Abstract

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 protect themselves against misbehaving users. For instance, users that do not pay their bill must be held accountable for their behavior. This tension between privacy and accountability is fundamental, however a tradeoff is not always required. In this article we propose the concept of a time capsule, that is, a verifiable encryption with timed and revocable decryptability. The time capsule together with its related protocols offer support of privacy while retaining strong accountability. In our scheme an honest user may enjoy full anonymity, but dishonest users who do not pay their bill have their identity revealed. In contrast to existing revocable anonymity systems, our proposed scheme requires less trust in an external authority, while simultaneously making accountability easier (and less costly) to achieve