Briar is a totally safe and secure private messaging app for communicating one-on-one with manually-added contacts. Conversations held on this app don't pass through a central server at any point. Instead, they're synced directly between the users involved.
To add a contact to Briar, you'll have to connect with them directly. You can't do it by text, photos, or anything else. Basically, they scan your QR code, and you scan theirs. Only after that can you start talking. This way, no one can impersonate anyone else, so you can rest assured that you're talking to the right person.
Briar is a powerful private messaging app especially well-suited to journalists, activists, and anyone else who needs a completely secure and reliable way to communicate.