Re: SCRAM authentication, take three

Speaking about flaws, it looks like there is a memory leak in
array_to_utf procedure - result is allocated twice.

On Mon, Feb 20, 2017 at 02:51:13PM +0300, Aleksander Alekseev wrote:
> Hi!
>
> Currently I don't see any significant flaws in these patches. However I
> would like to verify that implemented algorithms are compatible with
> algorithms implemented by third party.
>
> For instance, for user 'eax' and password 'pass' I got the following
> record in pg_authid:
>
> ```
> scram-sha-256:
> xtznkRN/nc/1DQ==:
> 4096:
> 2387c124a3139a276b848c910f43ece05dd670d0977ace4f20d724af522312e4:
> 5e3bdd6584880198b0375acabd8754c460af2389499f71a756660a10a8aaa843
> ```
>
> Let's say I would like to implement SCRAM in pure Python, for instance
> add it to pg8000 driver. Firstly I need to know how to generate server
> key and client key having only user name and password. Somehow like
> this:
>
> ```
> >>> import base64
> >>> import hashlib
> >>> base64.b16encode(hashlib.pbkdf2_hmac('sha256', b'pass',
> ... base64.b64decode(b'xtznkRN/nc/1DQ=='), 4096))
> b'14B90CFCF690120399A0E6D30C60DD9D9D221CD9C2E31EA0A00514C41823E6C3'
> ```
>
> Naturally it doesn't work because both SCRAM_SERVER_KEY_NAME and
> SCRAM_CLIENT_KEY_NAME should also be involved. I see PostgreSQL
> implementation just in front of me but unfortunately I'm still having
> problems calculating exactly the same server key and client key. It makes
> me worry whether PostgreSQL implementation is OK.
>
> Could you please give an example of how to do it?
>
> On Mon, Feb 20, 2017 at 03:29:19PM +0900, Michael Paquier wrote:
> > On Sun, Feb 19, 2017 at 10:07 PM, Michael Paquier
> > <michael(dot)paquier(at)gmail(dot)com> wrote:
> > > There is something that I think is still unwelcome in this patch: the
> > > interface in pg_hba.conf. I mentioned that in the previous thread but
> > > now if you want to match a user and a database with a scram password
> > > you need to do that with the current set of patches:
> > > local $dbname $user scram
> > > That's not really portable as SCRAM is one protocol in the SASL
> > > family, and even worse in our case we use SCRAM-SHA-256. I'd like to
> > > change pg_hba.conf to be as follows:
> > > local $dbname $user sasl protocol=scram_sha_256
> > > This is extensible for the future, and protocol is a mandatory option
> > > that would have now just a single value: scram_sha_256. Heikki,
> > > others, are you fine with that?
> >
> > I have implemented that as 0009 which is attached, and need to be
> > applied on the rest of upthread. I am not sure if we want to make the
> > case where no protocol is specified map to everything. This would be a
> > tricky support for users in the future if new authentication
> > mechanisms for SASL are added in the future.
> >
> > Another issue that I have is: do we really want to have
> > password_encryption being set to "scram" for verifiers of
> > SCRAM-SHA-256? I would think that scram_sha_256 makes the most sense.
> > Who knows, perhaps there could be in a couple of years a SHA-SHA-512..
> >
> > At the same time, attached is a new version of 0008 that implements
> > SASLprep, I have stabilized the beast after fixing some allocation
> > calculations when converting the decomposed pg_wchar array back to a
> > utf8 string.
> > --
> > Michael
>
> --
> Best regards,
> Aleksander Alekseev

--
Best regards,
Aleksander Alekseev