mathbabe

The theme of the day yesterday here at the IMA in Minnesota was privacy. There was a talk on privacy and information as well as a discussion later in the afternoon with the participants.

The talk, given by Vitaly Shmatikov, was pretty bad news for anyone who is still hoping to keep private info out of the hands of random internet trolls. Vitaly explained how de-identifying data is a relatively hopeless task, at least if you want to retain useful information in the data, because of the sparseness of most human data.

An example he gave was that the average Netflix user rates 200 films but can be identified on just 4 ratings, at least if you include timestamps. He also pointed out that, even though Netflix doesn’t directly expose its users’ movie preferences, you can infer quite a bit just by looking at how recommendations by Netflix (of the form “people who like House also like Friends”) evolve over time.

And never mind Facebook or other social media, which he explained people can crawl directly and infer the graph structure of; even without any labels for the nodes, which refer to people, one can infer an outrageous amount if you have a separate, labeled graph with overlap on the first.

Conclusion: when people think they’ve de-identified data they haven’t, because other people can collect lots of such data sets, and on top of that some small amount of partial private, identified information about individual users, and piece it together to get creep amounts of stuff.

An example I heard later that day is that someone has figured out how to take pictures of people and give them a large part of their social security number.

The conversation later that day focused more on how companies should protect their client data (through a de-indentifying algorithm), and how for the most part they do absolutely nothing right now. This is perhaps because the problem “isn’t solved” so people don’t see the reason to do something that’s not a perfect solution even though some basic procedures would make it a lot harder. My suspicion is that if they do nothing they are betting they’re more protected from litigation than if they do something that turns out to be too weak. Call me a skeptic but it’s always about litigation.

My contribution to both the talk and the conversation was this: why don’t we stop worrying about data getting out, since it’s kind of a done deal (no data ever disappears and our algorithms are only getting better). Why don’t we assume that all historical information about everyone is out there.

So, besides how to get into my bank account (I haven’t sorted that one out yet, maybe I’ll just have to carry all my money in physical form) I’ll assume everyone knows everything about me, including my DNA.

Then the question becomes, how can we live in a reasonable world given that? How can we, for example, prevent private insurance companies from looking up someone’s DNA or HIV status in order to deny coverage?

This is not an idle concern. As someone pointed out yesterday, 15 years ago nobody would have believed someone who described how much information about the average Facebook user is available now. We have no idea what it will look like in another 15 years.