Re: [mile] Benjamin Kaduk's Discuss on draft-ietf-mile-xmpp-grid-09: (with DISCUSS and COMMENT)

Alexey Melnikov <aamelnikov@fastmail.fm> Thu, 24 January 2019 13:05 UTC

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From: Alexey Melnikov <aamelnikov@fastmail.fm>
To: Dave Cridland <dave@cridland.net>
Cc: Benjamin Kaduk <kaduk@mit.edu>, The IESG <iesg@ietf.org>, mile@ietf.org, mile-chairs@tools.ietf.org, draft-ietf-mile-xmpp-grid@ietf.org, mile-chairs@ietf.org
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Date: Thu, 24 Jan 2019 13:04:51 +0000
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Subject: Re: [mile] Benjamin Kaduk's Discuss on draft-ietf-mile-xmpp-grid-09: (with DISCUSS and COMMENT)
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Hi Dave,

On Thu, Jan 24, 2019, at 12:43 PM, Dave Cridland wrote:
> On Thu, 24 Jan 2019 at 12:04, Alexey Melnikov
> <aamelnikov@fastmail.fm>; wrote:>> Hi Benjamin,
>> > I also think this document does not adequately justify restricting
>> > to just>>  > the EXTERNAL and SCRAM families of SASL mechanisms;
>> 
>>  I want to push back on this. The document is adding new requirement
>>  on top of what RFC 6120 requires, this is effectively new mandatory
>>  to implement SASL mechanisms for use XMPP with grids. Ideally this
>>  would be a single SASL mechanism, but I think one password based and
>>  one X.509 based is a good compromise here.>> 
> 
> So I see Benjamin's point here. The document does introduce a new MTI
> SASL mechanism cohort of EXTERNAL, SCRAM-SHA1, and SCRAM-SHA-256. This
> is fine, but one has to wonder why we don't do this universallyI think any effort to update RFC 6120 needs to proceed independently: it
can't hold this document hostage.
> - I might try to address this. (RFC 6120 has an MTI of SCRAM-SHA1,
>   EXTERNAL, and PLAIN+TLS for comparison).> 
> But as Benjamin says, it also mandates their exclusive usage.
> From ยง8.3.1:> 
>    completing the TLS handshake.  The XMPP-Grid Controller MUST
>    authenticate the XMPP-Grid Platform either using the SASL EXTERNAL>    mechanism [RFC4422] or using the SASL SCRAM mechanism (with the
>    SCRAM-SHA-256-PLUS variant being preferred over the SCRAM-SHA-256
>    variant and SHA-256 variants [RFC7677] being preferred over SHA-1
>    varients [RFC5802]).  XMPP-Grid Platforms and XMPP-Grid Controllers> 
> (Also, typo in "varients").
> 
> There are, indeed, other SASL mechanisms which could be used to good
> effect here - and indeed weaker ones that might be appropriate in some
> circumstances. But, as written, the document prohibits these.
I suspect prohibition of others is not intentional. So what is the best
way of addressing this? Change the MUST to the SHOULD and possibly
change "MUST authenticate" to "SHOULD support"?
Best Regards,
Alexey