Signal
About
Signal is end-to-end encrypted open-source messaging software available for Android, iOS, Linux, MacOS, and Windows. It is tied to (and identifies, when connected to other users) the phone number of each user; it's not clear why this is so.
Installation
Mobile: Android
Find "Signal" in the Google Play Store and install it. Allow it to access "contacts and media" and "make and manage phone calls" when it requests permission. It will ask for you phone number, but should be able to detect it automatically. It will then send you a verification code, which it may be able to detect automatically; after that you can set up a profile (i.e. enter a screen name for identifying yourself to other Signal users). This will default to your Google user screen name. You can also allow Signal to be your default SMS/MMS app; this is not required, and can always be enabled later.
Post-Install Setup
To be documented:
- device fingerprints and all that kind of stuff that I don't really understand.
- Question: how do you add someone who already has Signal installed? The only way I can find to add a new person is to "invite" them, which just sends them a text inviting them to install Signal.