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up vote 4 down vote accepted

A couple of reasons:

  1. The BCrypt-based scheme isn't NIST approved.

  2. Hash functions are designed for this kind of usage, whereas Blowfish wasn't.

  3. The added security is BCrypt is based on it being computationally expensive, rather than the type of algorithm. Relying on computationally expensive operations isn't good for long-term security.

See http://en.wikipedia.org/wiki/Crypt_%28Unix%29 for some discussion on this.

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Being computationally expensive is exactly why bcrypt is used for this application. – pdo Apr 10 '11 at 12:11
@rob 4. bcrypt adds a dependency that isn't otherwise there, where sha1 and sha2 are part of glibc – xenoterracide Apr 10 '11 at 12:39
What I said in point 3. – Rob Apr 10 '11 at 12:40
Sorry, I'll be more clear. Being computationally expensive, plus having a configurable number of rounds, is exactly why this is a good scheme for long-term security. It allows the cost of checking the hash to increase as hardware gets faster. The original paper describing bcrypt was actually titled "A Future-Adaptable Password Scheme" (usenix.org/events/usenix99/provos/provos_html) – pdo Apr 10 '11 at 13:56
@pdo I don't consider the ability to increase the number of rounds to negate point 3. It may be that additional rounds cancel each other out in some way w.r.t. future cryptoanalytic attacks on the underlying algorithm. – Rob Apr 10 '11 at 15:50

OpenSUSE 11.4 (at least) does use Bcrypt by default.

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Ulrich Drepper, the glibc maintainer, rejected bcrypt support since isn't approved by NIST. See details the article bcrypt support for passwords in /etc/shadow

And his article on homepage Unix crypt with SHA-256/512

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