Because we only know what the client does, and have no clue on the server side of things, allowing Proton to do any manipulations with the data. Not ideal when you consider it for password storage.
Because non-obvious backdoors can be added to the client that break or circumvent encryption (looking at you, xz), stealing all of your passwords, and no one will be able to raise the alarm just by looking at the server code.
Open-source backend allows to generally avoid this situation, while also potentially rendering you able to self-host if you’re paranoid.
This was a real concern with MEGA back in the day (after Kim said you should no longer trust them) and a big reason why I prefer to use standalone client apps that I can control the source of.
Avoid why?
Because we only know what the client does, and have no clue on the server side of things, allowing Proton to do any manipulations with the data. Not ideal when you consider it for password storage.
if the client is e2ee and you can control that, then why is the server relevant?
Because non-obvious backdoors can be added to the client that break or circumvent encryption (looking at you, xz), stealing all of your passwords, and no one will be able to raise the alarm just by looking at the server code.
Open-source backend allows to generally avoid this situation, while also potentially rendering you able to self-host if you’re paranoid.
Sorry, I meant “assuming one has complete control over the client source” where the remote cannot just change it on you.
I mean they can make a sneaky update to the client that introduces such changes.
Sure, if you won’t update your client, this won’t affect you, but would potentially open you up to other security vulnerabilities.
This was a real concern with MEGA back in the day (after Kim said you should no longer trust them) and a big reason why I prefer to use standalone client apps that I can control the source of.
What should I use then?
Something like Vaultwarden if you care about cloud sync, or KeePassXC if that’s not on your priority list.