In Vernor Vinge&#x27;s <i>A Fire Upon the Deep</i> I recall a plot element along these lines. Traders traffic in cubes of material that acts as a super dense source of pad data. Your communication partner on another ship would have the twin cube, and the two would be synced up and then provide the carrier data stream for video and other content. When your cubestuff is exhausted your secure authenticated comms cease.