Well, matrix can to multi-device usage great and has E2E, so I don't see why that would be a hard requirement or even any kind of requirement.

Because at least according to the Threema devs, doing e2e multi device in a secure and anonymous way is not trivial.[1] Maybe matrix solved that problem, maybe they don't care...

[1] https://threema.ch/en/blog/posts/md-architectural-overview-i...

I guess it depends what you need and what is "secure and anonymous". Matrix probably leaks a ton of metadata.

In practice it works by each device having their own encryption key and then those devices are bound together with a cross signing key, so your peer can robustly identify all your devices at once (and the list of devices can change as long as they are bound by the cross signing key). Certainly the server is able to correlate device ids (and thus keys) and IPs.

The way threema does it sounds a bit how room encryption works in Matrix amond multiple clients.

What kind of multi-device issues do Signal and WhatsApp have exactly?

Granted I've never used WhatsApp, but I've been using Signal for like 5 years now on my phone and on my laptop with absolutely no issues.

Seriously? Both only have crappy web apps that you basically tunnel messages through your phone (at least that's what I remember) and are tied to a specific mobile device with entire companies being built around the apparently extremely complicated task of moving WhatsApp messages around.

Meanwhile, the Telegram desktop client is at feature-parity with the phone app with both running entirely independently on as many devices as you want.

Signal messages are not routed through your phone. Reach has it's own independent queue and the phone can be off and you'll still receive messages on the desktop client.

I would also state that it is unfair to compare an app that doesn't have to worry about your privacy and solving real engineering problems vs basically making a web app that can easily sync your data because it's all stored on someone else's computer.

If that's the level of privacy you're setting you may as well use email for communicating. It's federated, it's easy to use, and everybody has one.

All that said, I do agree the Signal desktop app needs some work, but they'll get there eventually, and in the meantime I don't have to wonder if any of my data will be leaked to anyone outside of my intended recipient.

> basically making a web app

Funny you say that because Signal is the one with a crappy Electron app which is definitely a deal breaker for me. I mean I lose E2E with Telegram but gain really well designed and featureful platform apps that are native and non-gimped desktop apps (and a functional linux client. Signal's Ubuntu client just crashed for me).

Signal none, WhatsApp still cannot be used without being activated on a smartphone/tablet, and cannot be activated on more than one mobile device.

I don't think you can even use the same Signal account on two different iOS devices, much less desktop. Their desktop apps just link to the phone's app.

WhatsApp is a total joke, it loses media (IIRC this includes audio messages as well) people send you after a very short time even when you use it on a single device, so talking about multi-device usage is completely out of the overton window.

WhatsApp does not have multi-device, so technically it has no issues with it.

(for any sensible definition of multi-device)

Good point. I use irc more than any other IM and nobody ever complained about lack of e2e there. When the usecase is more about meeting new people it doesn't apply as much.