Encryption is also thousands of years old.

I don't know, but that isn't relevant to this conversation. Slavery was legal for the vast majority of history, but we still all agree today that freedom from slavery is a valid human right. "Due process" itself is a relatively new concept. All human rights were routinely violated for most of history, that's the whole point of enumerating them and discussing them. It's very new that any of these rights are even close to universally accepted.

I can tell you that government surveillance of private communication has at least been a widespread concern for thousands of years. See for example: https://classicalstudies.org/imperial-spies-and-intercepted-....

Many countries have centuries-old constitutional guarantees of the right to secrecy of correspondence: https://www.marottaonmoney.com/right-to-privacy-of-correspon....

Due process? I don't think they bothered with that in the past. Many of the debates about privacy that erupted in the 70s and 80s came because people discovered that the government didn't even bother.