# [Cryptography-dev] ECPrivateKey form private_value

Paul Kehrer paul.l.kehrer at gmail.com
Sat May 16 06:23:33 CEST 2015

```Help is always appreciated; if you'd like to submit a PR we'll be happy to review it!

-Paul

On May 15, 2015 at 3:26:29 PM, Dario Sneidermanis (dariosn at gmail.com) wrote:

That'd be perfect. If you need a hand I can make a first draft over the weekend.

Dario

On Thu, May 14, 2015 at 2:45 PM, Alex Gaynor <alex.gaynor at gmail.com> wrote:
Perhaps an EllipticCurvePrivateNumbers.from_private_number_and_curve() would be appropriate to automatically compute the public key?

Alex

On Thu, May 14, 2015 at 12:11 PM, Paul Kehrer <paul.l.kehrer at gmail.com> wrote:
Hi Dario,

The creation of an EllipticCurvePrivateNumbers object does require you to do d*G yourself at this time. There is some precedent for us adding functions to compute other elements (see: https://cryptography.io/en/latest/hazmat/primitives/asymmetric/rsa/#handling-partial-rsa-private-keys) so a function to do this makes sense to me.

-Paul

On May 14, 2015 at 3:21:29 AM, Dario Sneidermanis (dariosn at gmail.com) wrote:

Hi,

I'm trying to compute an EllipticCurvePrivateKey from a private_value (d). It seems that the only way to achieve this is to create an EllipticCurvePrivateNumbers object, but the constructor takes both the private_value and the public_numbers.

Why does it need the public_numbers, when it could compute them (knowing the curve), by doing d*G (G being the curve generator)?

Is there any way to go from d to the ECPrivKey without doing d*G by myself?

Thanks,
Dario
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