Patent ID: 7380134

Claim:
An information recording/reproducing apparatus comprising: a setting section which receives content information and sets a reproduction enable condition for the received content information; a power supply interruption detector which detects that a power supply has been interrupted; an updating section which updates the reproduction enable condition, including an area already reproduced and an area not reproduced yet, when reproduction of the content information is started and stopped, or when the power supply interruption detector detects interruption of the power supply and playback is stopped; an encryption section which encrypts the content information with key information and stores the encrypted content information; an arithmetic section which executes an arithmetic processing for information about the reproduction enable condition updated by the updating section and stores an arithmetic result; a reproduction enable condition determining section which determines, upon receipt of a reproduction start instruction, whether the instruction coincides with the reproduction enable condition updated by the updating section; an alternation determining section which obtains an arithmetic result by executing an arithmetic processing for information about the reproduction enable condition used by the reproduction enable condition determining section when the reproduction enable condition determining section determines that the reproduction start instruction coincides with the reproduction enable condition, compares the obtained arithmetic result with the arithmetic result stored by the arithmetic section, and determines that the reproduction enable condition has not been altered when the compared arithmetic results coincide; a decryption section which decrypts the content information encrypted by the encryption section using an encryption key and outputs the decrypted content information when the alternation determining section determines that alternation has not occurred, and does not decrypt the content information or does not output a signal decrypted from the content information using the encryption key when the alternation determining section determines that alternation has occurred.