Challenges of Practical Civil GNSS Security Todd Humphreys, UT Austin Civil Navigation and Timing Security Splinter Meeting |Portland, Oregon | September 23, 2010

Emerging Threat: Civil GPS Spoofing

Civil GPS Spoofing Testbed at UT Austin  Data bit latency defense  Phase trauma monitoring  Dual-frequency tracking SpooferDefender

Video Demonstration of Spoofing Attack (not embedded; see posted video)

Thoughts on the Way Forward for Civil GNSS Authentication  More signals means more inherent security, but probably insufficient  Some civil cryptographic authentication scheme is likely required  “Signal definition inertia is enormous” – Tom Stansell  Navigation message authentication (NMA) appears to be best, practical option (advocated by Logan Scott in 2003, others since)  Goal of cryptographic authentication: force adversary to use directional antennas in a replay attack  Preliminary evaluation of NMA for L2C suggests optimism, but strategy is not water-tight  Cryptography is the easy part

Hard Part: Defend Against Security Code Replay Attack >500 MHz FPGAs enable near-zero-delay replay attack Soft W-bit Estimation Hard W-bit Estimation

Effect on Target Receiver C/No Soft W-bit Estimation Hard W-bit Estimation

Spoofing Detection as a Hypothesis Testing Problem (Soft W Estimation) Spoofing detection depends critically on good estimates of nominal (C/No)s and (C/No)r

Final Observations  Must defend against following spoofing strategy: (1) soften up target with low-grade jamming, (2) begin soft- estimate replay attack, (3) transition to hard-estimate replay attack  A J/N meter is indispensable in spoofing detection to eliminate the possibility that the receiver’s estimate of its own nominal C/No (in the absence of spoofing) has been altered  Solar radio bursts, unintentional/intentional jamming will tend to trigger spoofing alarms  Spoofing detection is challenging for dynamic platforms because of the volatility in the nominal C/No