Authenticating Aviation Augmentation System Broadcasts

S. Lo, P. Enge

Abstract:	An important function of augmentation systems for Global Navigation Satellite Systems (GNSS) is providing information need to guarantee the integrity of GNSS derived position, navigation and time (PNT) outputs. This mission is the primary purpose of spaced based and ground based augmentation system - SBAS and GBAS, respectively. These systems are designed to serve aviation navigation and landing by providing information needed to assure safe use of GNSS. Thus, information integrity is fundamental to these augmentation systems. One component of information integrity is the ability to authenticate the source of the data. While this assurance is currently not built into these systems, it may be possible to overlay authentication capability. Traditional data authentication techniques can be used to provide source assurance. However, augmentation systems have requirements that differ from the channels for which these techniques were designed. In particular, the data is more time sensitive and the bandwidth is much more limited. Additionally, user and system equipment are designed for decades of service with little to no upgrades. As a result, aviation seeks data authentication that is 1) fast, 2) robust to message loss, 3) not resource intensive 4) self contained and 5) robust to future attacks. Traditional data authentication techniques must be adapted to achieve these targets with limited bandwidth and limited two way communications. Meeting these desired qualities may be difficult given design constraints imposed by low bandwidth, avionics, and airspace infrastructure. However, the characteristics of augmentation systems and its operations may also aid the design. These attributes limit the types of attacks that are feasible against the system as well as provide means to cross check information. The paper starts by examining the reasons for and desirable features of authentication on aviation augmentation systems. Next, it considers basic cryptography and traditional data authentication techniques suitable for the aviation broadcast environment. Protocols based on asymmetric and symmetric key are discussed. Additionally, key strength and related issues are looked at. It then examines the important consideration of key distribution as this may be a major hurdle to adoption. This paper presents a key distribution protocol that utilizes the operation of the aircraft and air traffic to aid in key verification. The last section of the paper presents some case study designs for SBAS and GBAS. These designs are not meant to be proposal but rather to give some idea about feasibility and data requirement.
Published in:	Proceedings of IEEE/ION PLANS 2010 May 4 - 6, 2010 Renaissance Esmeralda Resort & Spa Indian Wells, CA
Pages:	708 - 717
Cite this article:	Lo, S., Enge, P., "Authenticating Aviation Augmentation System Broadcasts," Proceedings of IEEE/ION PLANS 2010, Indian Wells, CA, May 2010, pp. 708-717. https://doi.org/10.1109/PLANS.2010.5507223
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