in source/ec_override.c [374:377]
bool ec_key_is_valid(EC_KEY *key) {
return key && (0 < key->references) && ec_group_is_valid(key->group) && (key->group->asn1_form == key->conv_form) &&
key->pub_key_is_set && (!key->priv_key || bignum_is_valid(key->priv_key));
}