EVP_PKEY_get_int_param is not getting degree from EC key

[Tomas Mraz]

On Tue, 2022-01-04 at 02:33 +0100, Wolf wrote:
> Thank you for the answer!
> 
> On 2022-01-03 10:11:19 +0100, Tomas Mraz wrote:
> > You're using the secp384r1 curve which is a prime field curve. The
> > OSSL_PKEY_PARAM_EC_CHAR2_M parameter can be obtained only for
> > binary
> > field curves.
> > 
> > If you have a group NID for the curve of the EC key, you could use:
> > 
> > EC_GROUP *group = EC_GROUP_new_by_curve_name_ex(NULL, NULL, nid);
> > 
> > to create the group to call EC_GROUP_get_degree() on.
> > 
> > Of course if you can have an EC key with arbitrary explicit group
> > parameters, that would not work.
> 
> That is sadly the case of me.
> 
> > But you can then use number of bits of the OSSL_PKEY_PARAM_EC_P
> > parameter as the degree for prime field curves.
> 
> So, I've tried following your advice, but for some reason it is still
> failing for me. I've modified my example program to be:

You need to use EVP_PKEY_get_bn_param() to get the P parameter and
BN_num_bits() to count the number of bits of the P value.


-- 
Tomáš Mráz, OpenSSL