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The way Wire does this, if I recall correctly, is that logging into your account (proving to the server you can authenticate) allows you to push up a new device

The way Wire does this, if I recall correctly, is that logging into your account (proving to the server you can authenticate) allows you to push up a new device public key, which you can see as your device fingerprint in the UI. A conversation between two users with multiple devices is really a group chat, with pairwise ("client fan out") double ratchet sessions going on. When you do this, your other devices are informed of the account change by the server, as are people you communicate with (if they've previously marked your account as trusted, changing any devices on your account changes that). This isn't much different to Signal: ultimately the server acts as a key directory in both cases. The problem with this approach is that it doesn't scale well at all. This is why Facebook, Wire etc are working on MLS (Messaging Layer Security) which is basically "add trees" so group chat scales better.

Reelin 7y ago
Thanks for explaining, that makes much more sense. It seems to me that double ratchet is really to blame here. Without it, you could simply share a single key across all devices. With it, your choice is to either deal with this sort of complexity or to set up a trusted proxy in the middle. It's a bit strange actually. There's this constant mantra of having to pick either security or usability. We now have readily available means for usable _and_ reasonably secure E2E, but the crypto nuts go and add additional "must haves" that once again make it difficult for the average person to use. An aside: Instead of authenticating with a central server to add a key (as you've described Wire doing), why not handle this client side via X.509 certificate chains? This is very mature crypto and seems far more flexible. It would enable use of standard PKI token hardware for managing your root identity, allow fully offline enrollment of new devices, and provide cross signing for various purposes (changing your root identity, setting up a web of trust with a group, integrating with a corporate environment, etc).
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Reelin 7y ago

Thanks for explaining, that makes much more sense. It seems to me that double ratchet is really to blame here. Without it, you could simply share a single key across all devices. With it, your choice is to either deal with this sort of complexity or to set up a trusted proxy in the middle. It's a bit strange actually. There's this constant mantra of having to pick either security or usability. We now have readily available means for usable _and_ reasonably secure E2E, but the crypto nuts go and add additional "must haves" that once again make it difficult for the average person to use. An aside: Instead of authenticating with a central server to add a key (as you've described Wire doing), why not handle this client side via X.509 certificate chains? This is very mature crypto and seems far more flexible. It would enable use of standard PKI token hardware for managing your root identity, allow fully offline enrollment of new devices, and provide cross signing for various purposes (changing your root identity, setting up a web of trust with a group, integrating with a corporate environment, etc).

telegrammember 7y ago
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