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Comment by keithpeter | Hacker News Reader

"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?

https://www.freesound.org/people/keithpeter/sounds/123344/

have at it...

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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.

[1] http://scholar.google.com.au/scholar?q=%22typewriter+identif...

> How would you do that? Soundproofing? Delay on the mechanical action? What is the fingerprint that allows transcription of a sound sample?

Perhaps you could modify key levers in such a fashion that each stroke requires variable pressure?

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