I'm currently working on this. So far, recognition of encrypted text and decryption works fine. However, it breaks Gmail if the text is part of an email there - only reloading get's it to work again.
The plugin I'm using was compiled on Ubuntu x64 and probably doesn't work anywhere else. It was written using firebreath, basically it's just a wrapper to gpg.
Since I have zero experience with JS, I'm thankful for any help. Code is on: https://github.com/Mononofu/CryptoChrome
The plugin I'm using was compiled on Ubuntu x64 and probably doesn't work anywhere else. It was written using firebreath, basically it's just a wrapper to gpg.