I've built a similar piece of javascript crypto: PasswordProtectMyFile.com. It's a single HTML page that can work with internet turned off. The ciphertext is another HTML page with all the javascript needed to decrypt itself.

It's open source: https://github.com/louissobel/ppmf

It's all in one html file, so it will work disconnected from the internet. Download or save the page, turn off your internet, open it in a browser, and encrypt with peace of mind (although the javascript could still use off-line storage and then next time you're online on the page access it, I guess).

It's a little clunky, but I do have a process in place for checking that the website matches the code: https://github.com/louissobel/ppmf/blob/master/bin/check_pro...

If you have to run a local program to verify the code on your web page, why don't you just put the code you are verifying in the local program?

The encrypted result of this tool contains all the code necessary to decrypt itself (in a web browser).

I'm not too familiar with GnuPG, so I don't know if that's different.

I'm reminded of those self-decrypting .exe archives that WinZip used to produce back in the day...

Any browser?

Tested and working with recent Chrome, Firefox, Opera, Safari 6.1+, IE 10+. https://www.passwordprotectmyfile.com/faq.

It uses, among others, the Blob API so will not work on older browsers.