Information recording/reproducing apparatus and method of executing encryption processing

1. 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.

2. An information recording/reproducing apparatus according to claim 1 , wherein the arithmetic section and the alternation determining section executes an arithmetic processing for relationship information which indicates a relationship between the reproduction enable condition set by the setting section and the content information, and information about the reproduction enable condition, and compares arithmetic results.

3. An information recording/reproducing apparatus according to claim 1 , wherein the encryption key used by the encryption section and the decryption section is relationship information which indicates a relationship between the content information and the reproduction enable condition, the apparatus encrypts the relationship information with a second encryption key, stores the encrypted relationship information, decrypts the encrypted relationship information using the second encryption key when the alternation determining section determines that alternation has not occurred, and reproduces or outputs the decrypted relationship information.

4. An information recording/reproducing apparatus according to claim 1 , wherein the reproducing enable condition contains reproduction count information which indicates a number of times of reproduction of a predetermined area of the content information.

5. An information recording/reproducing apparatus according to claim 1 , wherein each of the arithmetic section and the alternation determining section executes an arithmetic processing for relationship information which indicates a relationship between the reproduction enable condition set by the setting section and the content information, information about the reproduction enable condition, and the encryption key used by the encryption section and the decryption section, and compares arithmetic results.

6. An information recording/reproducing apparatus according to claim 1 , wherein each of the arithmetic portion and the alternation determining section executes hash calculation for the reproduction enable condition and obtains an arithmetic result.

7. A method of processing information from an information recording/reproducing apparatus comprising:

receiving content information;

setting a reproduction enable condition for the received content information;

detecting interruption of power supply;

updating 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 interruption of the power supply has been detected and playback is stopped;

encrypting the content information with encryption key information;

storing the encrypted content information;

executing an arithmetic processing for information about the reproduction enable condition updated by the updating section and storing an arithmetic result;

determining, upon receipt of a reproduction start instruction, whether the instruction coincides with the updated reproduction enable condition;

obtaining an arithmetic result by executing an arithmetic processing for information about the reproduction enable condition when it is determined that the reproduction start instruction coincides with the reproduction enable condition;

comparing the obtained arithmetic result with the stored arithmetic result;

determining that the reproduction enable condition has not been altered when the compared arithmetic results coincide; and

decrypting the encrypted content information by using an encryption key outputting the decrypted content information when it is determined that alternation has not occurred.

8. A processing method according to claim 7 , wherein the executing an arithmetic processing and the obtaining an arithmetic result performs an arithmetic processing for relationship information that indicates a relationship between the set reproduction enable condition and the content information, and information about the reproduction enable condition, and compares arithmetic results.

9. A processing method according to claim 7 , wherein the encryption key and the decrypting includes relationship information that indicates a relationship between the content information and the reproduction enable condition, encrypts the relationship information with a second encryption key, storing the encrypted relationship information, decrypting the encrypted relationship information using the second encryption key when it is determined that alternation has not occurred, and reproducing or outputting the decrypted relationship information.

10. A processing method according to claim 7 , wherein the reproducing enable condition contains reproduction count information which indicates a number of times of reproduction of a predetermined area of the content information.

11. A processing method according to claim 7 , wherein each of the executing an arithmetic processing and the obtaining an arithmetic result performs an arithmetic processing for relationship information which indicates a relationship between the reproduction enable condition set by the setting section and the content information, information about the reproduction enable condition, and the encryption key and the decrypting, and comparing arithmetic results.

12. A processing method according to claim 7 , each of the executing an arithmetic processing and the obtaining an arithmetic result performs hash calculation for the reproduction enable condition and obtains an arithmetic result.