My opinion of various GPS vulnerabilities at the unclass level:
1. Shoot Down
A few numbers should suffice:
GPS orbital altitude:
20,200km (in Medium Earth Orbit, along with GLONASS and Galileo)
Altitude of weather satellite shot down by China:
850km
The technology demonstrated by China only threatens satellites in Low Earth Orbit (up to 2000km, e.g. reconnaissance satellites). Furthermore, GPS has significant redundancy, with (currently) 30 satellites in orbit, so would withstand a degree of attrition.
2. Jamming
As already stated above, GPS is now operating on a greater range of frequencies. The bandwidth of the military frequencies makes jamming a lot harder. Not willing to say anything else!
3. Spoofing (vs airborne platforms only)
Every course I've been on that covers GPS gets round to the subject of spoofing. I don't claim to be an expert on the subject (and a little bit of knowledge can be a dangerous thing
) but you don't need to be a techno-whiz to understand the following:
a. Spoofing Individual Receivers
The required process would be to:
a) Determine the current position of the receiver you want to spoof.
b) Calculate what signal that receiver will be getting from each GPS satellite.
c) Calculate what signal the receiver needs to see from each satellite in order to achieve the desired spoofing.
d) Generate and transmit those signals, complete with the appropriate P(Y) and M-code encryptions.
Only the targeted receiver would actually be spoofed. The "bespoke" signals would make no sense to any other receiver in the area and would be rejected.
b. Wide-area Spoofing
This time, the spoofing needs to apply "credible" modifications to the GPS signal, appearing "robust" to all possible users in an area. These modifications would have to be different in different geographical areas - spoofing 100m to the West requires different signals in Kabul and Kandahar, for example.
c. Kalman-filtered GPS / LINS (and TERPROM)
As already observed by a previous poster, the integration of GPS and LINS in one box is what's really at the heart of the revolution in navigation (not least the re-titling of Navigators as WSOs!). Short-term and localised disturbance to GPS has no effect on navigational accuracy of these systems. Longer-term disturbance may well cause degradation. However, the wannabe GPS spoofer now has to tailor his spoofing to sneak beneath the threshold of the Kalman filter lurking within all these boxes. Otherwise, Mr. Kalman will ignore the GPS inputs and warn the system that something is amiss. In a cruise missile, this might prompt reversion to TERPROM navigation. In a UAV or manned aircraft, it would prompt a crew to carry out a reversionary attack (laser-guided, perhaps) or take a navigational fix using traditional methods. Or, if the LINS is good enough, continue navigating inertially until clear of the spoofing. Platforms such as F-15 can already target inertially-guided munitions using synthetic aperture radar pictures.
Spoofing
(vs air platforms) summary - virtually impossible to achieve against a single receiver, let alone across a wide area. Even if it could be achieved, largely pointless, thanks to modern kit. The story might be a bit different against ground-based, slow moving receivers, but someone else might be able to provide more detail.
Controlled Radiation Pattern Antennae (CRPA) provide a further robust antidote to both jamming and spoofing. Google can provide more details for you and then I don't have to tread a fine line of classification.
Anyway, in summary, I don't feel like I need to dust down the old sextant or Dalton computer just yet. Perhaps the General's statement is just designed to keep would-be jammers and spoofers spending money on developing ineffective countermeasures...