| 摘要 |
PROBLEM TO BE SOLVED: To protect a copyright from piracy in preventing illegal copies by ciphering a data with a 1st key and ciphering this 1st key with predetermined plural 2nd keys. SOLUTION: A 2nd session key Sk' is generated by a session key generating circuit 111, and is decoded by a decoding circuit 112 with a master key Mk and then ciphered by a ciphering circuit 104 with the key Mk, so that the key Sk' generated by the circuit 111 is obtained. Then, a 1st session key ciphered by the key Mk recorded on a DVD 101 is ciphered by the key Sk' and is sent to the circuit 112, where this key is decoded by the key Mk to obtain the 1st session key Mk. Then, a data ciphered by a key Sk recorded on the DVD 101 is read out, and is processed by a demodulation/ error correction circuit 118, and afterward, the received data is decoded by the circuit 112 with the key Sk to obtain a plain styled data. Thus, the decoded data does not flow in a CPU.BUS 110, and for example, even when this data is stored in a storage medium, the data cannot be reproduced to be used. Consequently, an illegal act of making unauthorized copies is prevented to protect the copyright from piracy. |
