Re: Some thoughts about SCRAM implementation

On Tue, Apr 11, 2017 at 08:58:30PM -0400, Stephen Frost wrote:
> > > 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.

And which enterprises are using SSL without certificates? And I thought
channel binding required certificates anyway, e.g.:

https://en.wikipedia.org/wiki/Salted_Challenge_Response_Authentication_Mechanism#Channel_binding

For instance, for the tls-server-end-point channel binding, it is the
server's TLS certificate.

> > 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.

Well, they have the entire backup so I don't think cracking the password
is a huge win, though the password does potentially give them access to
future data. And it prevents them from reusing the password on another
server, but _again_, I still think the big win is to prevent replay
after 16k packets are sniffed.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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