Re: [TLS] Update on TLS 1.3 Middlebox Issues

Eric Rescorla <ekr@rtfm.com> Sat, 07 October 2017 14:08 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Sat, 7 Oct 2017 07:08:01 -0700
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To: Ilari Liusvaara <ilariliusvaara@welho.com>
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Subject: Re: [TLS] Update on TLS 1.3 Middlebox Issues
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On Sat, Oct 7, 2017 at 2:57 AM, Ilari Liusvaara <ilariliusvaara@welho.com>;
wrote:

> On Fri, Oct 06, 2017 at 01:16:37PM -0700, Eric Rescorla wrote:
> > Hi folks,
> >
> > In Prague I mentioned that we were seeing evidence of increased
> > failures with TLS 1.3 which we believed were due to middleboxes. In
> > the meantime, several of us have done experiments on this, and I
> > wanted to provide an update.
> >
> > The high-order bit is that *negotiating* TLS 1.3 seems to cause
> > increased failures with a variety of middleboxes (it’s generally safe
> > to offer TLS 1.3 to servers which don’t support it). The measured
> > incremental error rates vary quite a bit, ranging from minimal
> > (Facebook) to ~1.5% (Firefox) and ~3.4% (Chrome). Each of us is using
> > a slightly different methodology (organic versus forced traffic) and
> > different populations (mobile, desktop, enterprise, etc), but it does
> > seem like there is a nontrivial failure rate. At this point, we have
> > two options:
> >
> > - Fall back to TLS 1.2 (as we have unfortunately done for previous
> releases)
> > - Try to make small adaptations to TLS 1.3 to make it work better with
> > middleboxes.
>
> What you think is acceptable failure rate? That is, if we can't get
> the rate below that, don't bother with adaptation?
>

I'm not precisely sure. I think it would depend on the client profile, but
at this existing rate, Firefox, at least, would have to do fallback. That's
what Firefox Beta currently does.


> > The Chrome team has been working on angle #2 and has been having
> > success with an approach of trying to make TLS 1.3 connections look
> > more like TLS 1.2. Their current experiments get them down to about 1%
> > incremental failures and they are currently measuring some changes
> > they hope will shave that down more. These changes are a bit annoying
> > but basically superficial; they do not affect the cryptography.
> >
> > Separately, Firefox and Facebook have been experimenting with the new
> > content type described in PR#1051 (Google’s and Facebook’s results
> > conflict, so this is a bit of a mystery). We hope to have results from
> > both sets of experiments by end of October, at which point we should
> > be able to discuss the best way forward as a group.
>
> Has there been attempts at figuring out what exactly the middleboxes
> are intolerant to?


Yes, there has been some of that, but mostly by the Google team and I don't
want to speak for them.

Best,
-Ekr