Threshold cryptography scheme for conditional access systems

• US 20040047472A1
• Filed: 05/28/2003
• Published: 03/11/2004
• Est. Priority Date: 09/24/2001
• Status: Abandoned Application

• Current Assignee: Thomson Licensing SA (Vantiva SA)
• Original Assignee: Thomson Licensing SA (Vantiva SA)
• Inventors: Eskicioglu, Ahmet Mursit
• Application Number:
  US10/432,916
• Publication Number:
  US 20040047472A1
• Time in Patent Office: Days
• US Class Current: 380/277
• CPC Class Codes: H04L 9/085 Secret sharing or secret splitting, e.g. threshold schemes

Abstract

A method and apparatus for managing access to a signal representative of an event of a service provider, including receiving said signal in a smart card, said signal being scrambled using a scrambling key, receiving, in said smart card, data representative of a first share; constructing said scrambling key using said first share and at least one additional share, said additional share being stored in said smart card; and descrambling said signal using said constructed scrambling key to provide a descrambled signal, wherein the step of constructing said scrambling key comprises calculating the Y-intercept of the line formed on said Euclidean plane by said first, and said at least one additional share.

Claims

1. A method for managing access to a signal, said method comprising:

receiving, in a smart card, data representative of a first share;

constructing a symmetric scrambling key using said first share and at least two additional shares, said at least two additional shares being stored in said smart card; and

descrambling a signal using said constructed scrambling key to provide a descrambled signal.

2. The method of claim 1 wherein said first, second and third shares are points on a Euclidean plane.

8. The method of claim 1, wherein said first share and said at least two additional shares are points on at least a second degree polynomial function.

9. The method of claim 1, wherein the at least two additional shares comprise at least three additional shares, such that said first share and said at least three additional shares are points on at least a third degree polynomial function.

10. The method of claim 1, wherein the scrambling key comprises a secret value computed from the first and the at least two additional shares.

11. The method of claim 1, wherein the scrambling key comprises a function of a secret value computed from the first and the at least two additional shares

12. The method of claim 1, wherein the first share and the at least two additional shares comprise points on a polynomial function.

13. The method of claim 12, wherein the degree of the polynomial function is altered periodically.

14. The method of claim 1, comprising the further step of:

masking the first share before receiving the first share in the smart card.

15. The method of claim 14, comprising the further step of:

computing the first share from the masked version of the first share.

16. The method of claim 1, comprising the further step of:

transmitting a first share and at least one redundant share.

17. The method of claim 16, comprising the further step of:

filtering out said at least one redundant share after receiving said first share in said smart card.

3. A method for managing access to a signal representative of an event of a service provider, said method comprising:

receiving said signal in a smart card, said signal being scrambled using a symmetric scrambling key;

receiving, in said smart card, data representative of a first share;

constructing said scrambling key using said first share and second and third shares, said second and third shares being stored in said smart card; and

descrambling said signal using said constructed scrambling key to provide a descrambled signal,

wherein the step of constructing said scrambling key comprises calculating the Y-intercept of the curve formed on said Euclidean plane by said first, second and third shares.

4. The method of claim 3 wherein said first, second and third shares are points on a Euclidean plane.

5. The method of claim 3 wherein said smart card has a card body having a plurality of terminal pins arranged on a surface of said card body in accordance with one of ISO 7816 and PCMCIA card standards.

6. A system for managing access between a service provider and a device having a smart card coupled thereto, said device performing the steps of:

receiving a signal in a smart card, said signal being scrambled using a symmetric scrambling key;

receiving, in said smart card, data representative of a first share;

constructing said scrambling key using said first share and second and third shares, said second and third shares being stored in said smart card; and

descrambling said signal using said constructed scrambling key to provide a descrambled signal,

wherein the step of constructing said scrambling key comprises calculating the Y-intercept of the curve formed on said Euclidean plane by said first, second and third shares.

7. A conditional access system comprising:

at least one program service provider; and

,

a digital device including at least one smart card for receiving a scrambled signal and a first share transmitted by the at least one program service provider;

wherein said at least one smart card includes second and third shares stored therein for descrambling the scrambled signal, said second and third shares being used in conjunction with said first share to descramble said scrambled signal.

18. A method for operating a conditional access system comprising the steps of:

transmitting a scrambled signal and a first share from a service provider to a digital device;

receiving in the digital device said scrambled signal and said first share;

constructing a scrambling key using said first share and at least two additional shares, said at least two additional shares being stored in a smart card of the digital device; and

descrambling the signal using said constructed scrambling key to provide a descrambled signal.

19. A conditional access system comprising:

a transmitter; and

,

a receiver including at least one smart card for receiving a scrambled signal and a first share transmitted by the transmitter,

wherein said at least one smart card includes second and third shares stored therein for

descrambling the scrambled signal, said second and third shares being used in conjunction with said first share to descramble said scrambled signal.