code: func (k SecretKey) Box(receiver saltpack.BoxPublicKey, nonce saltpack.Nonce, msg []byte) []byte {
  	ret := box.Seal([]byte{}, msg, (*[24]byte)(&nonce), (*[32]byte)(receiver.ToRawBoxKeyPointer()), (*[32]byte)(&k.sec))
  	return ret
  }
docs: // Box runs the NaCl box for the given sender and receiver key.