[tptacek]

This is a bad idea. The value of encrypting-before-uploading is that you don't have to trust the server. But you implicitly trust the server when you except encryption code for it.

This fact usually sets off a day-long thread about the things you can do trust the code (read it! hash it! deliver it via SSL from a trusted CDN!), but these arguments always miss the fundamental point that you are trusting code that is (a) delivered over the network (b) at least partly by a server you don't trust (c) in an environment that binds arbitrary evals to every element of the DOM (d) using a language that allows you to override and booby-trap almost every operation. It's just not going to work.

SJCL is awesome. Figuring out how to efficiently implement crypto in Javascript is a really valuable research project. But right now, you shouldn't be using this outside of serverside Javascript or custom clients.

(And, really, if you have to type the letters A-E-S or H-M-A-C, you're doing it wrong anyways.)