This is the fix to the Secure Hash Standard, NIST FIPS PUB 180: In Section 7 of FIPS 180 (page 9), the line which reads "b) For t=16 to 79 let Wt = Wt-3 XOR Wt-8 XOR Wt-14 XOR Wt-16." is to be replaced by "b) For t=16 to 79 let Wt = S1(Wt-3 XOR Wt-8 XOR Wt-14 XOR Wt-16)." where S1 is a left circular shift by one bit as defined in Section 3 of FIPS 180 (page 6): S1(X) = (X<<1) OR (X>>31). This is exactly one additional line in assembly language. The very fact that this correction had to made offers some insights into the National Security Agency. I believe that releasing DES to the public was the biggest cryptography mistake that NSA ever made. Consider the state of research in cryptology before DES. It was simplistic. It was haphazard. There was little interest. If any results of value were ever discovered, the NSA could squash them with a secrecy order. No one cared. Then, in the late 1970s, came DES. Suddenly there was a an algorithm to argue about, dissect, study, and learn from. A whole generation of cryptographers learned their craft from DES. Even today, we're still learning from DES. We're learning new techniques of cryptography and cryptanalysis. DES has transformed academic cryptology in ways the NSA never envisioned. The NSA will not make this mistake again. They will not release Skipjack or any other algorithm to the public, because that could galvanize another fifteen years of research in algorithm design and analysis. (Even so, I believe that Skipjack is similar in design to DES; the NSA realizes that Clipper chips will be reverse-engineered eventually.) When it came time to propose an algorithm for the SHS, the NSA chose not to use an algorithm from its own arsenal. Instead it chose to take an algorithm from academia, Ronald Rivest's MD4, and modify it to produce a 160-bit hash. While this approach did not compromise any of NSA's work, it also short circuited NSA's lengthy internal algorithm design and review process. The SHA was announced only two years after MD4. By contrast, NSA claims to have spent five years designing and analyzing their Skipjack algorithm, based on an additional seven years of design. There is no substitute for years of intense cryptanalysis, and the flaw in SHA illustrates that.
From owner-cypherpunks Tue Jun 21 20:47:03 1994