If the framers had meant to say "provide evidence" instead of "be a witness" they would have said that. They were lawyers and those words were commonly used legal terms that meant the same things they do today.

"To bear arms" doesn't mean to have human arms, after all

If the government can't compel someone to say when, where and how they disposed of the bodies, then they also can't make someone explain how they encrypted some files.

In case they can confirm the existence of files some other way I guess you could make the case that the government can force someone to produce those files. Of course this won't tell them anything they didn't know already (which is kind of the point). Making someone produce files that may or may not exist is the same as making them testify that those files exist and that they have access to them, which I would argue falls under the 5th amendment.

The Fifth Amendment has been consistently interpreted to mean far more than "confession"

?!