It's pretty easy to find with a google search, but I'm referencing the "classic" tools of spycraft. Hand-written messages that actually self-destruct (self-immo

It's pretty easy to find with a google search, but I'm referencing the "classic" tools of spycraft. Hand-written messages that actually self-destruct (self-immolate), invisible ink, short-wave radio, burst transmissions, leaving physical messages at dead-drops. While steganography usually refers to the practice of concealing a file, message, image, or video within another file, message, image, or video, it can be extended to the practice of hiding information in plain sight. An example is encoding a message into what passes for street graffitti. Or laying out rocks in a formation that only a drone or satellite can make sense of. One of the smartest people I've ever met explained to me that more or less all digital communications are compromised if the resources of a nation-state are aligned against you and that the only practical solution for private and secure messages is hiding information in plain sight.