You can start communicating securely in just three steps:
1. Register with a unique username.
2. Agree upon a simple password with your friend which can be used to confirm each other's identity.
3. Finally, add a new user within the app by entering your friend's username along with the password from the previous step.
After your friend has confirmed the request and also entered the correct password, your two devices will automatically perform an authenticated key exchange (using the JPAKE protocol) which generates a shared encryption key to be used to encrypt/decrypt any of your transmitted messages.
The key exchange will only be successful if the provided passwords match each other, which means that you haven't to worry about people impersonating your contacts, or a man-in-the-middle attack taking place.
All message encryption is done on the end device (using 256-bit AES-GCM), meaning that your messages and encryption keys are not stored on a third-party server that is out of your control and vulnerable to attack.