I have built a working extension that provides 'window.mozCrypto', which does SHA2 hash, RSA keygen, public key crypto and RSA signature/verification, see: https://addons.mozilla.org/en-US/firefox/addon/domcrypt/ and source: https://github.com/daviddahl/domcrypt I plan on updating the extension once the Draft is more settled (after a first round of commentary & iteration)

CSP will be a huge help in reducing attack vectors. Another thing is the key material being unavailable in the DOM. Current JS libraries do not have the option of making all key references opaque and truly hiding the private and secret key material from the DOM. This spec allows the browser to only ever reference key IDs instead of the actual key material.

You will create keypairs and exchange public keys via a web app. Via the API, you will be able to create digital signatures to help with user verification. This API is not being promoted as a silver bullet for security and privacy, however, when used in conjunction with other browser features like CSP ( http://www.w3.org/TR/CSP/ ) - and I imagine new browser features we still need to figure out (perhaps secure input and reading widgets), we hope to enable more secure web applications. I want to underscore that this API is just the first piece of the pie. Taming and being able to trust the DOM is not going to be easy.

We have Microsoft, Google and Mozilla all deeply involved in the Working Group. I expect this will be a "webkit" patch, and hopefully land in all webkit browsers. Some initial experimentation has been done by me in Gecko in bug 649154: https://bugzilla.mozilla.org/show_bug.cgi?id=649154