<p>The low-altitude transport system is a revolutionary transportation paradigm by unlocking the vast untapped airspace for autonomous unmanned aerial vehicle (UAV) operations beyond congested ground networks. However, the widespread exploitation of the low-altitude transport system faces numerous challenges, especially in terms of privacy and security. In particular, unregistered UAVs may impersonate legitimate UAVs to access the airspace. Meanwhile, registered UAVs may conduct illegal flights beyond their authorized airways, posing severe risks to public safety and property. With the above challenges, we propose a privacy-preserving airways authentication (PAA) scheme that achieves both identity and airway legitimacy authentication, which combines an efficient laconic private-set intersection (PSI) protocol with a Bloom filter. To authenticate the legitimacy of airways, we innovatively insert the cubic units denoting the restricted airspace to decrease the overhead brought by false positives in the Bloom filter. Comprehensive security analysis shows that the PAA scheme achieves the goal of confidentiality under a simulation-based real/ideal world model. Moreover, we compare the PAA scheme with baseline schemes in terms of communication overheads and computational costs. Evaluation results show that our scheme outperforms the baseline schemes, and our scheme is feasible under the large-scale UAV flight scenario.</p>