Content data, transmitting apparatus, receiving apparatus and decoding method

A transmitting apparatus comprising:

• an initialization vector generating unit for generating an initialization vector for encrypting stream data with a stream encryption method;
• an encryption unit for initializing a stream encryption module using the initialization vector generated by the initialization vector generating unit, and performing stream encryption on the stream data using the stream encryption module initialized;
• an encryption packet generating unit for generating an encryption packet containing stream-encrypted data encrypted by the encryption unit;
• an initialization packet generating unit for generating an initialization packet containing the initialization vector and time information indicating when a next initialization vector of the initialization vector will be sent;
• and
• a transmission unit for transmitting the initialization packet and the encryption packet by broadcast/multicast.

A receiving apparatus comprising:

• a reception unit for receiving an initialization packet containing an initialization vector for encrypting stream data and time information indicating when a next initialization vector of the initialization vector will be sent, and an encryption packet containing stream-encrypted data encrypted using the initialization vector;
• a decryption unit for initializing a stream encryption module using the initialization vector contained in the initialization packet, and decrypting stream-encrypted data contained in the encryption packet;
• a detection unit for detecting a reception error of a packet received by the reception unit;
• and
• a control unit for controlling the decryption unit so as to continuously decrypt the stream-encrypted data when a timing at which the detection unit detects a reception error of a packet is before a predetermined range defined based on a time at which the next initialization vector will be sent, and so as to stop decrypting the stream-encrypted data until a new initialization packet is received when the timing is within the predetermined range.

A receiving apparatus comprising:

• a reception unit for receiving an initialization packet containing an initialization vector for encrypting stream data, a next initialization vector of the initialization vector and time information indicating when the next initialization vector is scheduled to be sent, and an encryption packet containing stream-encrypted data encrypted using the initialization vector,
• a decryption unit for initializing a stream encryption module using the initialization vector contained in the initialization packet, and decrypting stream-encrypted data contained in the encryption packet;
• a detection unit for detecting a reception error of a packet received by the reception unit;
• and
• a control unit for controlling the decryption unit so as to continuously decrypt the stream-encrypted data when a timing at which the detection unit detects a reception error of a packet is before a predetermined range defined based on a time at which the next initialization vector will be sent, and so as to initialize the stream encryption module using the next initialization vector and decrypt stream-encrypted data contained in an encryption packet received after the timing at which the reception error is detected using the initialized stream encryption module when the timing is within the determined range.

A decoding method comprising:

• receiving step for receiving an initialization packet containing an initialization vector for encrypting stream data and time information indicating when a next initialization vector of the initialization vector will be sent, and an encryption packet containing stream-encrypted data encrypted using the initialization vector with a receiver;
• decrypting step for initializing a stream encryption module using the initialization vector contained in the initialization packet and decrypting stream-encrypted data contained in the encryption packet with the stream encryption module;
• detecting step for detecting a reception error of a packet received in the receiving step;
• and
• controlling step for controlling the decryption step so as to continuously decrypt the stream-encrypted data when a timing at which a reception error of a packet is detected in the detecting step is before a predetermined range defined based on a time at which the next initialization vector will be sent, and so as to stop decrypting the stream-encrypted data until a new initialization packet is received when the timing is within the predetermined range.