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Re: [TLS] AD review of draft-ietf-tls-negotiated-ff-dhe-08

mrex@sap.com (Martin Rex) Wed, 01 April 2015 04:27 UTC

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To: Martin Thomson <martin.thomson@gmail.com>
Date: Wed, 01 Apr 2015 06:27:31 +0200
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From: mrex@sap.com
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Subject: Re: [TLS] AD review of draft-ietf-tls-negotiated-ff-dhe-08
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Martin Thomson wrote:
> Stephen Farrell <stephen.farrell@cs.tcd.ie> wrote:
>>
>> #1 Have we tested in the wild that using elliptic_curves (10)
>> in the ClientHello won't trigger some ECC code that causes
>> handshakes to barf?
> 
> Firefox sends the supported_curves extension in every handshake and so
> do most browsers.  So for those, the risk of intolerance is obviously
> quite low.  That's not hard numbers obviously, but that's a lot of
> ClientHello messages with the extension.

I think Stephen might have meant something else.

RFC4492 contains the following explicit prohibition (Section 4, 4th paragr.):

   https://tools.ietf.org/html/rfc4492#section-4


   The client MUST NOT include these extensions in the ClientHello
   message if it does not propose any ECC cipher suites. 


and the above requirement seems to prohibit a non-ECC client from
using the named FFDHE parameters through the ECC named curve extension
_without_ accompanying ECC cipher suites.


-Martin

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