[ikawe]

https://signal.org/blog/sealed-sender/

The short version is: Traditionally, Bob needed to “log in” to be able to send a message to Alice’s inbox.

With Sealed Sender, Alice gives Bob a credential that allows him to message her from now on without logging in.

Only Alice can tell that the message she received is from Bob.

There’s some subtlety around bootstrapping these credentials and preventing abuse which means that not every message can be sent as Sealed Sender, but the vast majority are. Read the blog post for the authoritative explanation.

There’s an option in the app settings to make visible which of your messages were sent without identifying your client to the server if you’re curious.

[rendaw]

Ah thanks, okay, I'm not sure I'm missing anything in that case.

But if so, doesn't signal still know that alice and bob are communicating because it's transferring messages between them? Even if Bob doesn't log in IP B is still sending payloads that eventually get delivered to IP A, and if law enforcement later asks signal for logs they could be correlated.

[happymellon]

Indeed, at some point in time a byte has to move from point A to point B, and unless you random VPN to a different location the source and destination IPs can be identified.

Even if they can't read it, a hostile government won't care.

There is only so much you can do against a really determined adversary thats well funded. I just want a Signal that doesn't tie everything back to a phone number.

[EGreg]

What messages can’t be sent as sealed sender?

I arrange to tell Alice in an encrypted chat that I will be doing a drop on X url after Y time and to watch it.

Alice comes picks up the drop. Done.

PS: This is another great use for cryptocurrency. When you don’t want to use account-based charging, then you allow anyone to prepay for the resources with crypto.

[ikawe]

For example, before you have Alice’s sealed sender authorization credential, you cannot send Alice Sealed Sender.

This happens upon initial contact and after Alice revokes her credential (which can happens if she blocks someone).