[tptacek]

The paper goes into detail on the errors and how they compare to the normal experience of using Element, but I think that discussion kind of dignifies the situation, doesn't it? We're talking about a warning that essentially says "an unauthorized person is now decrypting your messages". This isn't a reasonable thing to "warn" people about it; in a secure messenger, your job is to prevent it from happening at all.

It's weird that we're even discussing this. In Matrix, group membership is key distribution, and it's controlled by the server! That's not OK!