ConCert: Content Revocation Using Certificates

Abstract

Content reuse on the Web is becoming even more common since the Web 2.0 “phenomenon”. However, each time content is reused certain information is either completely lost (for example through excerpts) or gets harder to verify. This reduces the content’s quality and thus the content’s value for viewers. Among the lost infor- mation are origin, author, creation time, or if the author still endorses the content. We propose preserving this information in a cryptographically protected content certificate (ConCert). This X.509 compatible certificate binds the content to the author’s public-key. Using a hash tree we allow viewers to verify the properties, even if parts from the original content have been omitted before re-publication. The author can indicate which parts can be omitted during certificate generation in a policy. Furthermore, the author can indicate a change in his consent to the content itself or to its re-publication by revoking the content’s certificate.