Storing Passwords in HTML5 LocalStorage

I need to store passwords in the HTML5 LocalStorage (No, I 开发者_Go百科can't use hashes and I can't ask the user to type his password).

What is the most secure way to do this? I understand that this can never be really safe, but I'm just looking to secure this as much as possible.

Can you do encryption in JavaScript? If yes, what is the best encryption algorithm for this task?

Thank you.

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The closure library has a set of encoding algorithms in Javascript, maybe one of those can help: http://code.google.com/p/closure-library/source/browse/#svn%2Ftrunk%2Fclosure%2Fgoog%2Fcrypt

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I had the same problem with my (ancient) N97 web-runtime application. I used JavaScrypt which worked fine for me.