xor_derive
static OSSL_FUNC_keyexch_derive_fn xor_derive;
{ OSSL_FUNC_KEYEXCH_DERIVE, (void (*)(void))xor_derive },
|| !xor_derive(derivectx, ss, sslen, XOR_KEY_SIZE))
|| !xor_derive(derivectx, ss, sslen, XOR_KEY_SIZE))