It's a nice article and generally a sound approach, but reading it has led me to think about something else: imagine an Internet where the data about each user (what would normally be entries in different tables on the servers) is stored, encrypted and authenticated, on the user's computer, as opposed to being stored on the server. Yes, I know, this goes against the 'cloud' principle we see around us and introduces a bunch of issues with syncing this data and it being available everywhere, which is the point of SaaS-like websites. But on the other hand, small websites could use this approach to drastically cut their costs and maintenance work they need to do. Also, a compromise of a server would expose the keys used for encryption, but then the attackers would need another piece of the puzzle, and that's stored on the user's computer.

Don't get me wrong, I'm not advocating this principle or implying it is needed and doable with the current technologies (I don't think we have a way of reliably storing such long-term data within the user's browser), but it's an interesting train of thought. It doesn't obviate the need for the server to store any sensitive information, just some of it. User info, password hashes, credit card numbers, maybe even social graphs depending on the use case, could all be stored this way. There will always be websites for which this doesn't make a lot of sense, but a lot of the other ones, mainly small players, could benefit from this.

It's curious how, when you describe it like that, it sounds that your data is being held hostage by a third party. After all, the server doesn't allow you to see what's in the encrypted opaque blobs, it only allows a controlled set of operations to be done with this data, and the only thing they do is further mutate this opaque blob. But it is no less transparent than the current state of affairs, namely servers keeping the data for themselves.

I'm interested to hear HN's opinion on this, flaws in the approach I've missed, etc.