Re: [TLS] Curve25519 in TLS

Rob Stradling <rob.stradling@comodo.com> Thu, 12 September 2013 19:04 UTC

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Date: Thu, 12 Sep 2013 20:04:25 +0100
From: Rob Stradling <rob.stradling@comodo.com>
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To: Yoav Nir <ynir@checkpoint.com>
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Cc: Simon Josefsson <simon@josefsson.org>, Patrick Pelletier <code@funwithsoftware.org>, "tls@ietf.org" <tls@ietf.org>
Subject: Re: [TLS] Curve25519 in TLS
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On 12/09/13 14:58, Yoav Nir wrote:
> On Sep 12, 2013, at 3:51 PM, Rob Stradling <rob.stradling@comodo.com> wrote:
>> On 11/09/13 18:12, Simon Josefsson wrote:
<snip>
>>> Yes perhaps.  What would the purpose of using Curve25519 in X.509
>>> certificates be?
>>
>> I just thought it seemed like a logical thing to do.  We can already do ECDHE-ECDSA using the NIST curves for both keys in certs and for key exchange, so why wouldn't we allow Curve25519 to be used for both purposes?
>>
>> Unless NIST can prove that their curves aren't backdoored, I think it's likely that some folks (rightly or wrongly) will want to do ECDHE-ECDSA without touching the NIST curves at all.  What options do they have?
>
> Umm, the brainpool curves are available.

Yes, and the brainpool curves are also available for key exchange.

So why bother making curve25519 available for key exchange?

> Also, I don't get why performance would be less critical than that of ECDHE. In a full handshake, you do both an ECDSA signature and the ECDHE operations. Why would one matter while the other does not?

+1

-- 
Rob Stradling
Senior Research & Development Scientist
COMODO - Creating Trust Online