Redistributing time-based rights between consumer devices for content sharing in DRM system

Device-based digital rights management (DRM) systems tightly bind rights for content to a device. However, it can decrease the consumers' convenience because it disturbs consumers who want to use the already purchased content with their other devices freely. Previous research into solving this problem still have burdens such as restricting the number of devices that a consumer can use and requiring a special device that manages content sharing. In this paper, we propose a new rights sharing scheme which does not restrict the number of devices that a consumer can use and does not require a specialized device. In our scheme, the right to use content is represented as the right to use the content for a certain amount of time. Consumers can use the content with any of their devices by redistributing the usage amount of time between devices. The redistribution process only requires local synchronization among participating devices. To prevent illegal content sharing and to detect illegally increased content usage time, the amount of time that a consumer can have is limited and the rights for each unit of time has a unique number to prevent illegal duplications. We present data structures and protocols, analyze security properties of our scheme, compare our scheme with related work, and evaluate our scheme through implementation.