ABLA: Asymmetric Backscatter Lightweight Attestation - A Lightweight Attestation Protocol for Radar and Backscatter Transponder Links

Abstract

Augmenting existing surveillance systems with complementary devices that extend their capabilities introduces new challenges. Such an auxiliary device typically shares the hostile environment of the system it serves, so it must be authenticated and shown to be running uncompromised firmware before its reports can be trusted. Remote attestation addresses this: a verifier checks a prover’s integrity, e.g. through a hash of the software running on the device. This thesis, carried out in collaboration with Saab AB, examines one such case: the integration of a device intended to complement a rotating radar. The device is networked and assumed to be exposed to adversaries capable of eavesdropping, replay, spoofing, jamming, and physical capture. The communication link is, however, severely asymmetric: the downlink carries only tens of bits per second, while the backscatter uplink operates at a few hundred. We propose ABLA: Asymmetric Backscatter Lightweight Attestation, a five-phase remote attestation protocol designed for this setting. The protocol uses only symmetric primitives on the device side and combines challenge–response attestation with a radar-based proximity check step that reuses the radar’s existing range and bearing measurements to detect relay attacks and physical displacement at no additional cryptographic cost. ABLA’s cryptographic security is analyzed symbolically in the Tamarin prover; the model covers the cryptographic core of Phases 3 and 4 only, establishing key secrecy, message authentication, verifier-commit uniqueness per session tuple, and a minimal attestation-soundness property under a Dolev–Yao adversary. The protocol’s operational behavior is evaluated through discrete-event simulation in OMNeT++ for deployments of up to 32 transponders.