Spoofing GPS Receiver Clock Offset of Phasor Measurement Units (Technical Report)
We demonstrate the feasibility of a spoofing attack on the GPS receiver of a phasor measurement unit (PMU). We formulate the attack as an optimization problem where the objective is to maximize the difference between the time offset of the PMU’s receiver clock before and after the attack. Since the PMU uses this clock offset to compute a time stamp for its measurements, an error in the receiver clock offset introduces a proportional phase error in the voltage or current phase measurements provided by the PMU, with a phase-wrap of 2 (in practice, the computed maximum receiver clock offset error is never large enough to induce a phase error that requires a phase-wrap of 2). The decision variables in the optimization problem are the satellites’ ephemerides, pseudoranges, and the receiver coordinates. The constraints are cast such that the receiver and satellite positions computed from the solution of the optimization problem will be close to their pre-attack values to avoid detection. We show that the spoofing attack is feasible for any number of visible satellites. Simulation results, in which four and seven satellites are spoofed, are presented to illustrate the effect of the attack on the phase measurement provided by a PMU.
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