Patent ID: 7072865

Claim:
A broadcast receiving method comprising: storing first control information in a storage device of a receiver, the first control information containing identification information unique to the receiver and contract information for selecting some of a plurality of different channels, the first control information required for the receiver to select broadcasted and encrypted contents information, the contract information including a work key encrypted by a master key; receiving second control information with the receiver via a bi-directional communications channel, the second control information containing contract information for updating; periodically updating at a first period the contract information of the first control information in the storage device to the contract information contained in the second control information; sending back a receipt acknowledgement from the receiver via the bi-directional communications channel when the contract information of the first control information is updated; periodically receiving encrypted key information which is independent of the receiver and broadcasted to decrypt the contents information at a second period shorter than the first period, the encrypted key information being encrypted by the work key; decrypting the encrypted key information to obtain decrypted key information; storing the decrypted key information in the storage device; determining whether the stored decrypted key information is valid based on the contract information; and decrypting the contents information based on the decrypted key information that has been determined to be valid.