Systems, methods, software, and components using tamper-proof real-time clock
View Patent ↗The write-access control line for an RTC is combined with a clear line for an RTC signature register, so that changes to the RTC will cause subsequent reads to return an invalidity flag.
1. A device, comprising:
instruction execution logic operable to execute a plurality of software instructions;
a real-time clock configured to maintain and provide a system time;
a signature storage register having a write-access control line inaccessible to a user, wherein the signature storage register is configured to hold a digital signature for the real-time clock generated by digital rights management software when a software license is granted, wherein the signature storage register includes an invalidation control line connected to the real-time clock;
wherein the invalidation control line forces the signature register into an invalid state whenever the write-access control line goes active.
2. The device of claim 1 , wherein the real-time clock is configured to maintain the system time in nonvolatile memory.
3. The device of claim 1 , wherein the digital signature is cleared when the system time is modified.
4. The device of claim 1 , wherein the signature storage register is write only.
5. The device of claim 1 , wherein digital rights management (DRM) software verifies the digital signature by generating a new signature for the real-time clock and determining if the new signature corresponds to the digital signature maintained in the signature storage register.
6. The device of claim 1 , wherein the digital signature is generated based on a unique hardware-encoded value.
7. The device of claim 1 , wherein the digital signature is generated based on a unique hardware-encoded value and a current system time.
8. The device of claim 1 , wherein the invalidation control line is a clear input.
9. The device of claim 1 , wherein the invalidation control line is electrically connected to the write-access control line.
10. A method, comprising:
receiving a software license grant;
generating a digital signature for a real-time clock configured to maintain and provide a system time;
storing the digital signature in a signature storage register having a write-access control line inaccessible to a user, wherein the signature storage register is configured to hold a digital signature for the real-time clock, wherein the signature storage register includes an invalidation control line connected to the real-time clock;
wherein the invalidation control line forces the signature register into an invalid state whenever the write-access control line goes active.
11. The method of claim 10 , wherein the real-time clock is configured to maintain the system time in nonvolatile memory.
12. The method of claim 10 , wherein the digital signature is cleared when the system time is modified.
13. The method of claim 10 , wherein the signature storage register is write only.
14. The method of claim 10 , wherein digital rights management (DRM) software verifies the digital signature by generating a new signature for the real-time clock and determining if the new signature corresponds to the digital signature maintained in the signature storage register.
15. The method of claim 10 , wherein the digital signature is generated based on a unique hardware-encoded value.
16. The method of claim 10 , wherein the digital signature is generated based on a unique hardware-encoded value and a current system time.
17. The method of claim 10 , wherein the invalidation control line is a clear input.
18. The method of claim 10 , wherein the invalidation control line is electrically connected to the write-access control line.