Some slight misunderstandings, I fear?
The US GPS system sends C/A and P code signals. C/A ('coarse acquisition) is the 'civilian' version and used to include Selective Availability (SA) before Clinton ordered it to be switched off. SA applied random time error signals and vehicle ephemeris values to reduce system accuracy to levels which would not pose a serious threat if misused by terrorists.
But with Differential GPS improving C/A accuracy, SA became rather unnecessary. WAAS will improve C/A accuracy even further in the USA and EGNOS will do the same (one of these days
) in €uroland. Most modern Garmin systems include WAAS/EGNOS compatability.
Military systems use far more accurate P-code ('precision') signals which use faster digital code sequences. Originally it was thought that the P-code position information would be 10 x as accurate as C/A; however, C/A was so accurate that SA was needed to degrade it when necessary.
It would be possible for a civilian user to use some clever processing to use P-code signals by detecting the C/A 'handover word', accessing the L1 and L2 frequencies and using the P-codes. So the P-code is also encrypyted; it is then know as Y-code. Unless cryptovariables are loaded into a mil spec GPS receiver, it will only use C/A positioning.