I am looking for a way to backup my private key for the Signal messenger application. Nothing has worked so far, and I am curious whether anyone can confirm or deny that Titanium backup will save and restore the private key of a Signal install.

  • I don't know about the Signal app and the private key you speak of but maybe that is stored in hardware. If your device supports that. – miva2 Nov 21 '16 at 15:19
  • @miva2: Unlikely, since otherwise I would probably not have lost the private key twice after a reinstall. Secondly, I'd consider this a very insecure method of storing the private key, I don't think Signal would do that. – Jesko Hüttenhain Nov 21 '16 at 18:29

Signal 4.17.0 introduced encrypted backups. This is the preferred migration path. Also the Titanium Backup route does not work in current releases.

Previous Post

I just tried this and it worked flawlessly.

After restoring Signal on your new Phone you should re-activated your connection by unregistering and re-registering to the Signal servers. As of now you can do this in the Signal Settings > Advanced tab by toggleing Signal messages to de-activate then re-activate [1]. In this Process you will have to re-verify your phone number and you'll have to reconnect your Signal-Desktop clients afterwards.

You won't loose your Private key or your Signal-Desktop messages though.

[1] https://support.whispersystems.org/hc/en-us/articles/213190487-Why-is-there-a-delay-in-receiving-messages-

  • Just tried this, with Signal 3.30.4 and upgrading my phone from Android 5.0 to 7.1 - still works perfectly. I initially didn't un-register/re-register - but push notifications weren't working properly, so then I did. As @m-schulz-narres says I needed to re-connect the Signal Desktop clients I had but they did not lose their previous messages. One thing to note is that group messages may get messed up by re-registering - you'll need a friend in the group to first accept your new safety number (you can directly message them), and then update the group (i.e. change the name or picture). – seanlano Mar 7 '17 at 8:40
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    Even though I do trust the author of this answer without reservation, I can now confirm as well that this works indeed. Upgraded from Lollipop to Nougat, installed Signal and restored the data backup, and everything works. – Jesko Hüttenhain Aug 8 '17 at 16:40

Titanium Backup does backup the key, but there's something internal to Signal that realises that it's installed on a new phone and refuses to use the old key.

Set recurring backups inside Signal instead.

Be aware that when restoring:

Place the .backup file in the sdcard root directory. Putting it under sdcard/Signal/backups will have the file NOT be read, but no error message given, either.

The backup is only read correctly if the metadata is displayed in a confirmation step. This took me hours to work out. >:|

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