Crypto Messenger is end-to-end encrypted messaging application. It's a part of my Cryptography application and all it's workings are describe at my website. It's not intended to replace any bigger messaging applications. You can find link to documentation at app's about dialog. New version notes.
Download the installation package of Crypto Messenger 1.2.7 for free and take a look at users' reviews on Droid Informer. The app works flawlessly on Android 5.1 and higher. The download of this application doesn't contain viruses or any kind of malware. Nitramite is the developer of Crypto Messenger that can be found in the Communication category.