Signal is operated by a nonprofit foundation which distributes a free phone-based encrypted communication app and prides itself on collecting as little data as possible. For that reason, it’s popular with people who care about their privacy. (Disclosure: I use this app as my default SMS app for texting as well as for foreign telephone calls).
But messaging apps — especially encrypted messaging apps — are a complicated business. Governments around the world really dislike encrypted messaging and often push companies to put in backdoors for surveillance and law enforcement because, yeah, criminals use encrypted messaging for all sorts of deeply evil things. But there’s no half step to breaking encryption, so companies like Signal often find themselves in the difficult position of refusing to help governments.
WhatsApp uses the Signal encryption protocol to provide encryption for its messages. But you can’t just look at that and then stop at message protection. WhatsApp does not protect metadata the way that Signal does. Signal knows nothing about who you are. It doesn’t have your profile information and it has introduced group encryption protections. We don’t know who you are talking to or who is in the membership of a group. It has gone above and beyond to minimize the collection of metadata.
WhatsApp, on the other hand, collects the information about your profile, your profile photo, who is talking to whom, who is a group member. That is powerful metadata. It is particularly powerful — and this is where we have to back out into a structural argument — for a company to collect the data that is also owned by Meta/Facebook. Facebook has a huge amount, just unspeakable volumes, of intimate information about billions of people across the globe.
It is not trivial to point out that WhatsApp metadata could easily be joined with Facebook data, and that it could easily reveal extremely intimate information about people. The choice to remove or enhance the encryption protocols is still in the hands of Facebook.
From a functional standpoint, both apps let you not only text, but make phone and video calls as well. To me, with very few exceptions, it is clear that Signal is the way to go - but can’t export a chat to a text file the way WhatsApp can).
Jeff