[lucian1900]

The website or any of the domains it includes JS from can at any time inject some JS into your page, which could maybe replace AES with Base64, or anything else it wished to do.

Native crypto clients don't arbitrarily download code from several domains every time you turn on your app.

[lucian1900]

And I forgot to add, there's no way you can protect against other side-channel attacks like timing attacks. JS as it is today makes it impossible.

[wwwtyro]

What keeps JS from protecting against timing attacks?

Even so, I would argue that it's fair to say that this pushes it along a continuum towards less secure, not that it is "broken".

[wwwtyro]

Yeah, but you have the code. You could see if they were doing that.