12.06.2019 by Lyudmila Vaseva and nico

How to install and use Signal messenger without a smartphone

A step-by-step manual

Signal is an encrypted end-to-end messenger for Android, iOS and Desktop OS (Windows, MacOS and Debian). In this tutorial we discuss how to install and use it without a smartphone.

Signal-cli + Signal-Desktop

Signal-cli is a command line interface for Signal. It’s used to register a new signal account and then link a Signal-Desktop app to this account. If you really use Signal without a smartphone, signal-cli functions as the single-point-of-truth.

Go to the following link and download the latest signal-cli release: https://github.com/AsamK/signal-cli/releases/latest

In our case this is v0.6.2

  $ wget https://github.com/AsamK/signal-cli/releases/download/v0.6.2/signal-cli-0.6.2.tar.gz
  $ tar xfv signal-cli-0.6.2.tar.gz
  $ cd signal-cli-0.6.2

To be able to use Signal you have to register yourself with a phone number (doesn’t has to be a mobile number).

  $ bin/signal-cli -u YOUR_NUMBER register

You will then get a SMS with a verfication number if it’s a mobile number or else a call. You use this number then to verify your account:

  $ bin/signal-cli -u YOUR_NUMBER verify VERIFICATIONCODE

Install the latest version of Signal-Desktop from here: https://signal.org/download/

Now you have to start Signal-Desktop and extract the actual QR-Code. For this, start Signal-Desktop. It should display a barcode to link your Signal-Desktop app to a Signal device. You can either decode the barcode on your local machine or use a smartphone to scan the barcode.

Android:

  1. Install Barcode Scanner on your device
  2. Scan barcode and tsdevice-Link should appear

Linux:

  1. Toggle Developer Tools, go to Network Tab
  2. search for data:image/png entry, click on it and the actual barcode should be displayed
  3. Right click on the bar code to save it for instance as /tmp/qr.png
  4. use zbarimg (zbar-tools) to decode it: $ zbarimg /tmp/qr.png QR-Code:tsdevice:/?uuid...
  5. Copy tsdevice-Link

Now you can link your Signal-Desktop to your Signal account through signal-cli:

  $ bin/signal-cli addDevice -u YOUR_NUMBER --uri "tsdevice:/?uuid..."

Add contacts

We use signal-cli daemon to synchronise contacts (with names^^) with our Signal-Desktop instance.

On Ubuntu, you have to install libunixsocket-java package (otherwise the signal-cli daemon can’t start)

Fill in contacts in the signal-cli config: .local/share/signal-cli/data/YOUR_NUMBER in the dict

   "contactStore" : {
     "contacts" : [ {
       "name" : "name",
       "number" : "+49xxxx"
     }, {
       "name" : "name2",
       "number" : "+49yyyyy",
     }]}

Start signal-cli daemon:

  $ bin/signal-cli -u YOUR_NUMBER daemon

And then synchronise contacts in the Signal Desktop App (File->Preferences->Contacts->Import Now)

Troubleshooting if signal-cli daemon reports following error

Envelope from: <yournumer> (device: 2)
Timestamp: xxxxx
Exception: org.whispersystems.libsignal.InvalidMessageException: No valid sessions. (ProtocolInvalidMessageException)
Failed to decrypt message.

then:

  $ bin/signal-cli -u YOUR_NUMBER send -e -m "foo" YOUR_NUMBER

In the same config, set the Active parameter for all groups to true, in order to be able to send messages in groups.