If they did, they would be the one holding the keys, not the user. The proposed solution also ignores the new-device case. If you install Twitter on your new phone, log in, and look at your DMs,you expect the whole history to be there. But if messages are encrypted for each device at time of transmission, then the new phone starts blank.
https://github.com/WhisperSystems/Signal-Desktop/issues/723
If they did, they would be the one holding the keys, not the user. The proposed solution also ignores the new-device case. If you install Twitter on your new phone, log in, and look at your DMs,you expect the whole history to be there. But if messages are encrypted for each device at time of transmission, then the new phone starts blank.