It gets more interesting when you think about the impact on groups. Sending an image to a group is enough for all devices associated with that group to be identifiable from CloudFlare's side, who additionally see a giant chunk of unencrypted traffic from the same client addresses going to other web sites. Given Cloudflare's less-than-straight approach to sales, it is astonishing the words "secure" and "Signal" ever appear in the same sentence.
CloudFlare get to see a fuckton of metadata from private and group chats, enough to trace who originally sends a piece of media (identifiable from its file size), who reads it, when it is is read, who forwards it and to whom. It really doesn't matter that they can't see an image or video, knowing its size upfront or later (for example in response to a law enforcement request) is enough
CloudFlare get to see a fuckton of metadata from private and group chats, enough to trace who originally sends a piece of media (identifiable from its file size), who reads it, when it is is read, who forwards it and to whom. It really doesn't matter that they can't see an image or video, knowing its size upfront or later (for example in response to a law enforcement request) is enough