Assisted NMA with Secure Time Synchronization on Android Smartphones

Cillian O'Driscoll, Ignacio Fernandez-Hernandez, Jon Winkel, Tom Willems, Aleix Galan-Figueras

Abstract:	In previous work we have presented a proof of concept implementation of the Assisted Navigation Message Authentication (ANMA) concept on Android smartphones. In this work we extend upon that proof of concept by adding a secure time synchronization via the Network Time Security (NTS) protocol. A secure bound on time is essential for the correct implementation of Open Service Navigation Message Authentication (OSNMA), which motivates our inclusion of this element in the proof of concept. However, in this paper we demonstrate that such a secure time bound provides benefits even if the NMA component is not used. We demonstrate through field trials that a bound on time typically better than ±75 ms can be achieved using NTS over standard telecoms networks (4G/5G). In the absence of NMA this gives a potential attacker a window of approximately 150 ms in which to effect an attack. The additional benefit of ANMA is that it reduces this window to approximately 20 ms. Some issues with navigation message decoding are also discussed.
Published in:	Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025) September 8 - 12, 2025 Hilton Baltimore Inner Harbor Baltimore, Maryland
Pages:	1132 - 1143
Cite this article:	O'Driscoll, Cillian, Fernandez-Hernandez, Ignacio, Winkel, Jon, Willems, Tom, Galan-Figueras, Aleix, "Assisted NMA with Secure Time Synchronization on Android Smartphones," Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025), Baltimore, Maryland, September 2025, pp. 1132-1143. https://doi.org/10.33012/2025.20474
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