Advancements in information warfare have exposed every form of electronic communication to jamming or interception, while the breaking of P versus NP has rendered encryption a thing of the past. Imitative AI means that even a face or voice on the other end of a connection can no longer be trusted as genuine.

To transmit messages of a confidential nature, there has been a return to physical media. SUB missives are one of the few guarantees of privacy left, and are now used extensively by the military, in politics and spying, and by the many megacorporations seeking to avoid corporate espionage.

SUB missives are vat-grown bodies typically built for speed and self-defense, and rigged to self-destruct should any tampering be detected. Often they are uploaded with a copy of the person sending the message (the one person that they know they can truly trust) or a subordinate. They may then either memorize the message or physically courier it to the recipient, or the details may be encoded into their mental engrams during the upload, such that they themselves are unaware of its details.

Upon delivery, the recipient may wipe or otherwise dispose of the SUB, or return them to sender with the reply.