Why Your Metadata Is Your Every Move

The metadata that the National Security Agency collects on all calls in the U.S. is not just what's on a phone bill, as the program's supporters have claimed. Your phone bill lists some of the same things the NSA's collecting — numbers dialed, length of all — but does not list the geolocation of each of your calls. It is that final piece of data — where you made your calls — that tells the government everything about your life. "Nobody's listening to the content of people's phone calls,"President Obama said last week. "The only thing taken, as has been correctly expressed, is not content of a conversation, but the information that is generally on your telephone bill," Sen. Dianne Feinstein said on Sunday. "We don't know anything that's in there, we won't search that," said Gen. Keith Alexander, the NSA's director of Cyber Command, at a Senate hearing today. But it doesn't matter. The government doesn't need to listen to your calls. Because it already knows where you are, and that does matter.

In a paper published in Nature's Scientific Reports last year, MIT researchers found that with cell phone call metadata from 1.5 million anonymous people, they could identify a person easily with just four phone calls. As Foreign Policy's Joshua Keatingexplains, they didn't need names, addresses, or phone numbers. They only used time of the call and the closest cell tower.

"We use the analogy of the fingerprint," said [MIT professor 

Yves-Alexandre] de Montjoye in a phone interview today. "In the 1930s, Edmond Locard, one of the first forensic science pioneers, showed that each fingerprint is unique, and you need 12 points to identify it. So here what we did is we took a large-scale database of mobility traces and basically computed the number of points so that 95 percent of people would be unique in the dataset."