Some details from a 1996 paper: http://www.cs.georgetown.edu/~denning/infosec/Grounding.txt -Declan On Mon, Nov 26, 2001 at 11:35:51AM -0500, Trei, Peter wrote:

Curious. 4-5 years ago Denning and another associate (I forget who, it's in the archives :-) tried to market an authentication scheme which purported to authenticate the location of a remote user using GPS.