Re: Some thoughts about SCRAM implementation

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:

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

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.

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

+ As you are, so once was I. As I am, so you will be. +
+ Ancient Roman grave inscription +