For deniability, faking data even the owner can’t prove is fake

I was speaking with a colleague yesterday about Loopt, the location-based social network, the rise of location-based services and the incredible privacy challenges they present. I heard the Loopt folks give a talk a few months ago, and I was generally impressed with the measures they’re taking to protect their users’ data.

I particularly enjoyed the problem Loopt faced with respect to abusive spouses: if your spouse is spying on you, it’s not enough to turn off your location services, because then your abusive spouse will know that you’re hiding something. You have to actually be able to lie about your location, in other words Loopt has to let you fake your location data. And they do. And that’s awesome.

It’s just like voting: to be free to vote the way you want to vote, you have to be able to claim that you voted a certain way, even if you voted another way, and that claim has to be believable. In fact, when you think about it, because Loopt offers this “fake my data” feature, there’s no way for you to prove to someone else that you really are where you claim to be, at least not via Loopt. Because, if there were a way to say “okay, really, I’m here, no faking this time,” then there would be no deniability since abusive spouses could simply ask for the extra-no-faking version of the location.

In other words, to truly achieve deniability, you have to take away the user’s ability to certify their own data. That’s not obvious, and it’s interesting that location-based services and voting have this point in common.