Accountable privacy supporting services

As privacy concerns among consumers rise, service providers increasingly want to provide services that support privacy enhancing technologies. At the same time, online service providers must be able to protectthemselves against misbehaving users. For instance, users that do not paytheir bill must be held accountable for their behavior. This tension betweenprivacy and accountability is fundamental, however a tradeoff is not alwaysrequired. In this article we propose the concept of a time capsule, that is, a verifiable encryption with timed and revocable decryptability. The timecapsule together with its related protocols offer support of privacy whileretaining strong accountability. In our scheme an honest user may enjoy fullanonymity, but dishonest users who do not pay their bill have their identityrevealed. In contrast to existing revocable anonymity systems, our proposedscheme requires less trust in an external authority, while simultaneouslymaking accountability easier (and less costly) to achieve