Time data checking unit, electronic device and method for checking a time indication

1. A time data checking device, comprising:

a time data provision unit that provides a first time indication which can be changed by a user;

a first memory that stores the first time indication;

a time indication change determining unit that determines a change in the first time indication performed externally to the time data checking device, such that a changed first time indication is generated by changing the first time indication to become the changed first time indication;

a time indication difference determining unit that determines the difference between the stored first time indication and the changed first time indication;

a second memory that stores the difference between the stored first time indication and the changed first time indication or the changed first time indication or both;

a third memory that stores a trustworthy second time indication; and

a checking unit that checks whether a predetermined criterion is met by using the first time indication, the difference between the stored first time indication and the changed first time indication, and the trustworthy second time indication,

wherein the stored first time indication cannot be changed by a user, or wherein the stored difference between the stored first time indication and the changed first time indication or the changed first time indication or both cannot be changed by a user.

2. The time data checking device as claimed in 1 , wherein the time data provision unit is a real-time clock circuit which provides the first time indication as real-time clock time indication.

3. The time data checking device as claimed in 1 , wherein at least one of the first memory, the second memory, and the third memory is set up as nonvolatile memory.

4. The time data checking device as claimed in 1 , wherein the trustworthy second time indication is a digital rights management time indication which specifies how long media data are allowed to be used or up to which time media data are allowed to be used or both.

5. The time data checking device as claimed in 4 , wherein the checking unit checks whether media data to which the second time indication is allocated are allowed to be displayed.

6. The time data checking device as claimed in 5 , wherein the media data is encrypted, and

the time data checking device further comprises a decryption unit that decrypts the media data using the at least one cryptographic key.

7. The time data checking device as claimed in 1 , further comprising a key memory that stores at least one cryptographic key to which the second time indication is allocated, and the validity of the at least one cryptographic key can be determined using the second time indication.

8. An electronic device with a time data checking device, comprising:

a time data provision unit that provides a first time indication which can be changed by a user;

a first memory that stores the first time indication;

a time indication change determining unit that determines a change in the first time indication performed externally to the time data checking device, such that a changed first time indication is generated by changing the first time indication to become the changed first time indication;

a time indication difference determining unit that determines the difference between the stored first time indication and the changed first time indication;

a second memory that stores the difference between the stored first time indication and the changed first time indication or the changed first time indication or both;

a third memory that stores a trustworthy second time indication; and

a checking unit that checks whether a predetermined criterion is met by using the first time indication, the difference between the stored first time indication and the changed first time indication, and the trustworthy second time indication,

wherein the stored first time indication cannot be changed by a user, or the stored difference between the stored first time indication and the changed first time indication or the changed first time indication or both cannot be changed by a user.

9. The electronic device as claimed in 8 , further comprising a media data display device which displays media data, the media data display device being coupled to the time data checking device and only displaying the media data when the checking unit has determined that the criterion is met.

10. The electronic device as claimed in 8 , further comprising at least one of a screen for displaying graphic media data and a loudspeaker for representing audio media data.

11. The electronic device as claimed in 8 , set up as communication device.

12. A method for checking a time indication, performed by a time data checking device, comprising:

providing a first time indication, which can be changed by a user, by a time data provision unit;

storing the first time indication in a first memory;

determining a change in the first time indication, performed externally to the time data checking device, such that a changed first time indication is generated by changing the first time indication to become the changed first time indication;

determining the difference between the stored first time indication and the changed first time indication;

storing the difference between the stored first time indication and the changed first time indication or the changed first time indication or both in a second memory;

storing a trustworthy second time indication in a third memory; and

checking whether a predetermined criterion is met by using the first time indication, the difference between the stored first time indication and the changed first time indication and the trustworthy second time indication,

wherein the stored first time indication cannot be changed by a user, or the stored difference between the stored first time indication and the changed first time indication or the changed first time indication or both cannot be changed by a user.

13. A time data checking device, comprising:

a real-time clock that provides a real-time clock time indication which can be changed by a user;

a first memory that stores the real-time clock time indication;

a time indication change determining unit that determines a change in the real-time clock time indication, performed externally to the time data checking device, such that a changed real-time clock time indication is generated by changing the real-time clock time indication to become the changed real-time clock time indication;

a time indication difference determining unit that determines the difference between the stored real-time clock time indication and the changed real-time clock time indication;

a second memory that stores the difference between the stored real-time clock time indication and the changed real-time clock time indication or the changed real-time clock time indication or both;

a third memory that stores a trustworthy digital rights management (DRM) time indication; and

a checking unit that checks whether a predetermined criterion is met by using the real-time clock time indication, the difference between the stored real-time clock time indication and a changed real-time clock time indication and the trustworthy DRM time indication,

wherein the stored real-time clock time indication cannot be changed by a user, or the stored difference between the stored real-time clock time indication and the changed real-time clock time indication or the changed real-time clock time indication or both cannot be changed by a user.

14. A system comprising:

time data checking device, comprising:

a real-time clock that provides a real-time clock time indication which can be changed by a user;

a first memory that stores the real-time clock time indication;

a time indication change determining unit that determines a change in the real-time clock time indication, performed externally to the time data checking device, by means of which a changed real-time clock time indication is generated by changing the real-time clock time indication to become the changed real-time clock time indication;

a time indication difference determining unit that determines the difference between the stored real-time clock time indication and the changed real-time clock time indication;

a second memory that stores the difference between the stored real-time clock time indication and the changed real-time clock time indication or the changed real-time clock time indication or both;

a third memory that stores a trustworthy digital rights management (DRM) time indication; and

a checking unit that checks whether a predetermined criterion is met by using the real-time clock time indication, the difference between the stored real-time clock time indication and the changed real-time clock time indication and the trustworthy DRM time indication,

wherein the stored real-time clock time indication cannot be changed by a user, or the stored difference between the stored real-time clock time indication and the changed real-time clock time indication or the changed real-time clock time indication or both cannot be changed by a user; and

a digital rights management server unit that provides the trustworthy DRM time indication to the time data checking device.

15. A time data checking device, comprising:

a time data provision means for providing a first time indication which can be changed by a user;

a first memory that stores the first time indication;

a time indication change determining means for determining a change in the first time indication performed externally to the time data checking device, by means of which a changed first time indication is generated by changing the first time indication to become the changed first time indication;

a time indication difference determining means for determining the difference between the stored first time indication and the changed first time indication;

a second memory that stores the difference between the stored first time indication and the changed first time indication or the changed first time indication or both;

a third memory that stores a trustworthy second time indication; and

a checking means for checking whether a predetermined criterion is met by using the first time indication, the difference between the stored first time indication and the changed first time indication, and the trustworthy second time indication,

wherein the stored first time indication cannot be changed by a user, or wherein the stored difference between the stored first time indication and the changed first time indication or the changed first time indication or both cannot be changed by a user.