Comment Re:Time for GPS over SSL - GPS^2? (Score 3, Informative) 41
GPS is not ethernet, attempting to use ethernet based techniques for GPS is naive.
As a simple illustration GPS is a one way broadcast, the receiver has no return channel. This means that there can't be any kind of handshake process, and you are completely vulnerable to a replay attack. As a very basic attack a spoofer could transmit low level noise across the frequency preventing the normal GPS signal from being received. They could listen to the real signal, and then retransmit it at significantly higher power levels a fraction of a second later. The delay would significantly impact the pseudorange for that signal and the computed position, time shifting multiple signals would allow you to alter the position in a predictable way.