Lets take an old idea and reuse it – now to induce a disadvantage to those with huge amounts of specifically electronic eavesdropping and reporting capability. Lets use the 3d printer to make coded paper (codes are built into the fabric) upon which innocuous writing may be written, and which may be transmitted by royal mail. One should assume the envelope is photographed in sequence with others in its sorting order “locality” (at re-sorting stations) aswell as being routed by the imprinted code assigned to the envelope at the submission office.
Lets say one receives such a thing and one has to authenticate it, since it may be a key list. Since its fabricated using commodity printers, of course counter espionage/subversion types can just as easily make the things (and perform a substitution).
So what we want is design output that takes longer to read, decode and cryptanalyze (and essentially then reproduce into a new bearer substrate the spoofed keylist) than it takes to overnight deliver the envelope. After all, if it doesn’t arrive on schedule (sampling the variance of arrival time for n letters sent), one knows the game is up. It must cost real money and real HUMAN time each run (whereas sending a letter each day must cost 50c) so that spying itself hurts, causing economic damage through cost escalation (for very little reward).
Of course the argument here is little more than exploitation of asymmetric advantage, repurposing civil infrastructure.