On Friday, October 19th, the Pentagon announced that it might turn on "selective deniability" for GPS systems in Afghanistan. If this system were turned on, it would degrade the quality of the GPS signal in Afghanistan. Only special military GPS receivers would be able to receive signals of the standard quality. Some people believe that selective deniability has already been turned on for Afghanistan. Fortunately commercial aircraft flying over the are won't be affected by selective deniability, since the system only limits the accuracy of a receiver to 100 meters, which is barely anything for an airplane.

Of course, this issue is at least slightly controversial. If selective deniability affects areas such as Pakistan and Uzbekistan, the United States' relations with those countries might be at risk. Pakistan is a self-declared ally of the United States, but will they remain happy and unmoved if selective deniability starts limiting their GPS accuracy? It is true that the United States owns most, if not all, of the GPS satellites, and that they can do with these satellites as they wish. However, they can't do whatever they want without making some people angry.

So then, I have a few questions. Most of them have vague answers since selective deniability is a classified technology, but here they are:

  • Q: Will selective deniability affect areas surrounding Afghanistan?
    A: Lt. Jeremy Eggers, a spokesperson at the Air Force base that oversees GPS, says that "[the] region can be very well defined." He will not say if surrounding areas will be affected.
  • Q: If selective deniability does affect countries other than Afghanistan, how will these countries react?
    A: (do you really want to find out)
  • Q: If the military's GPS receivers can bypass selective deniability, isn't it possible for a rogue user to figure out how to mimick a military receiver?
    A: In theory, anything is possible. However, cracking the selective deniability system is probably not going to happen since selective deniability is a classified technology. Few people know exactly how it works, so you wouldn't know where to start to crack the system.
  • Q: Has the selective deniability system been tested? Might it inadvertently interfere with military receivers?
    A: Eggers claims that the United States has previously demonstrated the ability to deny GPS signals when national security has been threatened.

"Pentagon Denies GPS to Taliban" by Delan McCullagh.
Wired News. 20 Oct. 2001

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