Dynamic group size accreditation and group discounts preserving anonymity

Abstract

Group discounts are used by vendors and authorities to encourage certain behaviors. For example, group discounts can be applied to highway tolls to encourage ride sharing, or by museum managers to ensure a minimum number of visitors and plan guided tours more efficiently. We show how group discounts can be offered without forcing customers to surrender their anonymity, as long as customers are equipped with some form of autonomous computing device (e.g. smartphone, tablet or computer). Specifically, we present a protocol suite for privacy-aware group discounts that allows a group of customers to prove how many they are without disclosing their identities. The group does not need to be a stable one, but can have been formed on the fly. Coupled with an anonymous payment system, this makes group discounts compatible with buyer privacy (in this case, buyer anonymity). We present a detailed complexity analysis, we give simulation results, and we report on a pilot implementation.