Re: [TLS] weird ECDSA interop problem with cloudflare/nginx

Ilari Liusvaara <ilariliusvaara@welho.com> Tue, 26 July 2016 14:35 UTC

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Date: Tue, 26 Jul 2016 17:09:06 +0300
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: tls@ietf.org
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Subject: Re: [TLS] weird ECDSA interop problem with cloudflare/nginx
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On Tue, Jul 26, 2016 at 12:08:33PM +0000, Viktor Dukhovni wrote:
> On Tue, Jul 26, 2016 at 01:09:04PM +0300, Ilari Liusvaara wrote:
> 
> > > Failure:
> > > openssl s_client -connect regmedia.co.uk:443 -cipher ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-CHACHA20-POLY1305
> > 
> > If you swap the order of these two ciphersuites, does it suceed or fail?
> > 
> > I.e.
> > 
> > openssl s_client -connect regmedia.co.uk:443 -cipher ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-AES128-GCM-SHA256
> 
> I can reproduce the reported failure in the original order, and at
> least for me the swapped variant succeeds.

Thank you.
 
> > Well, your test results certainly blow basic "negotiation accidentially
> > blows off all valid candidates and then fails" hypothesis out of the
> > water. So it has to be soemthing more complicated.
> > 
> > Succeeding with the ciphersuites swapped would suggest (as somebody
> > else in this thread already said) that it only considers Chacha in
> > the first place, not noticing that it may be the only choice after
> > certificate selection.
> 
> Perhaps that's the issue.

Oops, that should have been:

Chacha ciphersuites are considered for certificate selection in any
position, but only in first position for protection selection.


-Ilari