Signal-desktop: [Feature request] Synchronise all messages from mobile app during desktop app installation

[fsoullier]

Bug description

When installing the Signal Desktop app messages previously exchanged on the mobile app are not synchronised.

Steps to reproduce

Install Signal Desktop app.

Feature request

Synchronise Desktop app messages with current mobile app messages enabling a true seamless experience between mobile and desktop. I read somewhere that not synchronising both apps was a feature. Why would anyone want that? The Desktop version advertises "Seamlessly move your private messaging experience from your mobile phone to your desktop computer and back." but upon installation no messages are available.
Should there be uses cases when one users would not like his/her messages being imported in the desktop app, an option should be given not to import during installation.

[NinebitX]

Is this a dupe of https://github.com/WhisperSystems/Signal-Desktop/issues/444?

[fsoullier]

Yes, it is a dupe of #444. I find however the title of #444 misleading as you can understand that import/export is requested whereas the comments mention that messages are not synchronised between app and desktop version. I would suggest using the word synchronisation (which is was also missing from my feature request) to be more precise.

[peacememories]

I think this would be a potential security concern. As I understand it the reason you do not get your old messages when you add a new client is the forward secrecy inherent to the Signal protocol (getting access to the keys of a client does not grant you access to any messages sent so far).
Of course one could prompt the mobile application to sync over the messages via another channel, but this should also be discussed as an attack vector in my opinion.

[fsoullier]

I did not know about forward secrecy, now that I do I understand the limitations it makes sense. However, it does negatively impact user experience when setting up a new device. Any workaround would be highly desirable.

As you mention, a prompt could let the user decide, maybe a confirmation message sent to the first installed app could further strengthen security? I'll let the experts devise the best way to deal with this and ponder the risks of attack but the feature is definitely wanted.

[dhbuckley]

Non techie user opines: Sync s/b an option. Totally get not to mandate it as default but believe one should be able to choose at desktop install and subsequently. What is current behavior across multiple desktop installs, btw?

Mostly, thanks for what you do.

[stheid]

Forward secrecy only demands to:

• [technically] re-encrypt the messages
• [permission] allow on the mobile app to resend old msg to the desktop
• [wifi] to prevent high traffic on the server one could allow sync only via wifi

There is no unsolvable security related reason not to sync.

[magynhard]

I still find it hard to believe that this feature hasn't been addressed yet. It keeps bugging me.

[bckspc]

Non techie user opines: Sync s/b an option. Totally get not to mandate it as default but believe one should be able to choose at desktop install and subsequently. What is current behavior across multiple desktop installs, btw?

Mostly, thanks for what you do.

Yes. I would even add that this could be set as a user profile setting disabling loading of old messages all together but allow you to enabled it and then do it per client install. Maybe at work I only want my recent messages but at home I want the full sync.

[Scindix]

If security is the issue would it at least be possible to synchronize the messages via ADB/USB?