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

Ilari Liusvaara <ilariliusvaara@welho.com> Mon, 25 July 2016 19:37 UTC

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Date: Mon, 25 Jul 2016 22:37:08 +0300
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: Martin Rex <mrex@sap.com>
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Subject: Re: [TLS] weird ECDSA interop problem with cloudflare/nginx
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On Mon, Jul 25, 2016 at 09:08:49PM +0200, Martin Rex wrote:
> I've just run into a weird interoperability problem with an (alleged)
> cloudflare/nginx TLS server and my personal Firefox settings.
> 
> https://regmedia.co.uk/2015/07/14/giant_weta_mike_locke_flicker_cc_20.jpg
> 
> 
> Traditionally I have all TLS ciphersuites with ECDSA disabled through
> about:config, but it seems that recently two new TLS ciphersuites were
> added to FF, which caused complete loss of interop with regmedia.co.uk
> for me with my existing configuration. (Loss of pictures&media on the
> www.theregister.co.uk news site).
> 
> It looks like a bug in the cloudflare/nginx cipher suites selection
> algorithm, which appears to blindly go for ECDSA, even though there is
> no actual ECDSA cipher suite available which the server supports.

I recently (tried to) implement(ed) TLS 1.2 ciphersuite negotiation
in a way that always negotiates something if at least one valid
configuration exists, and respects TLS 1.2 rules.

The resulting code was totally insane, and I am very much not surprised
to see buggy implementations. Nor can I say my implementation is not
buggy, as testing that mess is just about impossible (and it it will
very much do GIGO in order to maximize interop).


-Ilari