Comments on "A Privacy-Preserving Online Ride-Hailing System Without Involving a Third Trusted Server"

Recently, Xie et al. (IEEE Transactions on Information Forensics and Security, vol. 16, pp. 3068-3081, 2021) proposed a privacy-preserving Online Ride-Hailing (ORH) protocol that does not make use of a trusted third-party server. The primary goal of such privacy-preserving ORH protocols is to ensure the privacy of riders' and drivers' location data w.r.t. the ORH Service Provider (SP). In this note, we demonstrate a passive attack by the SP in the protocol of Xie et al. that enables it to completely recover the location of the rider as well as that of the responding drivers in each and every ride request query.