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According to what I've read it doesn't, in practice, make it any easier or faster to reverse (ie. crack) password hashes such as are used in Linux's /etc/shadow. Still it'd be good to see distros getting away from it as a default ASAP and moving to something like SHA-256.
Its not impossible - it only takes a few days or hours with a modern computer to reverse an MD5 hash, and that was regardless of the recent collision discoveries. You'd hope with SHA-256 or something like that it'd be at least impractical to reverse it - ie. it'd take years or centuries or more.
All this does is generate a string that will generate the same hash as another string, at least that's my understanding.
Yeah that's the impression I got as well. It's a real danger because it means that you can generate, for example, a trojaned ISO file that has the same MD5 sum as the real one.
(the slashdot post has very misleading information)
What the algorithm does is not reverse a hash, not even (still) finding M2 such that H(M1) = X = H(M2), but finding both M1 and M2, the so-called birthday attack. A hash is theoretically secure if the birthday attack is approached by brute-force, but now there's an algorithm to do so.
I still don't know how much it affects shadow hashes. Salts only protects us from rainbow tables (that is, a collection of hashes of known passwords). Fortunately, recent distros have crypt-blowfish. You may configure it with /etc/login.conf. Just add / change the line to: ":passwd_format=blf:\"
You may configure it with /etc/login.conf. Just add / change the line to: "asswd_format=blf:\"
What distro is that on? I've just had a look on both Mandriva2006 and Centos4 and couldn't see anything like that. I think the blowfish stuff needs to be setup and some packages have it built in for it to work. Suse offers the option of blowfish passwords doesn't it?