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Re: [Cfrg] MAY use specified curves

Manuel Pégourié-Gonnard <mpg@elzevir.fr> Tue, 09 September 2014 18:59 UTC

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Date: Tue, 09 Sep 2014 20:59:09 +0200
From: Manuel Pégourié-Gonnard <mpg@elzevir.fr>
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To: Stephen Farrell <stephen.farrell@cs.tcd.ie>, Dan Brown <dbrown@certicom.com>, "cfrg@irtf.org" <cfrg@irtf.org>
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Subject: Re: [Cfrg] MAY use specified curves
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On 09/09/2014 20:36, Stephen Farrell wrote:
> On 09/09/14 18:03, Dan Brown wrote:
>>
>> My understanding is that many IETF WGs have applied a MUST NOT to the
>> ANSI/SECG mechanisms of specifying an elliptic curve.  
> 
> I'm not clear what you mean here. Can you provide citations?
> 
I can't say for sure what Dan was referring to, but there is a MUST NOT in PKIX,
specifically RFC 5480 section 2.1.1:

     ECParameters ::= CHOICE {
       namedCurve         OBJECT IDENTIFIER
       -- implicitCurve   NULL
       -- specifiedCurve  SpecifiedECDomain
     }
       -- implicitCurve and specifiedCurve MUST NOT be used in PKIX.
       -- Details for SpecifiedECDomain can be found in [X9.62].
       -- Any future additions to this CHOICE should be coordinated
       -- with ANSI X9.

On the other hand, TLS allows specified curves, via the special NamedCurve
values arbitrary_explicit_prime_curves and  arbitrary_explicit_char2_curves (RFC
4492 section 5.1.1). But according to wikipedia [1], none of the usual TLS
libraries implement this option.

[1]
https://en.wikipedia.org/wiki/Comparison_of_TLS_implementations#Supported_elliptic_curves

(Outside of PKIX and TLS, I have no idea.)

Manuel.

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