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Time to get serious with E2E encrypted messaging
(techcrunch.com)
This is a most excellent place for technology news and articles.
I used to do something like this before Signal became a thing. We used to use OTR via the Pidgin OTR plugin to send encrypted messages over Google Hangouts. Funnily enough, I'm pretty sure Pidgin supports Discord, so you could use the exact same setup to achieve what you described.
It was pretty funny to check the official Hangouts web client and see nonsensical text being sent.