x25519_derive_secret
ATTRIBUTE_WARN_UNUSED_RET int x25519_derive_secret(const u8 priv_key[X25519_SIZE], const u8 peer_pub_key[X25519_SIZE], u8 shared_secret[X25519_SIZE]);
ret = x25519_derive_secret(c->our_priv_key, c->peer_pub_key, shared_secret);
ret = x25519_derive_secret(t->privkey, t->peerpubkey, sharedsecret_check);