Where you are as an authentication factor

Not Bad for a Cubicle has posted about location as an authentication factor.

We have also thought about that. The WiKID Strong Authentication token comes in two basic flavors: wired for the Mac, Windows and *nix and wireless for J2ME, Blackberry, Palm, PocketPC and soon, BREW. As the carriers are supposed to be rolling out E911 here in the states, they have some devices that are capable of location-based services. To my knowledge, only BREW phones (Verizon and Alltell in the US) and certainof Nextel's J2ME phones from Motorola allow programmers to access that information.

We would love to create a wireless client that provided three-factor authentication, but I'm not sure if anyone would want it. I would also argue that perhaps it would be more of a deterent than an authentication factor. If someone stole your phone and then tried to guess the PIN - which is stored on the WiKID server - you would know where they were.

In the wired world there are geo-location services based on your IP address, but I don't know how they deal with IP spoofing or a situation where the attacker is logging in from a compromised machine.