A content protection system prevents illegal key acquisition, without checking uniqueness of device keys. The content protection system includes a key data generation apparatus and a user terminal. The key data generation apparatus converts first key data, which is for using content, based on a predetermined...http://www.google.co.uk/patents/US8144869?utm_source=gb-gplus-sharePatent US8144869 - Content protection system, key data generation apparatus, and terminal apparatus
