In the Morse Code era, the phrase “fist” referred to the unique style that every telegraph operator brought to their communications. The phrase “recognized the fist” comes up again and again in various wartime and spy literature; it refers to hearing someone tapping out Morse Code and being able to distinguish the operator by their style. This was far from a trivial detail of the telegraph era; in more than one case lives were saved (or lost) because someone was able to differentiate between who an operator was supposed to be and who they actually were.
Fast-forward a hundred years, and it’s now possible to spy on what someone is typing by leaving a phone on their desk and having it pick up the vibrations from the physical activity of typing. (A laser mike pointed at your window works equally well, unfortunately.) Your typing style is like a fingerprint. It doesn’t even take a high-power microprocessor to determine what you’re doing on a computer. My first wife claimed to be able to tell, from a distance of across our house, whether I was programming, writing for a website, engaging in an Instant Messenger chat, or arguing with someone online on my old IBM Model M mechanical keyboard. Well, I shouldn’t say “claimed.” More like she just plain knew. Her accuracy rate was effectively 100%. Never once did she accuse me of not working when I was working, or vice versa.
Incidentally, this idea of being able to identify patterns in communications behavior is also how most cryptography is undone. There’s a brilliant scene in the novel Cryptonomicon where a highly complex cipher is broken because a cipher clerk doesn’t always close her eyes when she reaches into a bowl full of wooden balls — and although that scene is written right at the edge of the reader’s credulity, it has mathematical basis in fact. The whole difference between “128-bit” and “2048-bit” encryption is how effective the method is in reducing the “fist” or “fingerprint” of a conversation.
I do believe that tale of the first Mrs Baruth; I bang on a Model M to this day, and what it sounded like when I wrote this paragraph is nothing like what it sounded like when I recapped the Thunder-Spurs game. I don’t think anyone is listening — why would they care? — but I have learned not to be surprised.