There is a Chrome extension that does something like that: https://github.com/google/end-to-end
Obligatory warning: it's in an alpha state according to the readme, so you shouldn't use it yet for real.
Obligatory warning: it's in an alpha state according to the readme, so you shouldn't use it yet for real.
load scripts, css, images. show native window (clearly different than anything js can do) with that rich text editor inside. user types message in, system encrypts (and/or signs) the message. regular html page sees the result.