So I've had this idea on my radar for a while, but here was my angle:
What if you made this a web extension, and took control of textareas everywhere on the web?
Why not be able to turn any message delivery (ex. facebook messenger) into a delivery for private messaging. What keybase used to be (a repository for peoples' public keys) would be a great integration point -- if the person has a public key listed (maybe in a twitter bio, etc), you can send them messages that are encrypted with a generated symmetric key + nonce (the usual safe enveloping rigor you need) -- and every message you send them might start with the URL or the actual encrypted message itself (and it would be up to them to use the extension to decode it).
It would be easy to get this working with a browser (a sufficiently powered web extension would do), but a bit harder to get it working on phones since the APIs aren't QUITE there, but IIRC there are some screen scraping APIs that could actually work (as long as your read the screen text, convert that to a message, then decode etc).
My friend and I implemented this a couple of years ago. It is no longer maintained but the general ideas still apply. Very few social media sites use standard text areas which makes maintaining compatibility a total PITA.
What if you made this a web extension, and took control of textareas everywhere on the web?
Why not be able to turn any message delivery (ex. facebook messenger) into a delivery for private messaging. What keybase used to be (a repository for peoples' public keys) would be a great integration point -- if the person has a public key listed (maybe in a twitter bio, etc), you can send them messages that are encrypted with a generated symmetric key + nonce (the usual safe enveloping rigor you need) -- and every message you send them might start with the URL or the actual encrypted message itself (and it would be up to them to use the extension to decode it).
It would be easy to get this working with a browser (a sufficiently powered web extension would do), but a bit harder to get it working on phones since the APIs aren't QUITE there, but IIRC there are some screen scraping APIs that could actually work (as long as your read the screen text, convert that to a message, then decode etc).