E2EE Design Plan

When a user reports a message, the client has to send the message it has decrypted to the instance admins. The problem with this is that it opens the door for a malicious client or user to report fake messages to the instance admin. To prevent that, we can enforce that the official client needs to cryptographically sign every message they send before encrypting it

That sounds quite complicated, and also likely vulnerable to context switching attacks (for example moving "so beautiful " from a convo about new years fireworks to a convo about 9/11). (Such attacks can be prevented, but only by adding even more complexity.) Instead, I propose a slightly different solution: When a user reports a message, the client sends the message key to the instance admin. (But I do agree with client signing the ciphertext, and server verifying that signature.)