Is the problem with the JS language itself? I don't know. I do know that other dynamic languages are trusted to perform crypto (e.g. Python). The fact that any

Is the problem with the JS language itself? I don't know. I do know that other dynamic languages are trusted to perform crypto (e.g. Python). The fact that any dynamic language is trusted leads me to believe JS as a language may be fine. or with certain JS runtimes? Yes, each runtime must be analyzed by a crypto expert to uncover e.g. timing attack vulnerabilities, etc. or with just the idea of running a program inside a web browser to do crypto? Yes, implementing crypto within a webpage is a bad idea for many reasons. The first is that you must ultimately trust the browser itself, as well as its updater program. Second, you must trust every browser extension, since any extension can arbitrarily modify the page, and hence the javascript. (e.g. Reddit Enhancement Suite does this.) Since every extension can be updated at any time, you can't really trust any extension. Third, the javascript can be compromised in many other ways (e.g. XSS attack, etc). Fourth, crypto itself is extremely difficult to implement correctly, and it's easy to trick yourself into adding flaws while implementing it. For these and other reasons, browser-based crypto can't ever be trusted. Not yet, and not until the above concerns are no longer relevant.