Patent ID: 7567674

Claim:
A content transmission apparatus that encrypts and transmits contents of digital broadcasting, comprising: a storage unit provided with a memory to store a scrambling key that changes as time passes, a content key provided to each content, a network key retained for a time period longer than a duration of the contents, and a master key provided commonly to a receiver side; a content encryption unit configured to encrypt the contents using the scrambling key into encrypted contents; a related information encryption unit configured to encrypt first information related to the contents, the first information including at least the scrambling key using the content key into encrypted related information; a content key related information encryption unit configured to encrypt second information related to the content key, the second information including at least the content key using a work key into encrypted content key related information; a work key related information encryption unit configured to encrypt third information related to the work key, the third information including at least the work key using the encrypted work key related information into encrypted work key related information; a multiplexer unit configured to multiplex the encrypted work key related information, the encrypted content key related information, and the encrypted contents; and a multiplexed encrypted content transmission unit configured to transmit the multiplexed encrypted contents multiplexed by the multiplexer unit, wherein if a plurality of security modules are correspondingly provided in reception apparatuses at the receiver side, each security module storing decrypted content key related information and being unreadable from exterior, the plurality of security modules being grouped into a plurality of groups, different work keys are used for different groups of the plurality of security modules, each security module has a plurality of intrinsic keys for encrypting information outputted form the security module, and the content transmission apparatus further comprises an intrinsic key related information encryption unit configured to encrypt the plurality of intrinsic keys into encrypted intrinsic key related information using the master key.