uCentive: An Efficient, Anonymous and Unlinkable Incentives Scheme

Incentives systems are widely adopted to encourage user actions or contributions that benefit a service provider or a community. In exchange for their actions, users receive incentive points that can be used to obtain benefits or reputation. However, these systems require users to have a central account associated with all their activities. This approach allows providers to collect vast amounts of users´ private information, even if pseudonyms are used. In this paper, we present uCentive, a flexible and efficient incentives scheme that allows users to earn and redeem incentives (uCents) that cannot be linked to their identities or actions. In addition, users can prove, if requested, ownership of their incentives without breaking unlinkability guarantees. uCentive also offers perfect forward unlinkability -- even if the user´s secrets are compromised, redeemed uCents cannot be linked together or to the user´s identity. Even though our scheme relies on heavy cryptography, experimental evaluation shows that it is adequate for mobile devices such as smartphones. We have also made our uCentive library and prototype apps publicly available for further assessment. In short, we provide a practical privacy-preserving incentives scheme that can eliminate users´ growing privacy concerns when using such systems.