TRUSTWORTHY TIMESTAMPS AND CERTIFIABLE CLOCKS USING LOGS LINKED BY CRYPTOGRAPHIC HASHES

• US 20080201580A1
• Filed: 02/21/2007
• Published: 08/21/2008
• Est. Priority Date: 02/21/2007
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Piersol, Kurt, Savitzky, Stephen
• Granted Patent: US 8,006,094 B2
• Time in Patent Office: Days
• US Class Current: 713/189
• CPC Class Codes: G06F 21/725 operating on a secure reference time value
• CPC Class Codes: H04L 9/3236 using cryptographic hash functions
• CPC Class Codes: H04L 9/3297 involving time stamps, e.g. generation of time stamps
• CPC Class Codes: H04L 9/50 using hash chains, e.g. blockchains or hash trees

Abstract

A method and apparatus for creating and/or using trustworthy timestamps and certifiable clocks using logs linked by cryptographic hashes. In one embodiment, the method comprises maintaining a first, chained-hash log; associating a first clock with the chained-hash log, and entangling the first log; with a second by adding a time-stamped synchronization entry to the chained-hash log, where the synchronization entry has a second time indication associated with the second log and a hash of one or more entries in the first log.

Claims

1. A method comprising:

maintaining a first, chained-hash log;

associating a first clock with the chained-hash log; and

entangling the first log with a second log by adding a time-stamped synchronization entry to the chained-hash log, the synchronization entry having a second time indication associated with the second log and a hash of one or more entries in the first log.

2. The method defined in claim 1 wherein the hash associated with the second log is a result of applying a hash to all entries in the first log.

3. The method defined in claim 1 wherein the hash associated with the second log is a result of applying a hash to a previous entry in the first log.

4. The method defined in claim 1 further comprising tracing log entanglements back to a trustworthy clock.

5. The method defined in claim 4 further comprising using results of tracing log entanglements back to a trustworthy clock to prove a version of a document existed at an identified time.

6. The method defined in claim 5 wherein the identified time comprises a time on or before a date.

7. The method defined in claim 4 further comprising determining a level of accuracy of the clock based on an assessment of accuracy of a clock associated with the second event log.

8. The method defined in claim 4 further comprising determining reliability of timestamps based on observed clock accuracy and the reputation of at least a device that maintains the second event log.

9. The method defined in claim 4 further comprising annotating entries in the first log with corrections to previously-issued timestamps based on results of tracing log entanglements back to a trustworthy clock.

10. The method defined in claim 4 further comprising determining a bound on accuracy of a clock associated with the first log based on an assessment of accuracy of a clock associated with the second log.

11. The method defined in claim 4 further comprising determining a measure of clock drift and estimating an offset between the clock and a clock associated with the second log using synchronization points resulting from synchronizing the first and second logs.

12. The method defined in claim 1 further comprising adding a time-stamped log entry into a second log containing an indication of the clock of the first log and a hash of the first event log, such that log entries in the first and second logs are entangled.

13. The method defined in claim 12 wherein each second log comprises a hash-connected chain of entries.

14. The method defined in claim 1 wherein the first log comprises one or more entries, and further wherein at least one of the one or more entries comprises one or more event times and document hashes.

15. The method defined in claim 1 further comprising annotating one or more entries in the first log with a correction.

16. The method defined in claim 15 wherein the correction is based on an identified difference between the clock and an indication of time of a second clock.

17. The method defined in claim 16 wherein the indication of time of the second clock is from a trustworthy source.

18. The method defined in claim 1 wherein hashes in the first logic are cryptographic hashes.

19. A method comprising

synchronizing a first hash-chained log with a second hash-chained log by adding a time-stamped log entry into the first log containing a first time indication of a clock associated with the second log;

and

producing one or more document timestamps traceable to a trusted source using the first and second logs cross-connected through synchronization entries added as part of a synchronization process.

20. The method defined in claim 19 wherein the time-stamped log entry includes a hash of the second log.

21. The method defined in claim 19 wherein the document timestamps have provable error bounds using the first and second logs.

22. A method comprising:

exchanging log information to synchronize a pair of hash-chained logs that each have clocks; and

placing a bound on accuracy of a clock associated with one log in the pair of logs based on an assessment of accuracy of a clock associated with the other log in the pair of logs.

23. A method comprising:

updating a clock used for time-stamping entries in a hash-chained log; and

correcting one or more log entries of a log based on the updated clock.

24. The method defined in claim 23 wherein correcting one or more log entries of a log based on the updated clock comprises annotating the one or more log entries with corrections.

25. The method defined in claim 23 further comprising connecting to a second device considered trustworthy, and wherein updating a clock used by the first device when time-stamping entries in the log is performed using a clock associated with the second device.

26. The method defined in claim 25 wherein the trustworthy device is a server.