When you opened discord you will get a window to create your database (stored locally), once it's done & ready, you can simply enable the encryption by toggling the lock icon visible to the channel's top and you can chose the key used besides that. You can go in the menu by right clicking the lock icon. DM channels have other options than group channels for global encrypted communication.
It is totally open-source!
More information on: https://github.com/HyCore/ShulkerRoadCrypt/
Extore is a team of professionals who are passionate about creating extensions for web browsers. This devotion also gives us opportunity to appreciate work of other people. We get inspired by useful, open source extensions made by developers all over the world. Our strong belief is that one should share helpful add-ons with others. That’s why we’d like to present you our ever-growing list of favourite extensions that have inspired us. Moreover, as you probably have already learned, sometimes struggling for the best brings an end to the good. Talking about add-ons it often turns out that an upgrade is worse then previous version. Also it can become really tricky to get back to the beloved version of your favourite extension. That’s why we’re going to make not only the latest, but all versions of our favourite (and we hope yours too) add-ons available for download. No more compromises, just stick to the version you really like!