Subject: [dns-privacy] Brian Haberman's Yes on draft-ietf-dprive-dns-over-tls-07: (with COMMENT)

From: "Brian Haberman" <[email-masked]>
Date: Tue, 08 Mar 2016 07:38:56 -0800

Brian Haberman has entered the following ballot position for
draft-ietf-dprive-dns-over-tls-07: Yes

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COMMENT:
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I am a definite Yes on this work, but just have a couple of comments...

* Section 3.1 says "By mutual agreement with its server, the client MAY,
instead, use a port other than port 853 for DNS-over-TLS.  Such an other
port MUST NOT be port 53..." It would be useful to *briefly* explain the
MUST NOT. If it is by mutual agreement, what's the harm?

* Section 3.2 uses the SPKI acronym before it is expanded in section
4.2.

* I do not understand the last sentence of section 3.2, especially the
"SHOULD".

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From: "Wessels, Duane" <[email-masked]>
Date: Tue, 8 Mar 2016 22:35:39 +0000

Hi Brian,

> On Mar 8, 2016, at 7:38 AM, Brian Haberman <[email-masked]> wrote:
> 
> 

This text was recently added during a review of 5966bis (DNS-over-TCP)
where there was a concern that neither that nor this document said anything
about not mixing cleartext and ciphertext.

I suppose another reason is that middleware boxes might want to "inspect"
port 53 and TLS over port 53 will fail.

Would you be okay with adding this sentence or similar?  

   Use of port 53 for DNS-over-TLS is prohibited
   because mixing cleartext and ciphertext can result in false privacy.

> * Section 3.2 uses the SPKI acronym before it is expanded in section

Fixed.

> * I do not understand the last sentence of section 3.2, especially the

You are referring to this sentence:

     At this point, normal DNS queries SHOULD take place.

I believe it is sort of an artifact from the time when the draft included
a "STARTTLS for DNS" option whereby an unencrypted TCP connection could
be upgraded.  Dropping the sentence is fine with me.  

DW

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From: John Heidemann <[email-masked]>
Date: Tue, 08 Mar 2016 22:14:17 -0800

>   because mixing cleartext and ciphertext can result in false privacy.

Wrt this comment, I would suggest:

   Use of port 53 for DNS-over-TLS is prohibited to avoid
   complication in selecting use or non-use of TLS,
   and to reduce risk of downgrade attacks.

to be more explicit about "false privacy".  (Multiple other reviewers
commented on both complexity and downgrade risks---my understanding is
that is why we ended up so strict, and without STARTTLS.)

("complications" means in implementation, but I omitted that word to
keep it short.)

The other comments and changes all look good to me.

   -John

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From: Brian Haberman <[email-masked]>
Date: Wed, 9 Mar 2016 08:03:36 -0500

Hi Duane,

>    because mixing cleartext and ciphertext can result in false privacy.

A spec really can't prohibit somebody from doing something, but I get
the rationale.  How about:

The use of port 53 for DNS-over-TLS is not recommended since mixing
cleartext and ciphertext could result in interoperability issues or a
reduction in privacy.

> be upgraded.  Dropping the sentence is fine with me.  

Dropping the sentence works for me.

Regards,
Brian

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From: Brian Haberman <[email-masked]>
Date: Wed, 9 Mar 2016 08:22:09 -0500

Hi John,

>    and to reduce risk of downgrade attacks.

I missed this follow-up prior to responding to Duane...

My suggestion is replacing "prohibited" with "not recommended".

Regards,
Brian

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From: John Heidemann <[email-masked]>
Date: Wed, 09 Mar 2016 09:19:26 -0800

On Wed, 09 Mar 2016 13:23:19 +0000, Warren Kumari wrote: 
>On Wed, Mar 9, 2016 at 1:22 PM Brian Haberman <[email-masked]> wrote:
>
>    Hi John,
>   
>No hats here, but I like that.

I checked in with this text:

          This recommendation against use of port 53 for DNS-over-TLS
	  is to avoid
          complication in selecting use or non-use of TLS,
          and to reduce risk of downgrade attacks.

to avoid the "...not recommended to avoid..." double negative.

   -John

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From: "Wessels, Duane" <[email-masked]>
Date: Wed, 9 Mar 2016 17:36:24 +0000

> On Mar 9, 2016, at 9:19 AM, John Heidemann <[email-masked]> wrote:
> 
>>> 

Thanks John.  If everyone is okay with that, then I believe we have addressed
all of Brian's comments?

DW

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From: Barry Leiba <[email-masked]>
Date: Wed, 9 Mar 2016 17:39:23 +0000

> to avoid the "...not recommended to avoid..." double negative.

That's actually not a double negative, but a shortened (and confusing)
version of "...is not recommended, in order to avoid...".  In any
case, your rewording is mighty fine, and I don't recommend that you
not avoid leaving it unchanged.[1]

Barry

[1] It was a challenge to find a quadruple negative that didn't sound
*too* contrived.

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From: Brian Haberman <[email-masked]>
Date: Wed, 9 Mar 2016 13:00:01 -0500

Hi Duane,

> Thanks John.  If everyone is okay with that, then I believe we have addressed

As far as I am concerned.

Thanks,
Brian