Re: [dane] Digest Algorithm Agility discussion

Peter Palfrader <peter@palfrader.org> Mon, 24 March 2014 15:34 UTC

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Date: Mon, 24 Mar 2014 16:33:58 +0100
From: Peter Palfrader <peter@palfrader.org>
To: Paul Wouters <paul@nohats.ca>
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Subject: Re: [dane] Digest Algorithm Agility discussion
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On Mon, 24 Mar 2014, Paul Wouters wrote:

> On Sun, 23 Mar 2014, Viktor Dukhovni wrote:
> 
> >when the TLSA records are entirely unusable, and in keeping with Tony's
> >original work on the SRV draft, the client reverts to legacy
> >mandatory (practically always unauthenticated) TLS.
> 
> That's unfortunate. Perhaps it depends on the definition of "unusable",
> but if all TLSA records for instance fail the RRSIG validation, I would
> hope that postfix would abort delivery attempts and definately _not_
> fallback to unauthenticated TLS.

2.1. of draft-ietf-dane-smtp-with-dane-07:
}  When a DNS lookup failure (error or "bogus" or "indeterminate" as
}  defined above) prevents an SMTP client from determining which SMTP
}  server or servers it should connect to, message delivery MUST be
}  delayed.

Unusable thus would mean we don't know or like the digest type, or
usage, selector, or matching type.

The 07 dane smtp draft further says:
}  A Secure non-empty TLSA RRset where all the records are unusable:  A
}     connection to the MTA MUST be made via TLS, but authentication is
}     not required.  Failure to establish an encrypted TLS connection
}     MUST result in falling back to the next SMTP server or delayed
}     delivery.

Cheers,
-- 
                           |  .''`.       ** Debian **
      Peter Palfrader      | : :' :      The  universal
 http://www.palfrader.org/ | `. `'      Operating System
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