Re: [keyassure] Objective: Restrictive versus Supplementary Models

"Richard L. Barnes" <rbarnes@bbn.com> Thu, 31 March 2011 09:13 UTC

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From: "Richard L. Barnes" <rbarnes@bbn.com>
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Date: Thu, 31 Mar 2011 11:15:31 +0200
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To: Paul Wouters <paul@xelerance.com>
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Subject: Re: [keyassure] Objective: Restrictive versus Supplementary Models
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>>> If the attacker injects fake dns records pointing to a fake server, they
>>> can include a dane rr.  It only makes the attack slightly harder, doesn't it?
>> 
>> Yes, but as ekr pointed out, injecting fake DANE RRs can only cause the connection to fail, it won't result in the client connecting to a bogus server.   That's why it's RECOMMENDED instead of REQUIRED.
> 
> Not if you are a MITM on the wire as well (more star bucks wifi use cases) and
> you're directing the user to your own website with a dane rr matching public key.

You're confusing the "Cert Lock" and "Install TA" use cases.  If all the server doing is "Cert Lock", then the bogus DANE record will simply cause the client to reject the server's cert and the connection to fail.  In the "Install TA" case, DNSSEC would be REQUIRED, for exactly the reason you note.

--Richard