Subject: Re: Add "password_protocol" connection parameter to libpq
To: Tom Lane <tgl@sss.pgh.pa.us>, Stephen Frost <sfrost@snowman.net>
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Cc: Jeff Davis <pgsql@j-davis.com>, "Jonathan S. Katz"
 <jkatz@postgresql.org>, Michael Paquier <michael@paquier.xyz>,
 pgsql-hackers@postgresql.org
From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
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Message-ID: <f433a63f-802d-bb29-7df7-8cb6e80bdc43@2ndquadrant.com>
Date: Mon, 12 Aug 2019 19:46:41 +0200
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On 2019-08-12 19:26, Tom Lane wrote:
> What problem do we actually need to solve here?
> 
> If the known use-case is just "don't send my password in the clear",
> maybe we should just change libpq to refuse to do that, ie reject
> plain-password auth methods unless SSL is on (except maybe over
> unix sockets?).  Or invent a bool connection option that enables
> exactly that.

There are several overlapping problems:

1) A downgrade attack by a malicious server.  The server can collect
passwords from unsuspecting clients by just requesting some weak
authentication like plain-text or md5.  This can currently be worked
around by using SSL with server verification, except when considering
the kind of attack that channel binding is supposed to address.

2) A downgrade attack to evade channel binding.  This cannot currently
be worked around.

3) A user not wanting to expose a weakly hashed password to the
(otherwise trusted) server.  This cannot currently be done.

4) A user not wanting to send a password in plain text over the wire.
This can currently be done by requiring SSL.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services