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.

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