this post was submitted on 16 Mar 2024
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It's actually fairly simple: if the server never has access to the keys or the plaintext of messages (or calendar events, etc.), then you need a client tool to handle decryption and encryption operations.
They use PGP, and they have implemented this feature in a way that it's completely transparent to the user to make it mainstream. So they chose building dedicated tools (bridge, web client), rather than letting users use their own tools, because the PGP tooling sucks hard and it's extremely inaccessible for the general population.
This means that you need a fat client, whatever you do, or otherwise the server will have access to the data and there is no e2ee. Instead of using enigmail or other PGP plugins/tools, they built the bridge.
Proton stores your keys, and you have the decryption password. How do you think they handle password-based logins? Only the user should ever generate and store the private key. All they need now is your decryption password & they can read your messages. This is reason #1 not to trust Proton.
It isn't transparent, because most users aren't running their own frontend locally and tracking all the source code changes. They've already violated the first rule of PGP privacy by having your private key. Now you're merely trusting them to not send you a custom JS payload to have your decryption password sent to the server. How many users are actually utilizing their hidden API to ensure that decryption/encryption is only done client-side? If they have your private key, how many users do you think are using long enough passwords to make cracking their password more challenging? This is reason #2 to not trust Proton.
This is just entirely inaccurate and you've failed to provide any "proof' for your generalizations here.
If you actually understood PGP you'd know you can generate and use local-only keys with IMAPS and have support to use any IMAP client. Furthermore, the other apps by Proton like Proton Pass, Calendar, etc... all use undocumented APIs that they have yet to implement in their bridge using standard protocols like CalDav/CardDav/JSON or whatever else in order to be able to integrate with local tools. There is no security benefit in their implementation other than to lock you into a walled garden and give you a false sense of security.
Proton stores an encrypted blob.
"All they need now is your private key". It's literally a secret, they use
bcryptand then encrypt it. Also, "they" are not generally in the threat model. "They" can serve you JS that simply exfiltrates your email, because the emails are displayed in their web-app, they have no need to steal your password to decrypt your key and read your email...Probably we misunderstand what "transparent" means in this context. What I mean is that the average user will not do any PGP operation, in general. Encryption happens transparently for them, which is the whole thing about Proton: make encryption easy and default.
Again, as I said before, they control the JS, they can get the decrypted data without getting the password...? You always trust your client tooling. There is always a point where I trust someone, be it the "enigmail" maintainers, Thunderbird maintainers (it has access to messages post-decryption!), the CLI tool of choice etc.
I mean, their clients are open-source and have also been audited?
I don't know. But here we are talking about a different risk: someone compromising Proton, getting your encrypted private key, and starting bruteforcing
bcrypt-hashed-and-salted passwords. I find that risk acceptable.See other post.
Care to share any practical example/link, and how exactly this means not having a fat client that does the encryption/decryption for you?
Right, because *DAV protocol are so secure. They all support e2ee, right...? There is a security benefit, and the benefit is trusting the client software more than a server, especially if shared. You can export data and migrate when you want easily, so it's really a matter of preference.
You are awesome!