x25519_448_core
ret = x25519_448_core(priv_key, u, pub_key, len);
ret = x25519_448_core(priv_key, u, pub_key, len);
ret = x25519_448_core(priv_key, peer_pub_key, shared_secret, len);
return x25519_448_core(k, u, res, X25519_SIZE);
return x25519_448_core(k, u, res, X448_SIZE);