Bugtraq mailing list archives

Re: Not so much a bug as a warning of new brute force attack


From: mouse () Collatz McRCIM McGill EDU (der Mouse)
Date: Sun, 9 Jun 1996 14:03:20 -0400


I would suspect that your average [black-hat] wouldn't know what to
do if he found "$1$rEU5lGMq$x5g.f98lqkUfQ8rn89foQl" in the encrypted
password field.
Yeah, but if it becomes popular, there's not much stopping one of
them with a clue from adding an MD5/rsalib call right after the
crypt() in crack, et al.

Except that once you drop compatability with the past, you can do
things like run the number of rounds up high enough that, once again, a
single crypt() call takes a significant fraction of a cpu-second...at
which point dictionary cracking becomes infeasible.  (Back when
DES-based crypt() was designed, a crypt call _did_ take a significant
fraction of a cpu-second.  It's just 20 years (25? 15? no matter) later
now, and cpus are faster.

I don't know what code FreeBSD is using, but I don't see a round count
in the above hashed password.  My NetBSD libcrypt has not only a format
value in a hashed password, but also a round count.  I haven't yet
tuned the default, but you can certainly run it up until it takes .1
cpu-seconds on a P120 to do a single crypt(), at which point even if
they _do_ have a clue and _do_ modify crack, it's hopeless for another
N years...and you can always just goose the round count again when cpu
speeds catch up.

                                        der Mouse

                            mouse () collatz mcrcim mcgill edu



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