METHOD AND APPARATUS FOR ADJUSTING DECRYPTION KEYS

• US 20100104100A1
• Filed: 05/08/2007
• Published: 04/29/2010
• Est. Priority Date: 05/08/2007
• Status: Abandoned Application

• Current Assignee: Thomson Licensing (Vantiva SA)
• Original Assignee: Thomson Licensing (Vantiva SA)
• Inventors: William Gibbens, Redmann
• Application Number:
  US12/450,533
• Publication Number:
  US 20100104100A1
• Time in Patent Office: Days
• US Class Current: 380/277
• CPC Class Codes: H04L 2209/60 Digital content management, e.g. content distribution
• CPC Class Codes: H04L 63/0428 wherein the data content is protected, e.g. by encrypting or encapsulating the payload
• CPC Class Codes: H04L 9/0891 Revocation or update of secret information, e.g. encryption key update or rekeying
• CPC Class Codes: H04L 9/12 Transmitting and receiving encryption devices synchronised or initially set up in a particular manner
• CPC Class Codes: H04L 9/3297 involving time stamps, e.g. generation of time stamps

Abstract

In a digital cinema system, a Secure Clock can drift over time, possibly presenting the ability to playout a digital cinema presentation near the end of the validity interval of a decryption key. To accommodate for the drift in the Secure Clock, the validity interval of the decryption key is adjusted in accordance with the time difference between a secure time value and a present time value.

Claims

1. A method comprising the step of:

adjusting a validity interval of a key for decrypting content in accordance with a time difference between a secure time value and a current time value.

2. The method according to claim 1 wherein the adjusting step further comprises the steps of:

reading a secure clock to obtain the secure time value; and

comparing the secure to the current time value.

3. The method according to claim 1 wherein the adjusting step further comprises the steps of:

determining a time zone offset for a desired exhibition location; and

converting the validity interval from Greenwich Mean Time to local time in accordance with the time zone offset.

4. The method of claim 1 wherein adjustment of the validity interval of the key commences upon acceptance of an order to generate a key for content decryption.

5. The method according to claim 1 further comprising the step of distributing the key following validity adjustment to media block that decrypts the content in accordance with the key.

6. A method comprising the step of:

adjusting a validity interval of a content decryption key in accordance with a time difference between a secure time value and a current time value; and

decrypting an encrypted digital cinema presentation in accordance with the content decryption key.

7. The method according to claim 6 wherein the adjusting step further comprises the steps of:

reading a secure clock to obtain the secure time value; and

comparing the secure to the current time value.

8. The method according to claim 6 wherein the adjusting step further comprises the steps of:

determining a time zone offset for a desired exhibition location; and

converting the validity interval from Greenwich Mean Time to local time in accordance with the time zone offset.

9. The method of claim 6 wherein adjustment of the validity interval of the key commences upon acceptance of an order to generate a key for content decryption.

10. The method according to claim 9 further comprising the step of distributing the key following validity adjustment to a screen server.

11. Digital cinema apparatus comprising:

a secure clock for providing a secure time value for determining the time validity of a decryption key;

a reference clock for providing a current time value; and

a secure clock monitor for establishing a time difference value between a secure time value and a current time value for adjusting a validity interval associated with the decryption key.

12. The apparatus according to claim 11 further comprising a database for storing the time difference value.

13. The apparatus according to claim 11 further comprising a key generator for adjusting the decryption key in accordance with the time difference value stored in the database.