Openssh use enumeration

Selphie Keller selphie.keller at
Thu Jul 21 13:02:57 AEST 2016

I wonder if could be useful to set the fall back account to something user
defined to avoid suggesting people add passwords to root, though I do like
root since the account is always there, but I myself would do that invalid
pass before actually adding a real pass to root, however I think it would
be nice if there was a sshd_config option for fallback_timing_account to
let the user specify something other then root like some generic user they
already have that doesn't involve root. Or have ssh create an dummy account
on the system that has only a invalid password. The fall back to DES seems
ok, but not sure it would fully resolve the issue, since timing for DES and
sha family would be different, but does fix the instant fail for crypt not
understanding blowfish. The random delay idea is pretty good it would make
timing analysis difficult. I wonder if DES + random delay in event root has
no password could be an option.

On 20 July 2016 at 20:48, Darren Tucker <dtucker at> wrote:

> On Thu, Jul 21, 2016 at 12:31 PM, Selphie Keller
> <selphie.keller at> wrote:
> > Ahh i see, just got up to speed on the issue, so seems like the issue is
> > related to blowfish being faster then sha family hashing for longer
> length
> > passwords,
> or the system's crypt() not understanding $2a$ -style salts, which
> most glibcs don't.  On those, crypt fails immediately due to invalid
> salt.
> > so there is a time lag difference between the blowfish internal
> > hash and the sha family hash, though this could be tricky to fix since
> some
> > systems may still use blowfish based hashing and changing the internal
> hash
> The best I could come up with (which is what I implemented[1]) was to
> look the crypt method used for root's password and use that, falling
> back to DES if that fails.  That scheme won't help if you don't set a
> root password (or set it to *LK* or similar), but short of surveying
> all accounts on the system I'm not sure how to do much better.
> [1]
> --
> Darren Tucker (dtucker at
> GPG key 11EAA6FA / A86E 3E07 5B19 5880 E860  37F4 9357 ECEF 11EA A6FA (new)
>     Good judgement comes with experience. Unfortunately, the experience
> usually comes from bad judgement.

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