BackBlazes stand on this, from the link:

Question:
I Don't Trust You, but I am Expecting an Honest Answer.
"If I opt to password-protect my private key, are BackBlaze servers still able to decrypt my data?
(For instance, by sending the password to the server where my private key is stored and decrypting the private key on the server)
Or is my data only able to be decrypted on the client?"

Answer:
ABSOLUTELY NOT. Once the password is set do not forget it, there is no way to recover it.
Once protected by a private encryption key Backblaze can only decrypt the backup files when the user
supplies the password. This is done during the restore process and the supplied password is never
saved on our systems, although never to disk, only to RAM.

What it Comes Down to is Trust, but, Unfortunately, I Just Can't Trust You.
"Having the private key outside my computer is unacceptable.
The unfortunate thing is that I can't trust you. I'm not allowed to trust you.
So, I guess my question is why do I have to? It makes most sense that I shouldn't -have- to trust you..."

I understand. What you are describing is conceptually perfect and provably more secure than what
Backblaze provides , unfortunately it is not easy to use.
Backblaze focuses on ease of use. It is backup for people who need backup and "pretty good security" and
who aren't computer professionals. It is not a perfect choice for all users on earth, you are unfortunately outside our scope.

Take our default security model -> it is about as secure as a Facebook account.
It uses a username and password. You can recover (reset) your password if you have access to your email.
That mode is good for many, many people on earth, people who have pictures of their children they don't
want to lose. Music they would rather not repurchase. And a few Quicken docs that they would not like a
malicious person to have, but they will not DIE if somebody reads them. And it's SUPER convenient to
recover their password. What a great system!

Our second level is really, really much more secure. You cannot recover the password
to access to your email account does not give you access to the backup, and even a malicious
hacker in our datacenter could not possibly compromise your data. Now while it is more secure,
it is also harder to use -> if you forget that password you have actually lost the backup, your
wedding photos are gone forever. That's very secure, but it's not as secure as what you describe.

We stand by our reputation as trustworthy, careful programmers who have worked
in the security field for over a decade.
You can check us out on LinkedIn, through colleagues that have worked with us, through the
publicly traded companies that have acquired our companies in the past.
Here is our team page: https://www.backblaze.com/team.html We live and work in Silicon Valley,
we've been here for 20 years, and we plan to keep doing this for a long, long time, and therefore we
have LOTS of interest in keeping our reputations rock solid and utterly clean.
Previously we fought phishing fraud, fought email viruses, and fought spam at a company called MailFrontier.
We are totally customer focused and all around good people, ask ANYBODY.
If you come here to our offices, I'll buy you a cup of coffee.