And what they say in the industries that need to take this ultra seriously (Banking and Insurance companies, for example) an untested backup is not considered a good backup. And the only way to truly test a backup is install a fresh image of the entire OS (using checksums on the image too), so that you can read the data and make sure no clever ransome-ware software is secretly encrypting EVEN your backups.

oh, btw. "Blockchains solve this" haha.

Well, yeah.. you never want to test backups on the same computer you made them, so to test them, you should go to secondary/friends/work computer and try to access the files. Boot from a fresh LiveUSB stick if you are feeling paranoid. At least once you have backup configured, there is often a fuse driver, so an easy way to do so is to browse backups and try to open a few documents at random.

As for "encrypting your backups", that's what the "check" command is for - it can't ensure that this .py file actually contains python code (and not encrypted data with ransomware message), but it can check that indices are well-formed, and file checksums match the uploaded contents. Obviously it should also be run on trusted machine.

Not sure what this whole "blockchain" comment was about.