[openssl-users] Naive: how to generate EC public key from EC private key?

[Viktor Dukhovni]

> On Mar 17, 2016, at 5:17 PM, Blumenthal, Uri - 0553 - MITLL <uri at ll.mit.edu> wrote:
> 
> I’ve an extremely naïve question. I am generating ephemeral EC keys for ECDH, following the example in https://wiki.openssl.org/index.php/EVP_Key_and_Parameter_Generation
> 
> But it looks like the example ends on generation of the private key:
> /* Generate the key */
> if (!EVP_PKEY_keygen(kctx, &key)) goto err;
> 
> 
> The next step must be obvious, but somehow I can’t figure it out. So my question is: from having EVP_PKEY *privateECKey how do I get EVP_PKEY *publicECKey?

The public key is always there.  You either have both the public and private keys
or just the public key.  So the same EVP_PKEY object holds both.  What you do
next depends on what you want to do with the public key...

-- 
	Viktor.