Subject: Fwd: Automatic key verification / CERT in DNS / RFC4398 (Was: [Announce] GnuPG 1.4.3 released)

From: Brad Knowles <[email-masked]>
Date: Wed, 5 Apr 2006 02:17:43 -0500

At 10:28 PM -0400 2006-04-04, Danny Mayer wrote:

>  These three lead to one big question though:
>    Can we start doing automatic key verification for mail !?

	See DKIM.

>  This all though leads to a concern on the placing of the CERTS. Having a
>  large user base would mean that one has say 600k records or more in the
>  main zone for a domain, which gets reloaded every now and then when one
>  needs to update it.

	Think about ten million users, or fifty million.  Each user 
having several hundred bytes (or even several KB) of data stored for 
them.  Stored in the DNS.  In a single flat zone.  Bad idea.  Like, 
really bad idea.  Like, one of the worst DNS-related ideas I think 
I've ever heard of, at least in a very long time.

	And it shares most of the same problems in this respect with 
DKIM, if you try to push DKIM to process data at the individual level 
as opposed to the domain level.

	Very highly non-scalable.

>  Of course this will also require a lot of software to make it working,
>  but this is going in the right direction! :)

	Possibly, but I'm not convinced.  There's lots of scalability 
issues that need to be given some serious thought before you just 
leap into the fray and start spraying about large DNS records for 
each user, regardless of any other factors that are involved.

-- 
Brad Knowles, <[email-masked]>

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."

     -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
     Assembly to the Governor, November 11, 1755

  LOPSA member since December 2005.  See <http://www.lopsa.org/>.

---

From: Werner Koch <[email-masked]>
Date: Wed, 05 Apr 2006 12:30:54 +0200

> 	See DKIM.

DKIM just doesn't work - at least not as described in the I-D I am
aware of.  The canonicalization rules needed for MIME are broken and
may be used to inject a faked message within a DKIM signed one.  The
recipient (or MTA) will see that the mail verified okay but the actual
content shown is the faked one.  See Thomas Roessler's "noswp
considred harmful"[1].

> 	Very highly non-scalable.

I doubt that.  A PKA record like

  "v=pka1;fpr=A4D94E92B0986AB5EE9DCD755DE249965B0358A2"

can be squeezed into less that 32 bytes with a dedicated RR type.  If
you don't want to use general keyservers, add the space for an URL.
The latter may even be optimized by extending the system to define URL
shortcuts like looking up the default key distribution method of the
domain (e.g. by using HTTP).

And don't forget that an URL in the PKA record has the additional
benefit of allowing for opportunistic encryption.

Salam-Shalom,

   Werner

[1]
http://www.mhonarc.org/archive/cgi-bin/mesg.cgi?a=ietf-mailsig&i=20050720080547.GA8239%40raktajino.does-not-exist.org

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From: Jeroen Massar <[email-masked]>
Date: Wed, 05 Apr 2006 13:57:03 +0200

> >    Can we start doing automatic key verification for mail !?

Which is not there yet and will take the coming X years to be designed,
developed and deployed. While PGP is working already for several years
and has been proven to work very reliably.

> I've ever heard of, at least in a very long time.

Checking http://dailychanges.com/ status of domains on 4/4/2006:
49,340,982 .com
7,425,723  .net

etc. so what was the issue again of storing a couple of million records
in DNS? If you claim it is a 'bad idea' then why does the CERT record
exist at all when it has the intentions of allowing PGP keys to be
stored? ;)

Using for instance nsd (http://www.nlnetlabs.nl/nsd/) should not pose a
problem in serving these amounts of contents.

It is more a 'separation' question I am asking, so that one has a
subzone for these records, which will allow one to have say 3
nameservers, which are registered at the tld servers thus can't easily
be changed, for example.org but have 20, which you stuff in example.org,
handling the load for _certs.example.org where the CERTS are stored.
It's a choice item giving the possility of doing it.

> 	Very highly non-scalable.

See below and also in my original message...

> each user, regardless of any other factors that are involved.

Which is why I noted that one could have a single pgp key for a complete
domain could cover all the cases where one doesn't have the enduser
signing the messages but a central system doing it for them. Which is in
effect what DKIM does but allowing the freedom to have per-user keys
too.

Eg large sites like hotmail/gmail/yahoo/whatever could have a 'websign
key' where the outbound webengine signs the message for the user.
Presto, 60M users served with one key. This situation is the case for a
large percentage of the ISP's around the globe, especially as they
should be 'forcing' their clients to send outbound mail over their SMTP
gateways (using submit :) instead of using the one which is acting like
an open relay.

And the good parts:
 - this can work today
 - MTA or MUA only have to do a PGP verification of the message
 - very easy to deploy and setup
 - no transition needed, just deploy at the ISP and it works.

of course many/all sites have to participate otherwise it doesn't have
much effect, though one could say "drop/bounce anything not signed" at a
certain point.

I don't care if we go for PKA or CERT records as long as the silly
spoofing of source addresses gets halted. Spam and virusses are easily
discarded using things like SpamAsssassin and ClamAV etc, but bounces
might be legit so one still gets those and lots of them from all the
virusses and spams spoofing your email address toward non-existent
addresses or folks with auto-replies etc.

Greets,
 Jeroen

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From: Ólafur Guðmundsson /DNSEXT co-chair <[email-masked]>
Date: Wed, 05 Apr 2006 10:58:41 -0400

> > At 10:28 PM -0400 2006-04-04, Danny Mayer wrote:

Please remove namedroppers from future postings on this tread.
I'm not approving any messages as the discussion is about possible
DNS operational issues, not DNS protocol issues.

         Olafur (namedroppers moderator of the day)

---

From: Jeroen Massar <[email-masked]>
Date: Wed, 05 Apr 2006 19:13:42 +0200

On Wed, 2006-04-05 at 10:58 -0400, Ólafur Guðmundsson /DNSEXT co-chair
> DNS operational issues, not DNS protocol issues.

The discussion which led from it is indeed, but my original question,
though at the bottom of the mail was:

8<--------------------------------------------
This all though leads to a concern on the placing of the CERTS. Having a
large user base would mean that one has say 600k records or more in the
main zone for a domain, which gets reloaded every now and then when one
needs to update it. It would IMHO be better to be able to off load those
records to say _cert.example.org. Which has several benefits, one can
then run their normal DNS adminstration and delegate the CERT records to
a dedicated DNS server set which can handle the updates easier or simply
runs out of a DNSBackend. This will also be easier management wise with
DNSSEC I expect and remove the strain from the main boxes, which
currently might have maybe upto 100 RR's on average in a zone,
especially in the case of webhosting farms where one only specifies the
www.example.org and nothing else.
------------------------------------------->8

Altough this is also more or less an operational question, the question
is very related to dnsext as the CERT record has been defined here and
RFC4398 defines that person CERT's can be found under
<user>.example.org.

This was the point I wanted to clear up, that, indeed for ops purposes,
one rather have a subzone. This is again a protocol related thing as
when one sticks all the CERTs in the main zone, this will grow and you
will have to take into account keyrotation for DNSSEC...

If I am totally of base, then simply drop the discussion of course.

Greets,
 Jeroen

-------

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From: Paul Vixie <[email-masked]>
Date: Wed, 05 Apr 2006 17:19:46 +0000

also note that dns operational issues are welcome on
[email-masked], which is a mailman-run
list whose url is lists.oarci.net/mailman/listinfo/.