Internet probe can track you down to within 690 metres

Eugen Leitl eugen at
Fri Apr 8 06:49:18 PDT 2011

Internet probe can track you down to within 690 metres

15:06 05 April 2011 by Jacob Aron

Online adverts could soon start stalking you. A new way of working out where
you are by looking at your internet connection could pin down your current
location to within a few hundred metres.

Similar techniques are already in use, but they are much less accurate. Every
computer connected to the web has an internet protocol (IP) address, but
there is no simple way to map this to a physical location. The current best
system can be out by as much as 35 kilometres.

Now, Yong Wang, a computer scientist at the University of Electronic Science
and Technology of China in Chengdu, and colleagues at Northwestern University
in Evanston, Illinois, have used businesses and universities as landmarks to
achieve much higher accuracy.

These organisations often host their websites on servers kept on their
premises, meaning the servers' IP addresses are tied to their physical
location. Wang's team used Google Maps to find both the web and physical
addresses of such organisations, providing them with around 76,000 landmarks.
By comparison, most other geolocation methods only use a few hundred
landmarks specifically set up for the purpose.  

Closing in

The new method zooms in through three stages to locate a target computer. The
first stage measures the time it takes to send a data packet to the target
and converts it into a distance b a common geolocation technique that narrows
the target's possible location to a radius of around 200 kilometres.

Wang and colleagues then send data packets to the known Google Maps landmark
servers in this large area to find which routers they pass through. When a
landmark machine and the target computer have shared a router, the
researchers can compare how long a packet takes to reach each machine from
the router; converted into an estimate of distance, this time difference
narrows the search down further. "We shrink the size of the area where the
target potentially is," explains Wang.

Finally, they repeat the landmark search at this more fine-grained level:
comparing delay times once more, they establish which landmark server is
closest to the target. The result can never be entirely accurate, but it's
much better than trying to determine a location by converting the initial
delay into a distance or the next best IP-based method. On average their
method gets to within 690 metres of the target and can be as close as 100
metres b good enough to identify the target computer's location to within a
few streets.  

Client independent

That kind of accuracy normally requires people to deliberately disclose their
location, but Wang's method works without the user's permission. "This is a
client-independent method," as he puts it. "The client does not need to
approve anything."

You can avoid any geolocation method by routing traffic through a proxy
server, which makes you appear to be elsewhere. Wang can't get around this,
but says he can detect proxies and so he can at least return a null result
rather than a false positive.

Although Wang's method could potentially allow adverts to target a certain
street, advertisers may prefer to retain broader messages. "The majority of
brands wouldn't necessarily want to go to that much granularity," says Jack
Wallington at the Internet Advertising Bureau in London. He says the method
could be useful in certain situations, however, such as targeting hungry
office workers with vouchers for nearby takeaway food outlets.

Wang presented the research last week at the Usenix Symposium on Networked
Systems Design and Implementation in Boston.

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