My uncle was a career NSA man. In the 1970s, his job (I learned decades later) was to modify and maintain all the typewriters in the White House so their keystrokes couldn't be used to identify what was being typed on them. Presumably the concern was that something like a Buran eavesdropping system could be used to detect vibrations in windows, and the sound of the typewriter keys then extracted and analyzed to recover the text.
My grandfather (also career NSA) used to tell me that it would seem like fiction if people knew some of the things that technology and a good cryptanalyst could do. I think he was right.
"his job (I learned decades later) was to modify and maintain all the typewriters in the White House so their keystrokes couldn't be used to identify what was being typed on them."
How would you do that? Soundproofing? Delay on the mechanical action? What is the fingerprint that allows transcription of a sound sample?
If I was given this job, not knowing anything about typewriters or spying, my first plan would be to modify all typewriters regularly by switching parts around according to a random draw, and also by rejigging any calibration settings (individual letter height, etc). This would modify both the sound of the typewriters and the fingerprints of the actual typed output [1].
This way, there would never be a per-typewriter profile, because all machines are randomised every week. Obviously, I'd also have a white-room analysis team checking whether the scheme works.
Maybe someone who knows more about typewriters could tell me whether this would work at all, or there is a fatal flaw.
My grandfather (also career NSA) used to tell me that it would seem like fiction if people knew some of the things that technology and a good cryptanalyst could do. I think he was right.