Patent ID: 8165304

Claim:
A domain digital rights management (DRM) system comprising: at least one user device including a hardware processor and at least one domain manager device including another hardware processor belonging to a domain; and a license server for creating domain encryption keys corresponding to the at least one domain manager device and the at least one user device, respectively, and providing the at least one domain manager device and the at least one user device with the respective domain encryption keys; wherein when the at least one user device requests to reproduce contents encrypted by a contents encryption key: a) the license server encrypts the contents encryption key with one of the respective domain encryption keys and then encrypts the encrypted contents encryption key with another of the respective domain encryption keys to produce a double encrypted contents encryption key according to a commutative encryption scheme, and b) the license server transmits the double encrypted contents encryption key to both the user device and the at least one domain manager device which enables the at least one domain manager device and the at least one user device to decrypt the double encrypted contents encryption key by using both of the respective domain encryption keys, and decrypt the encrypted contents using the contents encryption key.