1y ago

Why Not Store Encrypted Emails in Plaintext Locally?

Clients like Thunderbird are great because you have everything stored locally so you can easily search offline. They also support encrypting and decrypting emails in PGP. However, they seem to have the same limitation as protonmail where you can't search through encrypted emails.

I know that protonmail can't just store your key at their server since that would defeat the purpose, so the emails are all ciphertext to them right? But in Thunderbird, you already have the key and decrypt everything all the time. So why can't you skip the middleman in your local machine and store everything locally in plaintext? It's not less secure since if your local machine is compromised, your private key is also compromised.

Or at the very least give us the option and have a slightly less secure but much more convenient option.

19 comments

I've been trying to move away from email as a document server.
Anything that's important / I might want to reference later gets exported to a secure paperless-ngx instance where it's neatly categorized and easily searched. I then delete it from my inbox.
- Came here to ask about paperless and the myriad of versions, even though it's off topic.
  
  Paperless-ngx installed via docker-compose is super easy. I have it on a luks-encrypted vm only accessible via tailscale.

If you're in Linux, you can use eCryptfs to setup a private encrypted directory, move the ~/.thunderbird directory into it and just leave a symlink to it in your unencrypted home directory. Then you can store your emails in plain text in the encrypted private directory.
It's not even complicated to set up: most Linux distributions are setup so that the private directory is automounted upon login: when you're not logged in, your data at rest is encrypted. It only becomes readable when you're logged in.
Both my Thunderbird and Firefox directories are stored in my private directory.
- This does not answer the question. OP wants to Thunderbird to decrypt PGP mails. Yes, it makes sense to use an encrypting fs, but we are still missing this thunderbird feature.

Just as it inconveniences you to have to decrypt to search, it would similarly slow down anyone malicious who gains access to your machine.
Am in favour of allowing users to decide which features are best for their needs, but this seems like it would be easy to forget to reinstitute local encryption after a search, so can also understand why developers prevent storing in plaintext.
- You can't search encrypted emails, period. The way I see the benefit of encrypting emails is to not have them compromised in the cloud servers. But on my own machine, if someone gains access to the files, then it's all ogre. Maybe that's just me IDK.
  
  Point is, one can decrypt each email individually. That slows an malicious attacker rummaging in your device from finding what they are after as much as it does you.
  You wouldn't be alone in wanting this feature, but for those who need rather than prefer to encrypt, the option to store locally in plaintext is a major risk. On balance it seems better for developers to pay heed to that than to our preferences.
  For the rest of us, we can download the emails we wish to refer to with ease, or we can create aides memoire to make it easy to locate specific emails later.

Locally, an attacker still needs to know your password. A strong password can make it too expensive or impractical to brute force.
- Do you have to put in your password on every session in protonmail? If not, then that means that either the key is unencrypted and is stored somewhere else as plaintext or the password is stored somewhere also as plaintext, which would defeat the purpose.

Honestly, I can't think of a good reason. This is just how email has always worked. What Thunderbird stores locally is identical to message on the server. It's not decrypted because no conversion happens when syncing mail.
I agree, it would make sense to keep plaintext emails locally or on a trusted server for practical reasons.

Protonmail now supports searching in the content of all your mail, though.
Or at least the web client. It will ask you to download all your mail, and it will make an encrypted search index on your computer.
- That's cool but I like to have a central client for all my email providers. I've decided to go to fastmail which is good enough for my threat model. The thing that really convinced me is their blog post.
  The main thing I care about is the security of the text in transit, and the philosophy of the service I'm using. All respectable mail providers use TLS (even gmail and outlook) but I don't like their advertiser dependent business model. Proton, tutanota, and I think startmail do respect privacy, but I believe it's dumb to depend on an external server if you're that paranoid about your communications that you need to have your email using PGP. Just encrypt your own stuff and tell the other party to do the same. Or self host everything.
  
  fastmail
  That's a paid service, right? I don't know much about them, they may have other pros too, but proton also allows you to use your own email client if you're in a plan.

I think Tutanota (or just Tuta now?) does this, since search works correctly.
I think not using PGP helps Tuta a lot with this, since PGP is really outdated and does not play well with modern features.

I am annoyed by this too. The big limitation would have had you could not use IMAP as that is remote.
The other issue is implementation. It would be easy to forward or attach or just store unencrypted in an insecure way which may not be desirable. Frankly for what I do I would prefer Thunderbird decrypt on receipt but place all content in a vault. If one wanted to add some more restrictions one could make it hard to forward by accident mail that was originally encrypted.
The big issue with PGP has always been a combination of bad implementations and key distribution.

This may be a long shot, but it's what I do, so it might be an option: Set up a crypto gateway like CipherMail which will automatically decrypt inbound email and sign/encrypt outbound. The result is that your Thunderbird will never get to see an encrypted email, decryption is handled transparently before it hit's your inbox. Obviously, if you don't trust your email provider, this is not an option.
This isn't simple and hence not for everyone, also comes with dependencies on your email provider, but it works flawless for me ever since I set it up. I run my own email server, hence adding in CipherMail wasn't a big deal.

I feel like you'd get this with the Protonmail Bridge. It acts as it a email provider on your local network, and handles the encryption stuff itself. I believe Thunderbird sees and stores the email it sees through that as plan text.
https://proton.me/mail/bridge

19 comments