[shriphani]

sender specifies recipient but the signal server cannot tell a group-chat message from a non-group chat message.

[rtpg]

so in this world signal still knows I'm sending to N recipients? Or is the fanout happening in a different way?

I guess I'm wondering if Signal still basically has enough info to make good guesses at group existence.

[shriphani]

Yeah I think you are correct that the protocol isn't safe from traffic analysis.