[jhayward]

Now please explain, in terms of how GPS receivers operate, how that information helps you defeat spoofing.

[pps43]

GPS receiver determines its position by measuring the distances to GPS satellites. Those distances are calculated from time delays. To get the delays, the receiver should know the exact time. Its own clock is not stable enough to do it, so our receiver has to determine exact time by monitoring one more satellite than is strictly necessary, and calculating the time from that.

Now if this "exact" time suddenly jumps (compared to internal clock), it probably means that the signal is not coming directly from the satellites, but relayed from Vnukovo.