 16-round system, and has these mysterious S-boxes and expansion permutations, neither of which are present in MD5. Also, note that unlike the reversible operations in DES, the nonlinear operations used by MD5 lose information (which they would have to, as they are taking the entropy of the entire input datastream and outputting only 128 bits of entropy - that means that N-128 bits of entropy have to be discarded while running the algorithm). At least in my copy of Applied Cryptography, DES is covered in chapter 10, MD5 is covered in 14.5, and the concept of using a symmetric block algorithm as a hash function is covered separately in 14.11 (further pointing out that MD5 isn't a symmetric block system). -- Valdis Kletnieks Computer Systems Senior Engineer Virginia Tech
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