A method for detecting the spoofing of civilian GPS signals has been implemented and successfully tested in a real-time system. GPS signal spoofing is an attack method whereby a third party transmits a signal that appears authentic but induces the receiver under attack to compute an erroneous navigation solution, time, or both. The detection system described herein provides a defense against such attacks. It makes use of correlations between the unknown encrypted GPS L1 P(Y) code signals from two narrow-band civilian receivers to verify the presence or absence of spoofing. One of these receivers is assumed to be at a secure location that is not subject to spoofing. The other receiver is the potential spoofing victim for which the present developments constitute a defense. Successful detection results are presented using a reference receiver in Ithaca, New York, a victim receiver in Austin, Texas, and a spoofer in Austin, Texas.

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B.W. O'Hanlon, M.L. Psiaki, J.A. Bhatti, D.P. Shepard, T.E. Humphreys, "Real-Time GPS Spoofing Detection via Correlation of Encrypted Signals," NAVIGATION, Vol 60, Issue 4, 267-278, 2013.