Re: [HACKERS] SCRAM authentication, take three

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
>  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