I've been waiting for Joplin Cloud to share notes with E2EE. And it now looks to me like E2EE is now possible for shared notes on Cloud.
Firstly, prerequisites. Note sharing needs a Pro Plan at minimum to share. Then, to collaborate on a shared notebook, you'll need a Pro Plan. So, a Pro Plan needs to be had by all parties to be involved in a shared notebook.
Now, on to encryption. At first, shared notes didn't have E2EE. I've sorted my findings by timeline, assuming that newer information likely supersedes old information.
2021.07.27: "If you share the note, E2EE no longer applies to that note."
- "I'm planning to add support for E2EE for shared notes and notebooks, but first I need to improve how E2EE works (started here)"
2021.08.09: "any shared notebook or note will not be encrypted"
2021.08.12: possible dependency for enabling E2EE on shared notes is merged.
2021.01.01: found that translation file for JP has a string that suggests E2EE is enabled for shared notebooks.
2022.01.01: E2EE specification mentions Public-private key pairs, which reads like they enable E2EE on shared notes.
- "At this point, both users have a copy of the key and can share notes over E2EE."
I hope this now means that even shared notes on Joplin now benefit from E2EE