2020-08-09 GPG and ProtonMail

I recently sent an email to somebody and got back an encrypted reply. That’s amazing! This is great! 😍

But wait a minute… How do I write them back? Like many people (like me!) they didn’t include their public key in their reply. Evolution told me that the mail was signed and encrypted, so I wondered. How was Evolution able to verify the signature without having their public key? But then I spotted that little help text: “This message is signed, but the public key is not in your keyring.” (I am using a dark theme and that particular help text uses black on nearly black…)

OK. I saved the email in mbox format and opened it in my favourite text editor. And there, on line 16:

Received: from mail-40131.protonmail.ch …

Right, so they have a ProtonMail account. But surely ProtonMail makes the public keys of their users … public? I found an answer on Reddit: use hkps:api.protonmail.ch.

How does that work?

gpg --keyserver hkps://api.protonmail.ch --search-key foo@bar

Remember that the reply I had received didn’t use the protonmail.ch domain for their email address. This is therefore still an absolute usability nightmare. But at least now I know. 😁


Nice! Do you use proton mail yourself?

Josh Rollins 2020-08-09 19:41 UTC

I switched my mail to Migadu because I wanted to use regular email clients.

– Alex Schroeder 2020-08-10 04:26 UTC

@sheogorath said that WKD should take care of key discovery:

gpg --locate-keys foo@bar

I’ll have to try it. If it works I’ll hate the fact that there are now two commands: search keys, which I have used for years, and locate keys.

– Alex Schroeder 2020-08-10 04:28 UTC

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