US Patent 7536355 Content security system for screening applications

A method for securing a content is disclosed. The method generally includes the steps of (A) generating a media key by decrypting a media key block based on a device key unique to a particular player of a plurality of players, (B) modifying the media key by decryption based on a class key such that the media key is unique for each of a plurality of subscriber classes, (C) writing an encrypted title key in a media by encrypting a title key based on both the media key after modification and a media identification value unique to the media and (D) writing an encrypted content in the media by encrypting the content based on the title key.