Re: Interpreting DNSSEC was Re: [dnsext] flip-flopping secure and unsecure DNAME/CNAME

Michael StJohns <mstjohns@comcast.net> Thu, 23 October 2008 16:31 UTC

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Date: Thu, 23 Oct 2008 12:25:06 -0400
To: Ben Laurie <ben@links.org>
From: Michael StJohns <mstjohns@comcast.net>
Subject: Re: Interpreting DNSSEC was Re: [dnsext] flip-flopping secure and unsecure DNAME/CNAME
Cc: namedroppers@ops.ietf.org
In-Reply-To: <49005921.2090108@links.org>
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At 06:59 AM 10/23/2008, Ben Laurie wrote:
>Michael StJohns wrote:
>
>I don't understand the rationale behind all this complication.
>
>If I chose to point a DNAME at an unsecured domain, then that was my
>choice, and I should live with it. If I don't want the domain to be
>unsecured, then I should either not delegate to it, or ensure it is
>secured by non-protocol means (e.g. by owning the domain myself, by
>contract, by sufficient purchase of beer for the domain owner, etc.)

Hi Ben -

One of the problem we get with DNS is that there are two views of the data (at least) - the publisher's, and the resolver's views. DNSSEC makes this more complicated by the presence or absence of certain trust anchors.

As publisher, I have a signed domain, and as publisher, I publish a DNAME also pointing at a signed domain.  I've done my due diligence as you suggest - I even own the target zone.

As resolver, I get a trust anchor for the first domain (more probably for a parent of the domain), but I don't have any a priori information that the target domain is also signed (or even that I had a redirect to that zone), so I don't know to get a trust anchor for it.  There's no way of encoding in DNS/DNSSEC the publishers security intentions with respect to the complete DNAME chain.  This leads to the problem where the publisher thought it was delegating into a signed zone, but the resolver thought the zone was unknown (no superior trust anchor).  The resolver has no way of telling that the publisher really thought this zone was signed and that the resolver should return a BOGUS answer if the target zone wasn't.

Answering Ed's question about inconsistency here: In a resolution without indirect records (e.g. DNAME, CNAME, MX, etc), the resolvers expectation about the security state of the answer are originally set by the presence or absence of a trust anchor and, assuming the trust anchor is present, that expectation changes only upon proof that it should (e.g. signed delegation into unsigned zone).  With DNAME, once the resolver starts doing lookups in the target zone, it restarts its expectation of the state of the answer based on what it knows about trust anchors for the target.  There is no chain of proof possible from the DNAME zone to the target zone in this model.


My suggestions are an attempt to provide a chain of proof from the original trust anchor (provided by the DNAME publisher or its parent) through to the final answer.  If that chain of proof validates, the resolver can say something useful about the entire answer chain  and the final answer and I think that's the only case in which this is true.  The case where the resolver just happens to have trust anchors for the DNAME zone and all of the target zones says useful things about each individual zone lookup, but not about the compound answer (I can elaborate here about DNAME publisher expectations and target zone publisher actions if necessary).


>-- 
>http://www.apache-ssl.org/ben.html           http://www.links.org/
>
>"There is no limit to what a man can do or how far he can go if he
>doesn't mind who gets the credit." - Robert Woodruff



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