Re: MD5 authentication needs help

Catching up here ...

On 03/03/2015 06:01 PM, Bruce Momjian wrote:
> It feels like MD5 has accumulated enough problems that we need to start
> looking for another way to store and pass passwords. The MD5 problems
> are:
>
> 1) MD5 makes users feel uneasy (though our usage is mostly safe)
>
> 2) The per-session salt sent to the client is only 32-bits, meaning
> that it is possible to reply an observed MD5 hash in ~16k connection
> attempts.

Seems like we could pretty easily increase the size of the salt. Of
course, that just increases the required number of connection attempts,
without really fixing the problem.

> 3) Using the user name for the MD5 storage salt allows the MD5 stored
> hash to be used on a different cluster if the user used the same
> password.

This is a feature as well as a bug. For example, pgBouncer relies on
this aspect of md5 auth.

> 4) Using the user name for the MD5 storage salt causes the renaming of
> a user to break the stored password.

Wierdly, in 17 years of Postgres, I've never encountered this issue.

So, are we more worried about attackers getting a copy of pg_authid, or
sniffing the hash on the wire?

--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com