Abstract: An HDCP encrypting section of an encrypting apparatus encrypts a content signal using a device key and transmits the encrypted signal. An HDCP decrypting section of a decrypting apparatus receives the encrypted content signal and decrypts the signal using the device key. Device key encryption processing software encrypts the device key using a predetermined private key and writes the encrypted device key in a memory of the encrypting apparatus. A device key protecting circuit reads the encrypted device key from the memory, decrypts the encrypted device key and supplies the decrypted device key to the HDCP encrypting section. In the event of an unauthorized access to the device key protecting circuit, a system reconstructing circuit reconstructs a scheme for decrypting the device key in the device key protecting circuit.