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Re: [TLS] Should we require implementations to send alerts?

Nico Williams <nico@cryptonector.com> Thu, 17 September 2015 21:52 UTC

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Date: Thu, 17 Sep 2015 16:52:32 -0500
From: Nico Williams <nico@cryptonector.com>
To: Brian Smith <brian@briansmith.org>
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Subject: Re: [TLS] Should we require implementations to send alerts?
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On Thu, Sep 17, 2015 at 02:46:39PM -0700, Brian Smith wrote:
> On Thu, Sep 17, 2015 at 1:50 PM, Nico Williams <nico@cryptonector.com>
> wrote:
> > Do we think that silent connection closings wouldn't also lead to
> > version fallback?
> 
> Let's ask the browser vendors:
> 
> Browser vendors, if web servers were to stop sending alerts during
> handshake failures, would you start doing version fallback when a
> connection is closed?

That's not how we answers to questions like that.  These behaviors (on
the part of developers) arise long after we think ask the question.

The point is: if they did it then, why would we think they wouldn't do
it now without fatal alerts?

Spoiler alert!1!!: developers want the user experience to be smooth,
security be damned, so yes, they will in fact implement version
fallbacks on connection close.

But now consider a fatal alert that conveys a "it's not gonna work with
earlier versions either, you dummy" message.  That's got a slightly
better chance of working.

Nico
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