Security key generation method

• US 20040236959A1
• Filed: 05/19/2004
• Published: 11/25/2004
• Est. Priority Date: 05/23/2003
• Status: Active Grant

• Current Assignee: Nagravision SA (Kudelski SA)
• Original Assignee: Nagravision SA (Kudelski SA)
• Inventors: Kudelski, Henri, Gaumain, Serge
• Granted Patent: US 7,725,740 B2
• Time in Patent Office: Days
• US Class Current: 713/193
• CPC Class Codes: G06Q 20/341 Active cards, i.e. cards including their own processing means, e.g. including an IC or chip
• CPC Class Codes: G06Q 20/40975 using encryption therefor
• CPC Class Codes: G07F 7/1008 Active credit-cards provided with means to personalise their use, e.g. with PIN-introduction/comparison system
• CPC Class Codes: G07F 7/1016 Devices or methods for securing the PIN and other transaction-data, e.g. by encryption arrangements for secret communication, see H04L9/00

Abstract

A method is used to restore the security of a secure assembly such as a chip card, after the contents of its second memory zone have been read by a third party. The method is for generating a security key implemented by a secure module comprising a central unit, a first conditional access memory zone and at least one second memory zone containing all or part of the user program. The method includes reading of all or part of the second memory zone, and generation of at least one root key based on all or part of the second zone data and on at least one item of secret information stored in the first memory zone.

Claims

1. Method for generating a security key implemented by a secure module comprising a central unit, a first conditional access memory zone and at least one second memory zone containing all or part of the user program, wherein this method includes the following steps:

reading of all or part of the second memory zone,

generation of at least one root key based on all or part of the data of the second zone and on at least one item of secret information stored in the first memory zone.

2. Method according to claim 1, wherein the secret information is a factory key.

3. Method according to claim 1, wherein the secret information is an algorithm describing the use of the data to generate the root key.

4. Method according to claim 1, wherein it consists in calculating at least one item of control information representative of all or part of the data of the second zone, this control information being used for the generation of the root key.

5. Method according to claim 4, wherein the control information is the result of a function (Hash) called unidirectional and without collision, executed on all or part of the data of the second memory zone.

6. Method according to claim 1, wherein the second zone includes furthermore a description part comprising the location of the memory zone(s) determining the formation of the control information.

7. Method according to claim 6, wherein this description part includes a plurality of location information for each part of the user memory zone corresponding to partial control information.

8. Method according to claim 2, wherein the factory key is of the symmetrical type.

9. Method according to claim 1, wherein the second zone includes a verification zone and a user zone, the programs contained in the verification zone are in charge of the verification of the data in the user zone, the program system of the first zone transferring the necessary data from this first zone towards the verification zone.

10. Method according to claim 9, wherein the factory key is copied from the first zone towards the verification zone by the system program.

11. Method according to claim 10, wherein the factory key is eliminated when the root key is generated.

12. Method according to claim 1, wherein the root key is used as the transmission key to decrypt the messages originating from a management centre.