I don't think that's necessarily the case. It seems like you could have a
bare public key:
{
"kty": "EC",
"crv": "P-256",
"d": "..."
}
You can compute the public key from that information, since the base point
for the cyclic group is specified as part of the definition of P-256 [1].
Namely, if G is the base point, you just compute d*G. That's arguably
even more trivial than computing an RSA public key from the private key.
(EC point multiplication vs. Euclidean algorithm. At least it uses the
same operation as ECDH.)
[1] <http://csrc.nist.gov/publications/fips/fips186-3/fips_186-3.pdf>
On Fri, May 24, 2013 at 9:07 AM, Richer, Justin P. <[email protected]>wrote:
> It was my read of the spec that the private key components are always in
> addition and the resulting object is a key pair.
>
> -- Justin
>
> On May 24, 2013, at 7:22 AM, Ludwig Seitz <[email protected]> wrote:
>
> > Hello,
> >
> > while implementing the JWK EC part of the JOSE draft, I've come across
> > the following question:
> >
> > draft-ietf-jose-json-web-algorithms-10
> >
> > "5.2.2. JWK Parameters for Elliptic Curve Private Keys
> >
> > In addition to the members used to represent Elliptic Curve public
> > keys, the following member MUST be present to represent Elliptic
> > Curve private keys:"
> >
> > However an EC private key is fundamentally different from an EC public
> > key, it is just an integer and doesn't have the x and y
> > parameters that an EC public key has. So when representing a EC private
> > key, the x and y members of the public key are not
> > readily available.
> >
> > Was it the intention of the WG that the encoding of the EC private key
> > should include the parameters from the public key?
> >
> >
> > Regards,
> >
> > Ludwig Seitz
> > --
> > Ludwig Seitz, PhD
> > SICS Swedish ICT AB
> > Ideon Science Park
> > Building Beta 2
> > Scheelevägen 17
> > SE-223 70 Lund
> >
> > Phone +46(0)70-349 92 51
> > http://www.sics.se
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> > https://www.ietf.org/mailman/listinfo/jose
>
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