Patent ID: 7386126

Claim:
A content protection system including a key data generation apparatus that uses a tree structure to manage a device key held by a terminal apparatus, and the terminal apparatus, the key data generation apparatus comprising: a conversion unit operable to convert first key data for use in the content, by performing a predetermined conversion with use of conversion information generated for the device key, thereby generating second key data; an encryption unit operable to encrypt the second key data using the device key, thereby generating encrypted key data; a header information generation unit for generating header information that is for generating the conversion information, and that is generated based on positional information, in a tree structure, of the device key used to generate the encrypted key data; and an output unit operable to output the encrypted key data having the header information appended thereto, and a terminal apparatus that includes: a holding unit operable to hold a plurality of device keys; a holding unit operable to hold positional information of the terminal apparatus in the tree structure; an obtaining unit operable to obtain the encrypted key data and the header information that is appended to the encrypted key data; a decryption unit operable to decrypt the encrypted key data using a device key held by the terminal apparatus, thereby generating second key data; a conversion unit operable to generate conversion information from the header information and the positional information, and convert the second key data, by performing a predetermined conversion with the use of the generated conversion information, thereby generating first key data; and a content usage unit operable to use the content, based on the first key data.