Re: [keyassure] CN/SAN matching (was: End entity certificate matching, trust anchors, and protocol-06)

Stephen Kent <kent@bbn.com> Wed, 30 March 2011 11:40 UTC

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Date: Wed, 30 Mar 2011 07:19:39 -0400
To: Peter Palfrader <peter@palfrader.org>
From: Stephen Kent <kent@bbn.com>
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Cc: keyassure@ietf.org, Paul Hoffman <paul.hoffman@vpnc.org>
Subject: Re: [keyassure] CN/SAN matching (was: End entity certificate matching, trust anchors, and protocol-06)
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At 11:14 AM +0200 3/30/11, Peter Palfrader wrote:
>On Mon, 21 Mar 2011, Paul Hoffman wrote:
>
>>  On Mar 21, 2011, at 6:04 AM, Peter Palfrader wrote:
>>  > Why is it needed in the first place?
>>
>>  That's a very good question. I don't feel that it is a "need", but it
>>  "makes some sense". That is, if I want to go to www.example.com, and I
>>  get an A record for www.example.com, and I get a TLSA record for
>>  _http._tcp.www.example.com, and I get a certificate that says "this
>>  key is associated with www.somethingelse.com"quot;, what does it mean?
>>
>>  I can see both ways: "it doesn't matter what the cert says, we are
>>  trusting the binding from the DNS" vs. "the cert needs to mean
>>  something"? Jakob and I have that text in because a number of people
>>  on the list were in the latter category, but it seems like a
>>  reasonable question to ask separately.
>
>I wonder if one approach here would be to require a match if, and only
>if, any naming attributes (CN, SubjectAltName) are in the certificate.
>
>If there are no CN and no SAN attributes in the certificate then that
>would be acceptable too.
>
>Cheers,
>Peter

A CN is a type of attribute in the Subject DN.  A SAN admits a 
variety of name types, some of which can have attributes. Do you mean 
to focus on DNS names as SANs or did you have a broader range of SANs 
in mind?

Steve