This dissertation was presented to the Faculty of the Graduate School of The University of Texas at Austin in partial fulfillment of the requirements for the degree of

Ph.D. in Electrical Engineering

Civil Global Navigation Satellite System (GNSS) signals are broadcast unencrypted worldwide according to an open-access standard. The virtues of open-access and global availability have made GNSS a huge success. Yet the transparency and predictability of these signals renders them easy to counterfeit, or spoof. During a spoofing attack, a malefactor broadcasts counterfeit GNSS signals that deceive a victim receiver into reporting the spoofer-controlled position or time. Given the extensive integration of civil GNSS into critical national infrastructure and safety-of-life applications, a successful spoofing attack could have serious and significant consequences.

Unlike civil GNSS signals, military GNSS signals employ symmetric-key encryption, which serves as a defense against spoofing attacks and as a barrier to unauthorized access. Despite the effectiveness of the symmetric-key approach, it has significant drawbacks and is impractical for civil applications. First, symmetric-key encryption requires tamper-resistant receivers to protect the secret keys from unauthorized discovery and dissemination. Manufacturing a tamper-resistant receiver increases cost and limits manufacturing to trusted foundries. Second, key management is problematic and burdensome despite the recent introduction of over-the-air keying. Third, even symmetric-key encryption remains somewhat vulnerable to specialized spoofing attacks.

I propose an entirely new approach to navigation and timing security that avoids the shortcomings of the symmetric-key approach while maintaining a high resistance to spoofing. My first contribution is a probabilistic framework that develops necessary components of signal authentication.

Based on this framework, I develop my second and third contributions: an asymmetric-key cryptographic signal authentication technique and a noncryptographic spoofing detection technique, both of which operate without a locally stored secret key. These techniques stand as viable spoofing defenses for civil users and could augment-- or even replace-- current and planned military anti-spoofing measures.

Finally, I offer an in-depth case study of the security vulnerabilities of a modern GNSS-based aviation surveillance technology. I then evaluate possible cryptographic enhancements to the system in the context of the technical and regulatory aviation environment.