When you open the app, it automatically generates a random 2048 private-public key pair.
This key pair will be deleted every time the app is force closed. This means that all messages that were encrypted will no longer be decrypted - safe.
By default, without checking any of the checkboxes, the encryption is symmetrical where a cipher is used with a static key to encrypt and decrypt your message. The downside is that everyone with this app can decrypt your message. So it is better to use "Enable Keys".
Checkboxes:
Enable Keys - when checked, this enables encryption of your message using your recipients public key. Only your recipient will be able to decrypt your message using his/her private key (one to one communication)
Use private key for encryption - when checked, this enables encryption of your message using your private key. Everyone who has your public key will be able to decrypt your message (one to many or broadcast communication)
Credits:
<div>Icons made by <a href="https://www.freepik.com" title="Freepik">Freepik</a> from <a href="https://www.flaticon.com/" title="Flaticon">www.flaticon.com</a></div>