BBA+

Abstract

Black-box accumulation (BBA) has recently been introduced as a building-block for a variety of user-centric protocols such as loyalty, refund, and incentive systems. Loosely speaking, this building block may be viewed as a cryptographic "piggy bank" that allows a user to collect points (aka incentives, coins, etc.) in an anonymous and unlinkable way. A piggy bank may be "robbed" at some point by a user, letting her spend the collected points, thereby only revealing the total amount inside the piggy bank and its unique serial number.