  The Automatic Dependent Surveillance-Broadcast (ADS-B) is a surveillance
technology that becomes mandatory in many airspaces. It improves safety,
increases efficiency and reduces air traffic congestion by broadcasting
aircraft navigation data. Yet, ADS-B is vulnerable to spoofing attacks as it
lacks mechanisms to ensure the integrity and authenticity of the data being
supplied. None of the existing cryptographic solutions fully meet the backward
compatibility and bandwidth preservation requirements of the standard. Hence,
we propose the Compatible Authenticated Bandwidth-efficient Broadcast protocol
for ADS-B (CABBA), an improved approach that integrates TESLA, phase-overlay
modulation techniques and certificate-based PKI. As a result, entity
authentication, data origin authentication, and data integrity are the security
services that CABBA offers. To assess compliance with the standard, we designed
an SDR-based implementation of CABBA and performed backward compatibility tests
on commercial and general aviation (GA) ADS-B in receivers. Besides, we
calculated the 1090ES band's activity factor and analyzed the channel occupancy
rate according to ITU-R SM.2256-1 recommendation. Also, we performed a bit
error rate analysis of CABBA messages. The results suggest that CABBA is
backward compatible, does not incur significant communication overhead, and has
an error rate that is acceptable for Eb/No values above 14 dB.
