Patent ID: 7721088

Claim:
A terminal device in a content distribution system including a server device and said terminal device, said terminal device comprising: a processor; a receiving unit configured to receive, from said sewer device, (I) an encrypted content, and (II) content-related information including (II-i) pieces of transmission date and time information of the encrypted content and (II-ii) a plurality of content decryption keys for decrypting the encrypted content; a content-related information checking unit configured to check the content-related information using the processor; and a content use control unit configured to control use of the encrypted content, wherein the content-related information received by said receiving unit has been encrypted in Cipher Block Chaining (CBC) mode, the content-related information being a sequence of a plurality of encryption blocks, at least two of the plurality of encryption blocks in the sequence of the plurality of encryption blocks include corresponding ones of the plurality of content decryption keys, and each of the at least two encryption blocks is immediately preceded by one of the encryption blocks in which a corresponding one of the pieces of transmission date and time information is placed, said content-related information checking unit is configured to check whether or not all the pieces of transmission date and time information arranged in the plurality of respective encryption blocks and decrypted are identical, and judge that the decrypted content-related information is incorrect when all the pieces of transmission date and time information are not identical, and said content use control unit is configured to limit the use of the encrypted content when said content-related information checking unit judges that the decrypted content-related information is incorrect.