Secure communication based on message encryption might be performed by combining the message with
controlled noise (called pseudo-noise) as performed in spread-spectrum communication used presently
in Wi-Fi and smartphone telecommunication systems. Quantum communication based on entanglement is
another route for securing communications as demonstrated by several important experiments described
in this work. The central role played by the photon in unifying the description of classical and
quantum noise as major ingredients of secure communication systems is highlighted and described on
the basis of the classical and quantum fluctuation dissipation theorems.