Re: Password identifiers, protocol aging and SCRAM protocol

On Mon, Dec 12, 2016 at 11:39 PM, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:
> A few couple more things that caught my eye while hacking on this:
>
> 1. We don't use SASLPrep to scrub username's and passwords. That's by
> choice, for usernames, because historically in PostgreSQL usernames can be
> stored in any encoding, but SASLPrep assumes UTF-8. We dodge that by passing
> an empty username in the authentication exchange anyway, because we always
> use the username we got from the startup packet. But for passwords, I think
> we need to fix that. The spec is very clear on that:
>
>> Note that implementations MUST either implement SASLprep or disallow
>> use of non US-ASCII Unicode codepoints in "str".
>
> 2. I think we should check nonces, etc. more carefully, to not contain
> invalid characters. For example, in the server, we use the read_attr_value()
> function to read the client's nonce. Per the spec, the nonce should consist
> of ASCII printable characters, but we will accept anything except the comma.
> That's no trouble to the server, but let's be strict.
>
> To summarize, here's the overall TODO list so far:
>
> * Use SASLPrep for passwords.
>
> * Check nonces, etc. to not contain invalid characters.
>
> * Derive mock SCRAM verifier for non-existent users deterministically from
> username.
>
> * Allow plain 'password' authentication for users with a SCRAM verifier in
> rolpassword.
>
> * Throw an error if an "authorization identity" is given. ATM, we just
> ignore it, but seems better to reject the attempt than do something that
> might not be what the client expects.
>
> * Add "scram-sha-256" prefix to SCRAM verifiers stored in
> pg_authid.rolpassword.
>
> Anything else I'm missing?
>
> I've created a wiki page, mostly to host that TODO list, while we hack this
> to completion: https://wiki.postgresql.org/wiki/SCRAM_authentication. Feel
> free to add stuff that comes to mind, and remove stuff as you push patches
> to the branch on github.

Based on the current code, I think you have the whole list. I'll try
to look once again at the code to see I have anything else in mind.
Improving the TAP regression tests is also an item, with SCRAM
authentication support when a plain password is stored.
--
Michael