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Re: [TLS] Eric Rescorla's Discuss on draft-ietf-tls-dnssec-chain-extension-06: (with DISCUSS and COMMENT)

Nico Williams <nico@cryptonector.com> Wed, 28 February 2018 20:07 UTC

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Date: Wed, 28 Feb 2018 14:07:10 -0600
From: Nico Williams <nico@cryptonector.com>
To: Shumon Huque <shuque@gmail.com>
Cc: Viktor Dukhovni <viktor@dukhovni.org>, The IESG <iesg@ietf.org>, draft-ietf-tls-dnssec-chain-extension@ietf.org, TLS WG <tls@ietf.org>, tls-chairs <tls-chairs@ietf.org>
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References: <CABcZeBOST2X0-MH2hhzpPJaUkbY++udsUV1bMnMhH2V2wQRPmA@mail.gmail.com> <CAHPuVdUs7mUJiqZjFjLDCNmHHGR9AP-g5YaLLbJj-zkDKd=_-w@mail.gmail.com> <alpine.LRH.2.21.1802211425260.7767@bofh.nohats.ca> <CAHPuVdX=_6b5g572-T-9Ccwek-WwL11KdTVwV9oNC9LaO5=0=Q@mail.gmail.com> <alpine.LRH.2.21.1802260913290.9977@bofh.nohats.ca> <70D42B5C-7FF9-49C1-95D4-13FDC611FF96@dukhovni.org> <CAHPuVdU8boBpYO3QutJgawH-54fKD+R9PaaT-5yWE+y2t+BwwA@mail.gmail.com> <CAHPuVdWhEnYxcLUzs-zbnKiN0zj+WO-7_cK2EobS1Gipurk7CQ@mail.gmail.com> <20180227233610.GD8921@localhost> <20180227233854.GE8921@localhost>
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Subject: Re: [TLS] Eric Rescorla's Discuss on draft-ietf-tls-dnssec-chain-extension-06: (with DISCUSS and COMMENT)
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IF there's an objection to modifying the extension in order to add a
pin-to-DANE TTL field, I would propose the following instead:

    Make the pin-to-DANE be "forever" but make it so it can easily be
    cleared if DANE is undeployed for the service.


That would look like this:

 - if the server sends the extension with a valid DANE RR chain

   -> pin to DANE (no TTL needed; see below)


 - if the server sends the extension with a non-existence proof for DANE

   -> clear the PIN to DANE


 - if the server sends the extension with proof that an intermediate
   domain is not signed

   -> clear the PIN to DANE

This has the great benefit that it is simple.

Also, I'm not at all sure that a pin TTL is actually useful.  If I know
bar.foo.example. supports DANE, why would I want to asynchronously stop
expecting it to use DANE when it could just tell me (with a suitable
proof)?

Nico
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