I think "entitled to every man's evidence" means that there is a compulsory subpoena power to make people testify. One can call a hostile witness, and in the absence of a corresponding privilege against testifying, the witness can be punished for refusing to testify, as a contemnor (or for testifying falsely, as a perjuror).

This idea is distinct from search and covert eavesdropping powers, which may have also existed at common law but perhaps not under that same principle?

Yeah, I don't think the public claim to every person's evidence vindicates dragnet surveillance! I think these are complicated issues, we can make our own policy decisions and we can find a right to privacy even if one didn't exist at the time of the founders.

I'm just reacting to the notion that we've departed from the principles of the founders by giving law enforcement access to evidence. My impression, from the bit of reading I've done, is that wouldn't have shocked the conscience of the founders at all.

I'm not sure how you mean to apply that idea. If you mean that it balances the right of privacy, that seems like a stretch to apply to encryption. My evidence might be in my head, for example. Nothing stops me from burning records unless they already are potential evidence in an active case. I could delete this comment.