Re: [TLS] Curve25519 in TLS

Simon Josefsson <simon@josefsson.org> Thu, 12 September 2013 20:42 UTC

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From: Simon Josefsson <simon@josefsson.org>
Date: Thu, 12 Sep 2013 13:41:56 -0700
To: Rob Stradling <rob.stradling@comodo.com>, Yoav Nir <ynir@checkpoint.com>
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Cc: Patrick Pelletier <code@funwithsoftware.org>, "tls@ietf.org" <tls@ietf.org>
Subject: Re: [TLS] Curve25519 in TLS
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Rob Stradling <rob.stradling@comodo.com>; skrev:
>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?

For performance reasons?  It is more efficient.

/Simon
>
>> 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