Method and system for preventing simultaneous use of contents in different formats derived from the same content at a plurality of places

摘要

The original content and the converted content obtained by converting the original content are encrypted by the same content key. A license containing data of use conditions such as the content key and a use period is recorded in an area of a storage medium limited for access. When the converted content is used with an external storage medium, a copy of an original license is created, a use period of the copy is changed to a use period of the converted content designated by a user, and the license is output as a converted content license to the external storage device. The use period of the original content is rewritten to prevent its overlapping with a use period defined by the converted license.