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Re: [TLS] Ensuring consistent strength across certificate, ECDHE, cipher, and MAC

Peter Gutmann <pgut001@cs.auckland.ac.nz> Thu, 24 March 2016 12:23 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: Hubert Kario <hkario@redhat.com>, "tls@ietf.org" <tls@ietf.org>
Thread-Topic: [TLS] Ensuring consistent strength across certificate, ECDHE, cipher, and MAC
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Date: Thu, 24 Mar 2016 12:22:56 +0000
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Subject: Re: [TLS] Ensuring consistent strength across certificate, ECDHE, cipher, and MAC
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Hubert Kario <hkario@redhat.com> writes:

>In my experience, many (12%) servers simply ignore the list of curves
>advertised by client and use the P-256 curve always.
>
>Some (58%) check if it was advertised and fallback to non-ECDHE if P-256 is
>not advertised.

When I checked, which is a year or two back now, I found similar problems (I
didn't get hard figures but I had the feeling it was a lot higher than 12%,
but then I wasn't conducting a rigorous survey).  Conversely, I found that if
you just ploughed ahead with P-256, things usually worked.  This is what
motivated the use of P-256 in -LTS, it's the de facto standard curve.

Peter.

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