Re: SCRAM authentication, take three

On 04/07/2017 10:38 AM, Magnus Hagander wrote:
> So here's a wild idea. What if we just call it "sha256"? Does the user
> actually care about it being scram, or is scram just an implementation
> detail for them? That way when the next one shows up, it'll be sha512 or
> whatever. It happens to use scram under the hood, but does the user have to
> or does the user want to care about that?
>
> (One could argue the same way that the user shouldn't have to or want to
> care about the hashing algorithm -- but if that's the case then we should
> only have one entry, it would be "scram", and the system would decide from
> there. And I think this discussion already indicates we don't think this is
> enough)

I think the "SCRAM" part is more important than "SHA-256", so -1 on that.

The main against using just "scram" is that it's misleading, because we
implement SCRAM-SHA-256, rather than SCRAM-SHA-1, which was the first
SCRAM mechanism, commonly called just SCRAM. As long as that's the only
SCRAM variant we have, that's not too bad, but it becomes more confusing
if we ever implement SCRAM-SHA-512 or SCRAM-something-else in the
future. That's the point Noah made, and it's a fair point, but the
question is whether we consider that to be more important than having a
short name for what we have now.

>> The channel binding aspect is actually more important to think about right
>> now, as that we will hopefully implement in the next release or two.
>>
>> In [1], Michael wrote:
>>
>>> There is also the channel binding to think about... So we could have a
>>> list of keywords perhaps associated with SASL? Imagine for example:
>>> sasl $algo,$channel_binding
>>> Giving potentially:
>>> sasl scram_sha256
>>> sasl scram_sha256,channel
>>> sasl scram_sha512
>>> sasl scram_sha512,channel
>>> In the case of the patch of this thread just the first entry would
>>> make sense, once channel binding support is added a second
>>> keyword/option could be added. And there are of course other methods
>>> that could replace SCRAM..
>>
>> It should also be possible to somehow specify "use channel binding, if the
>> client supports it".
>
> Is that really a type of authentication? We already hvae the idea of
> authentication method options, used for most other things except md5 which
> doesn't have any. So it could be "sha256 channelbind=on", "sha256
> channelbind=off" or "sha256 channelbind=negotiate" or something like that?

Technically, the channel-binding variant is a separate SASL mechanism,
i.e. it has a separate name, SCRAM-SHA-256-PLUS. I'm not sure if
users/admins think of it that way.

>> I don't think "sasl" is interesting to a user, it's the actual mechanisms
>> (e.g "scram-sha256") that matter. So I'd suggest that we allow a list of
>> algorithms in the method field. If we go with the longer "scram-sha-256"
>> name, it would look like this:
>>
>> # TYPE DATABASE USER ADDRESS METHOD
>> host all all example.com scram-sha-256-plus,
>> scram-sha-256
>>
>> The problem again is that those names are quite long. Is that OK?
>
> Not sure if it would be doable in the code, but we could also have:
> host all all example.com scram method=sha256plus,sha256
>
> or something like that. Which would fit within the current syntax of the
> file. But I think it might not be enough, because then you couldn't have
> two entries with different scram methods for the same combination of the
> other fields -- the hba *matching* doesn't look at the options fields.

You can't have two entries with the same type+database+user+address
combination, period. (Or if you do, the second one is ignored.)

- Heikki