Content is encrypted according to a content key (CK) ((CK(content))), (CK) is protected according to a license server public key (PU-DRM), and rights data associated with the content is protected according to (PU-DRM). The protected items are submitted as a rights label to the license server for signing....http://www.google.com/patents/US7353402?utm_source=gb-gplus-sharePatent US7353402 - Obtaining a signed rights label (SRL) for digital content and obtaining a digital license corresponding to the content based on the SRL in a digital rights management system
