If you’re going to use BackBlaze’s software, which has access to all your files, you have to trust Backblaze as a company. If you don’t trust them, don’t use their service. Simple. There is no circumstance under which you can both distrust them and run their software. (Try tarsnap instead.)
So now the question becomes: what threats are you protecting yourself against?
For me, it’s:
- malicious employees accessing my data
- a security breach giving outside actors access to my data.
Encrypting the backups and encrypting the private key protects me against these threats.
My “restores” aren’t protected against these threats, because they’re not encrypted (as of 2019 when this FAQ was written), so that’s a gap. It’s one I’m willing to put up with because I can mitigate the risk by not leaving restores hanging around.