Patent ID: 8046302

Claim:
A Digital Rights Management (DRM) system for content copyright protection, the DRM system comprising: a time security module which determines time change information when a user arbitrarily changes a standard time related to a selected content to a changed time as a value of a difference between a value of the standard time, prior to being changed by the user, and a value of the changed time; and a time security list management module which manages content, right to use information related to the content and the time change information based on a tree structure comprising: a top node which stores the time change information, and nodes subordinate to the top node, wherein the subordinate nodes store the right to use information with an effective time information which is set when the subordinate node for a respective right to use information is created, wherein the time security module calculates a current time based at least on a sum of the value of the time change information stored in the top node and the value of the changed time, the right to use information of the selected content stored in a corresponding subordinate node is checked by the DRM system to determine whether the right to use information is effective based on comparing the current time with the effective time, and when new content and corresponding right information are added, the time security list management module generates a new top node higher than a current top node which becomes the top node in the tree structure, and at least one of the time security module and the time security list management module is embodied on a computer.