[dmarc-ietf] Lookup Limitations For Public Suffix Domains

Scott Kitterman <sklist@kitterman.com> Wed, 21 November 2018 07:37 UTC

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From: Scott Kitterman <sklist@kitterman.com>
To: dmarc@ietf.org
Date: Wed, 21 Nov 2018 02:37:19 -0500
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Subject: [dmarc-ietf] Lookup Limitations For Public Suffix Domains
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While we were discussing making draft-kitterman-dmarc-psd a working group 
item, the main discussion point was about the use of an IANA registry to 
identify participating public suffix domains.  I think it would be useful to 
consider what problems we were trying to solve and see if there are 
alternative approaches that address those requirements.

Also, while I think the discussion about a DMARC specific public boundary 
discovery mechanism was useful, and we should consider taking on that work, I 
think it's not closely coupled to Public Suffix Domains and should be 
discussed as a separate work item.

Goals:

1.  Minimize additional verifier burden for adding PSD DMARC support.  
Currently it requires consulting a locally stored, infrequently changing list 
and one additional DNS lookup only for participating public suffixes when 
there is no organizational domain DMARC record.

2.  Externalize signaling about PSD participation.  As discussed in the 
Privacy Considerations (section 4.1), we were concerned about the privacy 
implications of feedback on organizational domain traffic for organizational 
domains that don't participate in DMARC being inappropriately captured by 
public suffix operators.  In order to avoid this, we identified criteria for 
which public suffixes PSD DMARC would be appropriate for and require an 
external review to ensure those criteria are met.  No solution that's in DNS 
will address this part of the problem.

I believe that if there are alternatives that support both these requirements, 
then they should be seriously considered, we just didn't think of one when 
working up the draft.

Scott K