> It could also pass back Bob's answers, and so Alice could have what appears to be a normal conversation - except that Alice only sees single ticks, instead of double blue ticks.
No, it can't do this, because Bob's answers contain the "delivery receipt".
Hence, the attack doesn't work on conversations.
EDIT to reply: messages are sequential and "delivery receipts" are messages, so it would be visible if the attacker dropped some but not all messages. AFAICT.
So, given that, it would seem that a compromised server could pull a whole conversation (if people overlook the single tick mark), as claimed in the article?
Ah. If that is so (and it's not obvious - clearly you can get delivery or even read receipts without Bob sending an answer), then it would seem that a bad server could only intercept a long monologue, indeed, but not a conversation.
No, it can't do this, because Bob's answers contain the "delivery receipt".
Hence, the attack doesn't work on conversations.
EDIT to reply: messages are sequential and "delivery receipts" are messages, so it would be visible if the attacker dropped some but not all messages. AFAICT.