Comparing Different Diffie-Hellman Key Exchange Flavors for LDACS

Abstract

Growth of civil air traffic worldwide poses a great challenge for the supporting Communication, Navigation and Surveillance (CNS) infrastructure. Analogue systems have to be replaced by digital means to optimize spectrum efficiency and automation is becoming much more important to be able to handle the amount of participants in the air traffic system. As safety and security are strongly intertwined in aviation, cybersecurity is one key enabler for digitalization in civil aviation. As such we investigate mutual authentication and key agreement methods for the digital aeronautical ground-based communications system L-band Digital Aeronautical Communication System (LDACS). Thereby, we compare the suitability of three different Diffie-Hellmann (DH) key exchange flavors used in a modified version of the Station-To-Station (STS) protocol, for digital aeronautical communication in terms of latency and security data overhead. We conclude, the STS protocol based on a central Public Key Infrastructure (PKI) trust solution with Supersingular Isogeny Diffie-Hellman (SIDH) for post-quantum security to be best suited for long term security. However, due to the smaller key sizes, Elliptic Curve Diffie-Hellman (ECDH) is the more resource efficient candidate and may play a role in low resource authentication scenarios for LDACS.

LDACS Flight Trials: Demonstration and Performance Analysis of the Future Aeronautical Communications System

“…A duration for the key exchange procedure of 283.74 ms for the 95th percentile was measured. This goes in line with the theoretical and simulation-based evaluations published in [37], [38]. An in-depth analysis of the security measures employed in the campaign for data broadcast over LDACS can be found in [31].…”

Flight Trial Demonstration of Secure GBAS via the L-band Digital Aeronautical Communications System (LDACS)

“…In the experiment public keys and certificates of the ground-station and aircraft-station were bilaterally exchange via LDACS. In an operational deployment of LDACS the distribution of public keys and certificates will likely be realized via an LDACS specific public key infrastructure, as described in [14,15,16,17]. Knowing Alice's public key, Bob can verify the authenticity of the TESLA parameters and start buffering messages sent by Alice until he receives the correct key to verify their authenticity.…”

A Secure Cell-Attachment Procedure of LDACS

“…Previous security analysis of LDACS identified requirements of the cell-attachment procedure [10], [11], [13], [15]: Mutual Authentication, Perfect Forward Secrecy and Secure Key Establishment in event of an adversary or compromise of long-term keys. This requires the key establishment method to be based on ephemeral keys, where both parties contribute to the final shared secrets and the inputs are chosen freshly for every protocol run.…”

“…All these documents define access control, options to protect user data in transit on link layer, and protection of the control plane of the radio access technology, as a requirement to be incorporated into the Air Traffic Network (ATN)/IP-Protocol Suite (IPS) network. In previous works, threat-and risk analysis of LDACS were conducted [9], [10], a draft for an LDACS cybersecurity architecture introduced [11], [12], algorithms proposed [13], [14] and the security of the Station to Station (STS)-based Mutual Authentication and Key Establishment (MAKE) procedure of LDACS formally verified [15]. Thereby, the low data rates of aeronautical systems, which originates from low limited dedicated spectrum for civil aviation and resulting 500 kHz channel sizes for LDACS [16], is respected.…”

“…Thereby, the low data rates of aeronautical systems, which originates from low limited dedicated spectrum for civil aviation and resulting 500 kHz channel sizes for LDACS [16], is respected. Hence, the rationale for the cell-attachment procedure is to reduce the amount of security message exchanges between GS and AS and the overall amount of the LDACS security overhead [11], [13].…”