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

[Hubert Kario <[e-mail]>]

On Tuesday, 26 July 2016 12:08:33 CEST 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.
> 
> > 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.

if you send the AES-GCM then Chacha but do NOT include signature algorithms, 
it allows you to connect (other extensions are irrelevant).

If you send AES-GCM then Chacha in ciphers but in signatures algorithms don't 
include the SHA256/ecdsa pair, it works too.

in other words, this connects:
openssl s_client -connect regmedia.co.uk:443 -cipher ECDHE-RSA-AES128-GCM-
SHA256:ECDHE-ECDSA-CHACHA20-POLY1305 -sigalgs ECDSA+SHA512:RSA+SHA256

and this connects:
openssl s_client -connect regmedia.co.uk:443 -cipher ECDHE-RSA-AES128-GCM-
SHA256:ECDHE-ECDSA-CHACHA20-POLY1305 -sigalgs ECDSA+SHA512:RSA+SHA512

but this doesn't:
openssl s_client -connect regmedia.co.uk:443 -cipher ECDHE-RSA-AES128-GCM-
SHA256:ECDHE-ECDSA-CHACHA20-POLY1305 -sigalgs ECDSA+SHA256:RSA+SHA256

(using openssl-1.1.0-pre5)
-- 
Regards,
Hubert Kario
Senior Quality Engineer, QE BaseOS Security team
Web: www.cz.redhat.com
Red Hat Czech s.r.o., Purkyňova 99/71, 612 45, Brno, Czech Republic