Bruce Schneier’s Crypto-Gram points to some impressive work done by researchers at the University of Washington showing how Apple’s Nike + iPod kit can be used to track people. The kit consists of a transmitter that you put in your shoe and a receiver you plug into your iPod. The transmitter wakes up whenever it gets shaken and sends out pedometer info every second, and the receiver then uses that info to give voice and visual feedback on your pace and how far you’ve run. The UW team discovered that each transmitter sends out a unique ID so the receivers can distinguish among several in the area, and then built several PDA-sized units to listen for IDs and log the data either to flash memory or retransmit it over Wi-fi or SMS. They also built software that would trigger a USB camera whenever a particular ID went by, and wrote a visualization tool that shows either historical or real-time overlays of sensor IDs and/or pictures taken on top of Google Maps. Details are in their paper, and they also have a video.
The threat models they lay out aren’t government surveillance so much as jealous/ex-boyfriends and stalkers, and to some extent professional thieves and muggers, unethical organizations tracking their members (or their competition’s members), and stores tracking their customers. Except for muggers (which just involves detecting whether a passing jogger is likely to have an iPod or other cool gadgets on them), all the scenarios they discuss involve the use of a network of their relatively cheap sensors, each one adding a single location to the overall surveillance network. A stalker would place trackers at strategic locations, then wait for them to phone home with the unique IDs they see. To link a a unique ID with a particular person he just has to get close to his target (or for that matter just watch her jog by) and then note the ID that’s being broadcast. Or he can leave one tracker in the bushes by his target’s front door and note what ID it picks up (he gets when she comes and goes that way too). And since consumers are encouraged to “just drop the sensor in their Nike+ shoes and forget about it” the trackers will work even when the target isn’t actually jogging or using the device.
The work is impressive, but I feel like by focusing on the Nike + iPod design it’s pointing to the smoke instead of the fire. Yes, Apple probably could have designed their system to make this sort of tracking more difficult. Ditto the RFID chips in smart cards, passports, highway toll-payment boxes, quick-payment key fobs and consumer products, not to mention Bluetooth devices and cellphones. But the main technology trend that’s making this sort of tracking possible, I would argue, is not the plethora of remotely-readable unique IDs we carry everywhere we go so much as the small, cheap hardware that even a moderately technical attacker can turn into his very own sensor network. RFID and transmitters are a ready-made “fingerprint” that such sensor networks can read easily, but as machine vision and pattern recognition technology improves there will be an increasing number of features will uniquely identify you to a sensor network, including minor differences in hardware you carry, how you walk or what you look like. This is not to say we shouldn’t encourage companies to make tracking by RFID harder to do, but I think it’s at best going to buy us 5-10 years before you’ll be able to buy your own automatic person-tracking sensor network at any online spy-shop. We’d better be thinking now about what kind of social and legal systems we’ll want once that day comes.