ecccdh_derive_secret
ATTRIBUTE_WARN_UNUSED_RET int ecccdh_derive_secret(const ec_priv_key *our_priv_key, const u8 *peer_pub_key, u8 peer_pub_key_len, u8 *shared_secret, u8 shared_secret_len);
ret = ecccdh_derive_secret(&(kp.priv_key), c->peer_pub_key, c->peer_pub_key_len, shared_secret, shared_secret_len);
ret = ecccdh_derive_secret(&priv_key, serialized_pub_key, serialized_pub_key_size, sharedsecret_check, sharedsecretsize);