What is differential privacy?

To make a long story short, it sounds like Apple is going to be collecting a lot more data from your phone. They're mainly doing this to make their services better, not to collect individual users' usage habits. To guarantee this, Apple intends to apply sophisticated statistical techniques to ensure that this aggregate data - the statistical functions it computes over all your information - don't leak your individual contributions. In principle this sounds pretty good. But of course, the devil is always in the details.While we don't have those details, this seems like a good time to at least talk a bit about what Differential Privacy is, how it can be achieved, and what it could mean for Apple - and for your iPhone.