Re: [TLS] DNS-based Encrypted SNI

Eric Rescorla <ekr@rtfm.com> Wed, 04 July 2018 16:54 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Wed, 4 Jul 2018 09:53:30 -0700
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To: Ilari Liusvaara <ilariliusvaara@welho.com>
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Subject: Re: [TLS] DNS-based Encrypted SNI
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On Wed, Jul 4, 2018 at 6:08 AM, Ilari Liusvaara <ilariliusvaara@welho.com>;
wrote:

> On Wed, Jul 04, 2018 at 05:56:07AM -0700, Eric Rescorla wrote:
> > On Tue, Jul 3, 2018 at 9:48 PM, Ilari Liusvaara <
> ilariliusvaara@welho.com>;
> > wrote:
> >
> > > On Mon, Jul 02, 2018 at 04:39:14PM -0700, Eric Rescorla wrote:=
> > > > I am working on an implementation for NSS/Firefox and I know some
> > > > others are working on their own implementations, so hopefully we can
> > > > do some interop in Montreal.
> > > >
> > > > This is at a pretty early stage, so comments, questions, defect
> > > > reports welcome.
> > >
> > > One thing I noticed: First there is this in evaluation:
> > >
> > > 7.2.4.  Do not stick out
> > >
> > >    By sending SNI and ESNI values (with illegitimate digests), or by
> > >    sending legitimate ESNI values for and "fake" SNI values, clients do
> > >    not display clear signals of ESNI intent to passive eavesdroppers.
> > >
> > > Is that suggesting to send fake ESNI values? If so, there is this in
> > > endpoint behavior:
> > >
> >
> > No, you would not send fake ESNI values. The idea here is that there is a
> > group of IPs (associated with a big provider, then all ESNI-supporting
> > clients will send ESNI to it. So the provider will stick out, but the use
> > of site X versus site Y on the provider will not    stick out. And the
> > provider's IPs are reasonably well known through other mechanisms, so
> this
> > doesn't tell you much. Of course, this does not help big sites that
> aren't
> > using shared infrastructure (e.g., Facebook), but I don't know how to do
> > that.
>
> What does "with illegitimate digests" mean then?
>

I didn't write this text, but I agree that it's in conflict with the
requirement that
you abort with an unknown key. We went through some design variants and
this looks like a remnant of a previous one.

-Ekr


>
> -Ilari
>