You seem to know a lot about this and it always interested me.
How does current GPS prevent from spoofing. My understanding is that only military GPS signals are encrypted. If so, how strong is the encryption? What type it is?
How does current GPS prevent from spoofing. My understanding is that only military GPS signals are encrypted. If so, how strong is the encryption? What type it is?
To be able to spoof GPS, you need to be able to duplicate the ranging code for a given satellite. This is easy for civilian GPS, where the code repeats ~1000 times/sec and the details are public; much harder for military code where it repeats 1 time/week and the parameters are secret.
You can still jam either one, though, just by overwhelming appropriate frequencies with noise. This is what the spot beam in newer satellites is for -- getting more power to areas of conflict to make the signal harder to jam.
A standard block cipher running in CTR mode would provide the same functionality. So I don't think its wrong to say that the signal is encrypted.
There are a few anti-spoofing defenses available right now, but they are either expensive or ineffective. If the target has a high-quality inertial navigation system or clocks, then the slew rate available to the attacker is greatly reduced. There are also some defenses related to DGPS, but they require a separate base station and communication side-channel to execute.
Right now, the hardware cost to deploy an advanced attack like that is relatively cheap, and subject to Moore's Law. A GNU Radio USRP could do it right now, for example. The hardware cost to defend against it is expensive, and not getting any better. Changing the signal structure to incorporate cryptographically strong authentication is the only solution I can see to swing the pendulum back the other way.