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

mrex@sap.com (Martin Rex) Tue, 26 July 2016 09:52 UTC

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From: mrex@sap.com (Martin Rex)
Archived-At: <https://mailarchive.ietf.org/arch/msg/tls/xFhLgWiQPBdVNBQFmEYYoKV--ig>
Subject: Re: [TLS] weird ECDSA interop problem with cloudflare/nginx
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Viktor Dukhovni wrote:
> 
>> On Jul 25, 2016, at 3:08 PM, Martin Rex <mrex@sap.com> wrote:
>> 
>> specifically, after the FF update, this new TLS ciphersuite:
>> 
>>   security.ssl3.ecdhe_ecdsa_aes_128_gcm_sha256  (0xcc, 0xa9)
>> 
>> was the only ECDSA cipher suite enabled in my Firefox 47.0.1, and this
>> kills connectivity (TLS handshake_failure alert) with regmedia.co.uk.
> 
> OpenSSL lists "CC, A9" as:
> 
> 0xCC,0xA9 - ECDHE-ECDSA-CHACHA20-POLY1305 TLSv1.2 Kx=ECDH     Au=ECDSA Enc=CHACHA20/POLY1305(256) Mac=AEAD
> 
> Which is not AES_128_GCM.  The IANA registry seems to agree:
> 
> https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#tls-parameters-4
> 
>   0xCC,0xA9	TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256	Y	[RFC7905]


Sorry for the confusion about the cipher suite.

The issue seems a little weirder than what I thought, because the
failure seems to happen only for a particular cipher suite combo
(which happens to be the combo produced by my own Firefox config):

I can repro the handshake failure with openssl-1.1.0-pre5 with this
command line:

Failure:
openssl s_client -connect regmedia.co.uk:443 -cipher ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-CHACHA20-POLY1305

Success:
openssl s_client -connect regmedia.co.uk:443 -cipher ECDHE-RSA-AES128-GCM-SHA256

Success:
openssl s_client -connect regmedia.co.uk:443 -cipher ECDHE-ECDSA-CHACHA20-POLY1305



-Martin