The alternative is having the server know who is talking to whom. Further, phone numbers provide a valuable bootstrap to connect with people.
Other secure messengers have chosen a different design than Signal. This means you can choose the one you prefer.
It's clearly a lot higher data overhead, but that'd acheive phone numberless accounts without signal knowing 100% A is talking to B.... Only that 'A' might be talking to 'B'..Or C..or D.. Or sending decoy msgs intended for nobody.
Settling for phone numbers on a privacy based messenger because it's too hard to do an alternative implem is a cop out I feel. What do you think of the above proposal?
How are you going to do this without getting this person's public key? And how are you going to get their public key without asking signal?
So signal knows you requested all your contact pubkeys, that you sent a duplicate broadcast to all contacts, obscuring who it was intended for... that could be 0-n of m persons.
Regardless, I don't know why they are pushing in a somewhat unregulated, volatile cryptocurrency that will be used by extremists, terrorists and the like who in no doubt will not only use it to fund their activities and will be sitting in their group chats but now they can change their phone numbers to hide even further?
The road to hell is been paved with good intentions. Hasn't it? But at least Wire does not still require a phone number, nor does it have silly cryptocurrencies in their product for pump and dump purposes.