Everything We Know About How the NSA Tracks People's Physical Location

With Monday's new revelation, we can see the NSA's two-pronged system for finding out where people are.
The NSA can find you, in part, through cell towers ( Gary Lerude / Flickr )

Glenn Greenwald is back reporting about the NSA, now with Pierre Omidyar’s news organization FirstLook and its introductory publication, The Intercept. Writing with national security reporter Jeremy Scahill, his first article covers how the NSA helps target individuals for assassination by drone.

Leaving aside the extensive political implications of the story, the article and the NSA source documents reveal additional information about how the agency’s programs work. From this and other articles, we can now piece together how the NSA tracks individuals in the real world through their actions in cyberspace.

Its techniques to locate someone based on their electronic activities are straightforward, although they require an enormous capability to monitor data networks. One set of techniques involves the cell phone network, and the other the Internet.

Tracking Locations With Cell Towers

Every cell-phone network knows the approximate location of all phones capable of receiving calls. This is necessary to make the system work; if the system doesn’t know what cell you’re in, it isn’t able to route calls to your phone. We already know that the NSA conducts physical surveillance on a massive scale using this technique.

By triangulating location information from different cell phone towers, cell phone providers can geolocate phones more accurately. This is often done to direct emergency services to a particular person, such as someone who has made a 911 call. The NSA can get this data either by network eavesdropping with the cooperation of the carrier, or by intercepting communications between the cell phones and the towers. A previously released a Top Secret NSA document says this: “GSM Cell Towers can be used as a physical-geolocation point in relation to a GSM handset of interest.”

This technique becomes even more powerful if you can employ a drone. Greenwald and Scahill write:

The agency also equips drones and other aircraft with devices known as “virtual base-tower transceivers”—creating, in effect, a fake cell phone tower that can force a targeted person’s device to lock onto the NSA’s receiver without their knowledge.

The drone can do this multiple times as it flies around the area, measuring the signal strength—and inferring distance—each time. Again from the Intercept article:

The NSA geolocation system used by JSOC is known by the code name GILGAMESH. Under the program, a specially constructed device is attached to the drone. As the drone circles, the device locates the SIM card or handset that the military believes is used by the target.

The Top Secret source document associated with the Intercept story says:

As part of the GILGAMESH (PREDATOR-based active geolocation) effort, this team used some advanced mathematics to develop a new geolocation algorithm intended for operational use on unmanned aerial vehicle (UAV) flights.

This is at least part of that advanced mathematics.

None of this works if the target turns his phone off or exchanges SMS cards often with his colleagues, which Greenwald and Scahill write is routine. It won’t work in much of Yemen, which isn’t on any cell phone network. Because of this, the NSA also tracks people based on their actions on the Internet.

Presented by

Bruce Schneier is a correspondent for The Atlantic and the chief technology officer of Co3 Systems, a computer-security firm. A security and technology specialist, his latest book is Liars and Outliers: Enabling the Trust That Society Needs to Thrive.

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