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

Peter Gutmann <> Tue, 26 July 2016 07:48 UTC

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From: Peter Gutmann <>
To: Ilari Liusvaara <>, Martin Rex <>
Thread-Topic: [TLS] weird ECDSA interop problem with cloudflare/nginx
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Date: Tue, 26 Jul 2016 07:48:05 +0000
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Subject: Re: [TLS] weird ECDSA interop problem with cloudflare/nginx
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Ilari Liusvaara <> writes:

>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).

Do you have any more details on some of the issues you ran into?  It'd be good
to know for anyone else in this situation.

(I've had to do the same thing, with awkward logic that backs off and retries
different options if an earlier attempt fails.  This was one of the motivators
for the Grigg's Law cipher-suite handling in TLS-LTS).