crypt function mode

[Martin]

On Mon, 2009-04-20 at 12:00 -0400, pam-list-request at redhat.com wrote:
<snip>
> Hi Martin, when you say the following:
> "These are for symmetric encryption, the crypt function uses  them as
> a one way hash (that why the later versions use MD5)."
> 
> Does the crypt function use any of the block cipher mode with little
> modifications. Please clarify.
CBC, EBC, etc. are for encrypting multiple blocks while avoiding block
level frequency analysis, insertion attacks, etc.  crypt does not use
DES for encryption, it uses it as a form of hash, thus chain modes are
simply not applicable.

If you want to understand how it works, I *strong* suggest you read the
code, this will give a far clearer explanation than I will manage.  Note
that the MD5 based system, although it solves the same problem, does so
in a very different manner.

Cheers,
 - Martin