How to Manage Persistent State in DRM Systems

Digital Rights Managements (DRM) systems often must manage persistent state, which includes protected content, an audit trail, content usage counts, certificates and decryption keys. Ideally, persistent state that has monetary value should be stored in a physically secure server. However, frequently the persistent state may need to be stored in a hostile environment. For example, for good performance and to support disconnected operation, recent audit records may be stored on a consumer device. The device’s user may have an incentive to alter the audit trail and thus obtain content for free. In this paper we explain the need for persistent state in DRM systems, describe several methods for maintaining persistent state depending on the system requirements, and then focus on the the special case of protecting persistent state in hostile environments.