Hm, this makes me wonder, are there any hand-assembled TTL computers that can send UDP packets on the internet? ChaCha20 is easy enough to implement and simple enough that you could probably do encrypted chat between two almost-definitely-not-backdoored computers if so.

EDIT: though, I supposed you don't need your NIC to be trusted any more than your ISP's router, so an esp8266 might be sufficient.