Secure clock with grace periods

• US 8,438,645 B2
• Filed: 04/27/2005
• Issued: 05/07/2013
• Est. Priority Date: 04/27/2005
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Jain, Amit, Evans, Brian P., Strom, Clifford P., Cutter, Benjamin B. Jr.
• Primary Examiner(s): POWERS, WILLIAM S
• Application Number:
  US11/116,884
• Publication Number:
  US 20060248596A1
• Time in Patent Office: 2,932 Days
• Field of Search: 713/168, 713/156, 705/37, 705/59, 709/243, 709/231, 726/26, 726/27
• US Class Current: 726/26
• CPC Class Codes: G06F 21/1073 Conversion
• CPC Class Codes: G06F 21/725 operating on a secure reference time value
• CPC Class Codes: G06F 2221/2137 Time limited access, e.g. to a computer or data

Abstract

A system of controlling playback of digital media. A system of controlling playback of digital media comprising a CE device having a secure clock and a license having a specified grace period disposed upon the CE device in which a digital media file governed by the license may be played for the grace period upon failure of the secure clock.

Claims

1. A system for allowing playback of a digital media file, the system comprising:

a consumer electronics (CE) device comprising a secure clock that cannot be adjusted by a user of the CE device, the secure clock configured for synchronizing to a trusted time provided by a trusted time authority server, the CE device configured for entering, in response to the secure clock not being synchronized to the trusted time but previously being synchronized to the trusted time, a grace period mode, the CE device further configured for maintaining, until the secure clock is re-synchronized to the trusted time, the grace period mode, the CE device further configured for not allowing playback of the digital media file and for not entering the grace period mode in response to the CE device being in an unset mode, wherein the unset mode indicates that the secure clock has never been synchronized to the trusted time provided by the trusted time authority server;

a license comprising a grace period, the license disposed upon the CE device and associated with the digital media file;

the CE device further configured for allowing, in response to the entering and the maintaining the grace period mode, the playback of the digital media file until the secure clock is re-synchronized to the trusted time or until the grace period expires.

2. The system for allowing the playback of the digital media file of claim 1, the CE device further configured for periodically synchronizing the secure clock with the trusted time authority.

3. The system for allowing the playback of the digital media file of claim 1, further comprising:

the CE device further configured to determine that the secure clock has failed; and

the CE device further configured to play, in response to the determining and according to the grace period, the digital media file governed by the license.

4. The system for allowing the playback of the digital media file of claim 3, the CE device further configured to periodically record a last known good time in a secure store.

5. The system for allowing the playback of the digital media file of claim 4, the CE device further configured to set the secure clock to the last known good time in response to a failure of the secure clock.

6. The system for allowing the playback of the digital media file of claim 5, wherein the grace period is reduced as time progresses from the last known good time.

7. The system for allowing the playback of the digital media file of claim 1, the entering in further response to a failure of the secure clock.

8. The system for allowing the playback of the digital media file of claim 1, wherein the license is a time based license.

9. A method of allowing playback of a digital media file on a consumer electronics (CE) device, the method comprising:

determining a failure to synchronize a clock of the CE device to a trusted time provided by a trusted time authority, wherein the clock cannot be adjusted by a user of the CE device;

setting, by the CE device in response to the clock previously being synchronized to the trusted time, the clock to a last known good time;

entering, by the CE device in response to the clock previously being synchronized to the trusted time, a grace period mode;

maintaining, by the CE device until the clock is re-synchronized to the trusted time, the grace period mode; and

allowing, by the CE device in response to the entering and the maintaining the grace period mode, the playback of the digital media file, wherein the CE device is configured for not allowing playback of the digital media file and for not entering the grace period mode in response to the CE device being in an unset mode, wherein the unset mode indicates that the clock has never been synchronized to the trusted time provided by the trusted time authority.

10. The method of claim 9 further comprising saving a grace period start time.

11. The method of claim 9 wherein the allowing continues while maintaining the grace period mode until the grace period expires.

12. A method of providing a grace period comprising:

obtaining a clock state of a secure clock of a consumer electronics (CE) device, wherein the secure clock cannot be adjusted by a user of the CE device, and wherein the secure clock is configured for synchronizing to a trusted time provided by a trusted time authority server;

setting, by the CE device in response to the secure clock not being synchronized to the trusted time but previously being synchronized to the trusted time, the secure clock to a last known good time;

setting, by the CE device in response to the secure clock not being synchronized to the trusted time but previously being synchronized to the trusted time, the clock state to a grace period mode; and

saving the last known good time as a grace period start time, wherein the CE device is configured for not entering the grace period mode in response to the CE device being in an unset mode, wherein the unset mode indicates that the secure clock has never been synchronized to the trusted time provided by the trusted time authority server.

13. The method of providing a grace period of claim 12, wherein the grace period start time indicates a start of the grace period.

14. The method of providing a grace period of claim 13, wherein a duration of the grace period is specified in a license corresponding to a media file.

15. The method of providing a grace period of claim 14, further comprising playing the media file no longer than the grace period duration.