Re: [dbound] draft-brotman-rdbd

Stephen Farrell <stephen.farrell@cs.tcd.ie> Mon, 01 April 2019 01:37 UTC

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To: "John R. Levine" <johnl@iecc.com>
Cc: dbound@ietf.org, "A. Schulze" <sca@andreasschulze.de>
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From: Stephen Farrell <stephen.farrell@cs.tcd.ie>
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Date: Mon, 1 Apr 2019 02:37:46 +0100
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Subject: Re: [dbound] draft-brotman-rdbd
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John,

On 01/04/2019 02:01, John R. Levine wrote:
>> If the public key is available with integrity (either via DNSSEC
>> for the relating domain or via caching) then signatures add some
>> evidence that the relationship is real.
> 
> But if I publish a DNSSEC signed record that says "this other domain
> is related to me" you get exactly the same level of assurance.

Disagree. Your "I" there is ambiguous, and I (meaning me,
personally:-) have explained before how that "exactly the
same" is incorrect. (See text marked "*" below for why.)

> 
> What does the extra signature provide that DNSSEC doesn't?

Sigh. I really have explained this. If email is not sufficient to get
that over, then perhaps we can wait 'till we're in the same room again?
I honestly have no clue how you don't understand this. I could totally
accept that you do understand it, but consider it wrong, (in which case
I'd only consider you mistaken,:-) But given your and my history with
e.g. DKIM, I really am extremely surprised that you do not appear to
understand what I'm tying to explain.

But, see the text marked "*" for why.

> Conversely, if it's not DNSSEC signed, publishing a fake "this other
> domain" record is exactly as hard as publishing a fake public key
> record.

"*": For the 3rd or 4th time, and with feeling: Publishing is not the
same as having a relying-party treat a signature differently. As you'll
no doubt have noted, I did say "with integrity" above, which is more
than just "publishing." That kind of integrity for a public key can
be provided via caching, or DNSSEC. Once one has that, then signatures
are not at all the same as if one were to have only freshly read the
public key from the DNS. For example, if a relying-party has seen the
same public key used for a relating domain N times or for N years, and
sees that public key used again, then that relying-party can treat
that differently, compared to a public key just seen now, without any
DNSSEC. DNSSEC, if deployed for the relating domain (not the related
domain), can provide some similar level of assurance about the public
key.

That trust-model for signatures is entirely as was done for DKIM. I
believe you do understand that trust-model for keys. If not, I would
be surprised but happy to explain yet again.

I do hope that is finally clear but suspect it'll not prove to be.
(Whilst remaining surprised that this could be a surprise to you.)
And I'll nonetheless be happy to try explain for a 5th or 6th time;-)

Cheers,
S.


> 
> R's, John
> 
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