> I wonder if someone studied how unique writing style is.

Since I teach I can tell you that I can usually tell who wrote something by their language and it even works with code. There's also the Enron dataset, which is a common dataset for first time ML students where you do exactly this task.

Your language is in fact a fingerprint. And like you suggest, topics too. Much of our freedom of anonymity comes from the fact that it is hard or not worth it to dox people.

I do agree that verification is a different issue though. I'm not sure keys will solve it because you're not going to sign anything that is scandalous, so it might even give evidence for those that want to falsely claim foul play. And how do you sign a leak?

The problem with signing is that it seems to work for the cases we don't care about and do nothing for the ones we do. That is unless we sign literally everything, including our voice, but then you kill anonymity (why I connected it) and you could then probably clone that too.