Re: [Doh] [dns-privacy] [DNSOP] New: draft-bertola-bcp-doh-clients

Eric Rescorla <ekr@rtfm.com> Tue, 12 March 2019 15:58 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Tue, 12 Mar 2019 08:58:12 -0700
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To: "Konda, Tirumaleswar Reddy" <TirumaleswarReddy_Konda@mcafee.com>
Cc: "doh@ietf.org" <doh@ietf.org>, "dnsop@ietf.org" <dnsop@ietf.org>, "dns-privacy@ietf.org" <dns-privacy@ietf.org>, Vittorio Bertola <vittorio.bertola=40open-xchange.com@dmarc.ietf.org>, Stephen Farrell <stephen.farrell@cs.tcd.ie>
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Subject: Re: [Doh] [dns-privacy] [DNSOP] New: draft-bertola-bcp-doh-clients
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On Tue, Mar 12, 2019 at 8:51 AM Konda, Tirumaleswar Reddy <
TirumaleswarReddy_Konda@mcafee.com> wrote:

> Hi Eric,
>
>
>
> In TLS 1.2, it is possible for firewalls to inspect the TLS handshake, and
> white-list, black-list and grey-list TLS session based on the server
> identity. In other words, middleboxes are conditionally acting as TLS
> proxies to specific servers (categorized in the grey-list).
>
With TLS 1.3 and encrypted SNI, the middle box now has to act as a TLS
> proxy for all the flows.
>

It would be most useful not to conflate TLS 1.3 and ESNI.

In ordinary TLS 1.3, the SNI is in the clear but the server cert is not.
However, importantly, even in TLS 1.2, the server certificate is not
verifiable, and therefore is not significantly more trustworthy than SNI.

With ESNI, the SNI is encrypted (hence the name). However, the xpectation
is that enterprises which want to do conditional inspection will disable
ESNI on the client. This should not be problematic as they already need
access to the client to install their own trust anchor.

-Ekr



>
> -Tiru
>
>
>
> *From:* Eric Rescorla <ekr@rtfm.com>
> *Sent:* Tuesday, March 12, 2019 3:14 AM
> *To:* Paul Vixie <paul@redbarn.org>
> *Cc:* nalini elkins <nalini.elkins@e-dco.com>om>; Konda, Tirumaleswar Reddy
> <TirumaleswarReddy_Konda@McAfee.com>om>; doh@ietf.org; dnsop@ietf.org;
> Ackermann, Michael <mackermann@bcbsm.com>om>; Christian Huitema <
> huitema@huitema.net>gt;; dns-privacy@ietf.org; Vittorio Bertola
> <vittorio.bertola=40open-xchange.com@dmarc.ietf.org>rg>; Stephen Farrell <
> stephen.farrell@cs.tcd.ie>
> *Subject:* Re: [Doh] [dns-privacy] [DNSOP] New:
> draft-bertola-bcp-doh-clients
>
>
>
> *CAUTION*: External email. Do not click links or open attachments unless
> you recognize the sender and know the content is safe.
> ------------------------------
>
>
>
>
>
> On Mon, Mar 11, 2019 at 11:13 AM Paul Vixie <paul@redbarn.org> wrote:
>
>
>
> nalini elkins wrote on 2019-03-11 10:26:
> > Tiru,
> >
> > Thanks for your comments.
> >
> >  > Enterprise networks are already able to block DoH services,
> i wonder if everyone here knows that TLS 1.3 and encrypted headers is
> going to push a SOCKS agenda onto enterprises that had not previously
> needed one,
>
>
>
> I'm pretty familiar with TLS 1.3, but I don't know what this means. TLS 1.3
>
> doesn't generally encrypt headers any more than TLS 1.2 did, except for
>
> the content type byte, which isn't that useful for inspection anyway.
>
> Are you perchance referring to encrypted SNI? Something else?
>
>
>
> -Ekr
>
>
>
> and that simply blocking every external endpoint known or
> tested to support DoH will be the cheaper alternative, even if that
> makes millions of other endpoints at google, cloudflare, cisco, and ibm
> unreachable as a side effect?
>
> CF has so far only supported DoH on 1.1.1.0/24 and 1.0.1.0/24, which i
> blocked already (before DoH) so that's not a problem. but if google
> decides to support DoH on the same IP addresses and port numbers that
> are used for some API or web service i depend on, that web service is
> going to be either blocked, or forced to go through SOCKS. this will add
> considerable cost to my network policy. (by design.)
>
> --
> P Vixie
>
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