On Locational Privacy in the Absence of Anonymous Payments

In this paper we deal with the situation that in certain contexts vendors have no incentive to implement anonymous payments or that existing regulation prevents complete customer anonymity. While the paper discusses the problem also in a general fashion, we use the recharging of electric vehicles using public charging infrastructure as a working example. Here, customers leave rather detailed movement trails, as they authenticate to charge and the whole process is post-paid, i.e., are billed after consumption. In an attempt to enforce transparency and give customers the information necessary to dispute a bill they deem inaccurate, Germany and other European countries require to retain the ID of the energy meter used in each charging process. Similar information is also retained in other applications, where Point of Sales terminals are used. While this happens in the customers’ best interest, this information is a location bound token, which compromises customers’ locational privacy and thus allows for the creation of rather detailed movement profiles. We adapt a carefully chosen group signature scheme to match these legal requirements and show how modern cryptographic methods can reunite the, in this case, conflicting requirements of transparency on the one hand and locational privacy on the other. In our solution, the user’s identity is explicitly known during a transaction, yet the user’s location is concealed, effectively hindering the creation of a movement profile based on financial transactions.