To add someone to a Signal chat, you just need to open the chat's information page, where all the members are listed.

You can't change your phone number in the Signal app directly, but you can deregister your old number and then update the app as if it were new.

If you hadn’t heard of Signal before Monday, chances are you have now. The secure messaging app, available for iPhones and Android devices, has long been popular with journalists because of its robust ...