Differentially Private Billing with Rebates
A number of established and novel business models are based on fine grained billing, including pay-per-view, mobile messaging, voice calls, pay-as-you-drive insurance, smart metering for utility provision, private computing clouds and hosted services. These models apply fine-grained tariffs dependent on time-of-use or place of-use to readings to compute a bill. The authors extend previously proposed billing protocols to strengthen their privacy in two key ways. First, they study the monetary amount a customer should add to their bill in order to provably hide their activities, within the differential privacy frame-work. Second, they propose a cryptographic protocol for oblivious billing that ensures any additional expenditure, aimed at protecting privacy, can be tracked and reclaimed in the future, thus minimising its cost.