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Re: weird crypt-sha* in DragonFly BSD
From: Solar Designer <solar () openwall com>
Date: Mon, 2 Jan 2012 05:11:38 +0400

Matt - as far as I can see, nothing has been done on this yet.
DragonFly still uses by far the weakest password hashing of all *BSDs
(and even of all non-ancient Unix-like systems) by default.  I suggest
that you revert to MD5-crypt ASAP - should be a trivial change for you
to make.  Then change the default to bcrypt or something else
(reasonable) in the future (when you have time).  Thanks!

On Tue, Nov 15, 2011 at 06:35:02AM +0400, Solar Designer wrote:
Hi,

Matthew - when I read that DragonFly moved to using SHA-256 for
passwords by default, I thought this was referring to the SHA-256 based
flavor of Ulrich Drepper's SHA-crypt.  This would not be the best choice
to make, in my opinion, but it would not be that bad.  However, I just
found this:

http://gitweb.dragonflybsd.org/dragonfly.git/tree/HEAD:/lib/libcrypt

Are these crypt-sha256.c and/or crypt-sha512.c files actually in use?
I hope not...  They do not include any password stretching, resulting in
password hashes that are much quicker to crack than MD5-crypt's.

There's also minor weirdness in the code - such as two local pointer
variables being declared static seemingly for no reason, and only
"final" but not "ctx" being zeroized in the end.  But even this lack of
proper cleanup is very minor compared to the lack of stretching.

Oh, also the "$3$" prefix was apparently previously used for NTLM:

http://en.wikipedia.org/wiki/Crypt_(Unix)#NT_Hash_Scheme

"FreeBSD used the $3$ prefix for this."

http://search.cpan.org/~zefram/Authen-Passphrase/lib/Authen/Passphrase/NTHash.pm

"... crypt string must consist of "$3$$" (note the extra "$") followed
by the hash in lowercase hexadecimal."

BTW, I looked at DragonFly's code while analyzing a more subtle issue
with Ulrich's SHA-crypt:

http://www.openwall.com/lists/oss-security/2011/11/15/1

I thought that maybe you reimplemented it in a better fashion avoiding
that issue, but I found this... %-)

Alexander


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