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

  2. Emerging Threat: Civil GPS Spoofing

  3. Civil GPS Spoofing Testbed at UT Austin Spoofer Defender • Data bit latency defense • Phase trauma monitoring • Dual-frequency tracking

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

  5. 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

  6. 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

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

  8. 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

  9. 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