Date: Tue, 11 Apr 2017 20:58:30 -0400
From: Stephen Frost <sfrost@snowman.net>
To: Bruce Momjian <bruce@momjian.us>
Cc: =?iso-8859-1?Q?=C1lvaro_Hern=E1ndez?= Tortosa <aht@8kdata.com>,
	Andres Freund <andres@anarazel.de>,
	Heikki Linnakangas <hlinnaka@iki.fi>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Some thoughts about SCRAM implementation
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Bruce,

* Bruce Momjian (bruce@momjian.us) wrote:
> On Tue, Apr 11, 2017 at 02:53:24PM +0200, =C1lvaro Hern=E1ndez Tortosa wr=
ote:
> >     Let's put ourselves on the foot of potential users. Why would anyone
> > want to use SCRAM? What for? The hashing mechanism is better, no questi=
on.
> > And bring some added benefits, true. So its "better". But the real gain
> > comes from using channel binding, which avoids impersonation, MITM atta=
cks.
> > This is the deal breaker. SCRAM without channel binding is like Coke Ze=
ro
> > without caffeine and mixed with water. Don't get me wrong, the work beh=
ind
> > is great.
> >=20
> >     But just a bit more is needed to make it really a big announcement =
and
> > provide real value to (I guess, mostly but very interesting) enterprise
> > customers, for which MITM and impersonating are big things. The good ne=
ws is
> > that adding channel binding is like inverse Paretto: a 20% of extra eff=
ort
> > (I bet significantly less) leads to 80% improvement.
>=20
> I don't see why channel binding is a big deal for enterprises because I
> assume they are already using SSL:

Channel binding should be used with SSL to ensure that there is no
man-in-the-middle attack being performed.  It's necessary when the
end-points aren't performing full, mutual, certificate-based
verification.

> I think the big win for SCRAM is the inability to replay md5 packets
> after recording 16k sessions (salt was only 32-bit, so a 50% chance of
> replay after 16 sessions), and storage of SHA256 hashes instead of MD5
> in pg_authid, though the value of that is mostly a check-box item
> because collisions are not a problem for the way we use MD5.

There are a lot of wins to having SCRAM implemented.  I disagree
strongly that securing PG from attacks based on latent information
gathering (backups which include pg_authid) is just a "check-box" item.

Thanks!

Stephen

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