It's a fundamental problem with browser crypto. The attack surface of a crypto routine running in a webpage is really large. There are a lot of places where inf

It's a fundamental problem with browser crypto. The attack surface of a crypto routine running in a webpage is really large. There are a lot of places where information could leak in or out, such as timing attacks. If an XSS attack on a webpage succeeds, then a large number of different attack opportunities could exist on browser crypto loaded from that page. Users might also have browser extensions which have the ability to inject into or steal from the web page. The number of things to worry about inside a browser is just way too high to really even consider using it to secure anything. The crypto would have to be built in to the browser at the very least.