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Re: Question about ECDH

From: Charles Engelke <w3c@engelke.com>
Date: Tue, 19 Jul 2016 16:59:10 -0400
Message-ID: <CAFeVzdw3Toig08tuxk_-1=98mS2cOnM_0yRTMihDQkGDEphErA@mail.gmail.com>
To: Mark Watson <watsonm@netflix.com>
Cc: Charles Engelke <w3c@engelke.com>, "public-webcrypto@w3.org" <public-webcrypto@w3.org>
On Tue, Jul 19, 2016 at 4:46 PM, Mark Watson <watsonm@netflix.com> wrote:

> Hi Charles,
> Thanks - that explanation makes sense: there are two ways to do ECDH
> defined in SEC1, the RFC uses one of them and X9.62 uses the other and they
> are the same for curves with cofactor 1.
> So, then, can anyone tell me what is the co-factor of the curves we
> defined in the WebCrypto specification ? If that is 1, then I am convinced
> that the RFC and X9.62 are the same and we can safely switch.

SEC 2: Recommended Elliptic Curve Domain Parameters (
http://www.secg.org/SEC2-Ver-1.0.pdf) defines secp256r1, secp384r1, and
secp521r1, which are alternate names for P-256, P-384, and P-521. According
to this PDF, all three curves have cofactor h=1.
Received on Tuesday, 19 July 2016 20:59:39 UTC

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