Progress in Cryptology – INDOCRYPT 2021

In a typical ride-hailing service, the service provider (RS) matches customer (RC) with closest vehicle (RV) registered to this service. TRACE is an efficient privacy-preserving proposed by Wang et al. in 2018. uses masking along other cryptographic techniques ensure and accurate ride-matching. The RS masked location information match RCs RVs within quadrant without obtaining their exact locations, thus ensuring privacy. work, we disprove privacy claims showing following: a) can identify secret spatial division maintained (this reveals about density of region potential trade secrets), b) locations violates privacy). Prior exchanging encrypted messages protocol, each entity masks plaintext message unknown others. Our attack allows entities recover from value exploiting shared randomness used across different messages, that eventually leads system linear equations plaintexts. This holds even when all participating are honest-but-curious. We implement our demonstrate its efficiency high success rate. For security parameters recommended for TRACE, RV less than minute, second on commodity laptop.