Re: Some thoughts about SCRAM implementation

Bruce,

* Bruce Momjian (bruce(at)momjian(dot)us) wrote:
> On Tue, Apr 11, 2017 at 02:53:24PM +0200, Álvaro Hernández Tortosa wrote:
> > 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 question.
> > And bring some added benefits, true. So its "better". But the real gain
> > comes from using channel binding, which avoids impersonation, MITM attacks.
> > This is the deal breaker. SCRAM without channel binding is like Coke Zero
> > without caffeine and mixed with water. Don't get me wrong, the work behind
> > is great.
> >
> > 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 news is
> > that adding channel binding is like inverse Paretto: a 20% of extra effort
> > (I bet significantly less) leads to 80% improvement.
>
> 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