Apple briefly announced “differential privacy” at this year’s WWDC keynote, but didn’t go into details as to exactly what that means. Cryptographer Matthew Green isn’t sure what Apple means either, but he is familiar with the concept of differential privacy and explains the basics and how Apple could be implementing it.
To make features like Spotlight and QuickType more useful to you, Apple needs to collect data from your iPhone usage, but it doesn’t want to violate your privacy. Unfortunately, even if Apple collects data anonymously, it could still be analyzed later to identify you. In effect, differential privacy injects a certain amount of phony data into the system, sacrificing a bit of accuracy for more privacy. We’re curious to learn more about how this works, too, and how effective it actually is.