A privacy-preserving location-based alert system

Monitoring user location updates has important applications in public safety, national security, etc. However, sensitive information can be derived from movement patterns, so user locations must be disclosed only when some condition is met, for instance in proximity of a disaster area. Searchable encryption techniques provide provable guarantees for privacy, and allow decryption only when the location satisfies some predicate. Nevertheless, they rely on expensive pairing-based cryptography, and direct application to location updates leads to impractical solutions. We propose an efficient technique that leads to significant gains in performance by reducing the amount of pairing operations. We also implement an optimization that reuses results to expensive mathematical operations. Experimental results show that the proposed techniques significantly improve performance compared to the baseline.