Re: [DNSOP] [Ext] I-D Action: draft-ietf-dnsop-svcb-https-05.txt

Brian Dickson <brian.peter.dickson@gmail.com> Thu, 20 May 2021 02:31 UTC

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In-Reply-To: <D712E09A-BE78-45C1-BA00-CA4AC5A78A12@isc.org>
From: Brian Dickson <brian.peter.dickson@gmail.com>
Date: Wed, 19 May 2021 19:31:36 -0700
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To: Mark Andrews <marka@isc.org>
Cc: Paul Wouters <paul@nohats.ca>, Ben Schwartz <bemasc=40google.com@dmarc.ietf.org>, dnsop <dnsop@ietf.org>
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Subject: Re: [DNSOP] [Ext] I-D Action: draft-ietf-dnsop-svcb-https-05.txt
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On Wed, May 19, 2021 at 7:15 PM Mark Andrews <marka@isc.org> wrote:

>
>
> > On 20 May 2021, at 11:52, Paul Wouters <paul@nohats.ca> wrote:
> >
> > On Wed, 19 May 2021, Ben Schwartz wrote:
> >
> >> So long as there are no registered protocol identifiers containing ","
> or "\\", zone file implementations MAY
> >> disallow these characters instead of implementing the `value-list`
> escaping procedure.
> >
> > Sorry, an implementor cannot predict the future of the IANA registry.
> They
> > can't write code to confirm to this requirement other than NOT allowing
> > the MAY.
> >
> > Even if they were silly enough to _first_ check the IANA registry before
> > parsing SVCB records, they would still have to write all the the parsing
> > code without CVE's for both cases, just in case the IANA registry would
> > gain these characters in the future.
>
> Or detect them and switch to key1=“…” instead of alpn=“…” when displaying
> entry would need to be using keyXXXX format until the software was
> upgraded.
>
> alpn=“h1\\,h2,h3” (or alpn=“h1\,h2,h3” I’m not sure where the consensus
> lies)
> vs key1=“\005h1,h2\002h3"
>

I don't understand why any of the comma-escaping is needed at all, honestly.

RFC1035 has the definition of <character-string> encoding:
A bunch of characters without any internal spaces, or
A string beginning with " and ending with ", and anything else in between
except " which must be escaped.

So, alpn=<character-string>[,<character-string>]* is unambiguous.
Restricting the character-string format used
to the kind surrounded by quotes, removes any ambiguity regarding commas.
Parsers need to be sufficiently well built to not treat commas internal to
character-string values as special.

No escaping of anything other than double-quote characters within a single
value (an ALPN) is needed.

Brian