Patent ID: 8468350

Claim:
A content transmission apparatus comprising: an authenticator configured (i) to perform an authentication for a content reception apparatus, (ii) to share an authentication key with said content reception apparatus, (iii) to send a request for transmission range acknowledgement and authentication information to said content reception apparatus, (iv) to receive a response transmitted from said content reception apparatus responding to said request for transmission range acknowledgement, and (v) to share an exchange key with said content reception apparatus; an encryptor configured to encrypt a content to be transmitted to said content reception apparatus based on said exchange key; and a timer used for measuring a time interval between transmission of said request for transmission range acknowledgement to said content reception apparatus and reception of said response transmitted from said content reception apparatus responding to the transmission of said request for transmission range acknowledgement; wherein, said authenticator measures said time interval between said transmission of said request and said reception of said response using said timer, and when a measurement value of said time interval exceeds a predetermined value, said authenticator does not share said exchange key with said content reception apparatus; and wherein, said response of said request for transmission range acknowledgement from said content reception apparatus includes a data generated based on said authentication information and said authentication key, and when said data is incorrect, said authenticator does not share said exchange key with said content reception apparatus.