A practical technique is proposed to authenticate civil GPS signals. The technique combines cryptographic authentication of the GPS navigation message with signal timing authentication based on statistical hypothesis tests to secure civil GPS receivers against spoofing attacks. The notion of GNSS signal authentication is defined in probabilistic terms. Candidate GPS signal authentication schemes are evaluated in terms of effectiveness and practicality leading to a proposal for incorporating digital signatures into the extensible GPS civil navigation (CNAV) message. The proposal is sufficiently detailed to facilitate near-term implementation of security-hardened civil GPS.  

Cite and download the paper:
Wesson, K., M. Rothlisberger, and T. E. Humphreys, “Practical cryptographic civil GPS signal authentication,” NAVIGATION, Journal of the Institute of Navigation, Vol 59, Num 3, 2012, pp 177-193