It's SJCL, a pretty popular JS crypto library.

https://crypto.stanford.edu/sjcl/

Nice! Thanks for this.

Having a file encrpyt to an HTML file is pretty interesting, something I've never considered before. Very portable.

I really like the portability and accessibility of HTML files, especially as very thin local apps.

Here is one of my projects playing with that concept: https://github.com/srpeck/markdowned