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Re: [TLS] I-D Action: draft-ietf-tls-negotiated-ff-dhe-02.txt

Henrick Hellström <henrick@streamsec.se> Sat, 25 October 2014 18:06 UTC

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Date: Sat, 25 Oct 2014 20:06:02 +0200
From: Henrick Hellström <henrick@streamsec.se>
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To: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>
References: <20141011044948.27553.93984.idtracker@ietfa.amsl.com> <5438B82B.6090600@fifthhorseman.net> <544BD3BF.9030702@streamsec.se> <20141025172504.GA2714@LK-Perkele-VII>
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Subject: Re: [TLS] I-D Action: draft-ietf-tls-negotiated-ff-dhe-02.txt
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On 2014-10-25 19:25, Ilari Liusvaara wrote:
> I see two problematic cases:
> 1) NG SKE gets presented as EC(!) SKE.
> 2) NG SKE gets presented to non-NG client.
>
>
> 1) The message is:
>
> 00 02 01 xx 00 01 00 <length of ge> <ge>
>
> When interpretted as elliptic curve, this has curve type of 0, which is
> not valid, so handshake can't work.

I think this should be of no consequence. A client that interprets a DHE 
SKE as an ECDHE SKE, despite having negotiated a DHE cipher suite, is 
broken beyond repair and would be pointless to try to be compatible with.

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