Method for securing software updates

• US 20040107349A1
• Filed: 11/26/2003
• Published: 06/03/2004
• Est. Priority Date: 12/03/2002
• Status: Active Grant

• Current Assignee: Nagravision SA (Kudelski SA)
• Original Assignee: Nagravision SA (Kudelski SA)
• Inventors: Sasselli, Marco, Pican, Nicolas
• Granted Patent: US 7,440,571 B2
• Time in Patent Office: Days
• US Class Current: 713/176
• CPC Class Codes: H04L 2209/60 Digital content management, e.g. content distribution
• CPC Class Codes: H04L 9/0891 Revocation or update of secret information, e.g. encryption key update or rekeying
• CPC Class Codes: H04L 9/3236 using cryptographic hash functions
• CPC Class Codes: H04L 9/3247 involving digital signatures
• CPC Class Codes: H04N 21/2351 involving encryption of additional data arrangements using cryptography for the use of broadcast information or broadcast-related information H04H60/23
• CPC Class Codes: H04N 21/26291 for providing content or additional data updates, e.g. updating software modules, stored at the client deployment, distribution, installation, update of software G06F8/65; error detection or correction during software upgrading G06F11/1433; arrangements for updating broadcast information or broadcast-related information H04H60/25
• CPC Class Codes: H04N 21/63345 by transmitting keys key distribution for secret or secure communication H04L9/08; network support of key management H04L63/06
• CPC Class Codes: H04N 21/8166 involving executable data, e.g. software arrangements for executing specific programs G06F9/44; broadcasting computer programmes in broadcast systems H04H20/91; involving the movement of software or configuration parameters H04L67/34
• CPC Class Codes: H04N 7/16 Analogue secrecy systems; Analogue subscription systems

Abstract

This invention proposes a method for securing updating software in a plurality of decoders based on the generation of a signature by means of a private asymmetrical key. The updating of a decoder is carried out by downloading, from a managing center, a data block including a patch and its signature, said block is stored in a RAM. The signature is decrypted with a current public key from a list contained in a first non-volatile memory of the decoder, then verified and in the case of correspondence, a command leads the installation of the patch in a second non-volatile Flash memory and the deactivation of the current key. The aim of this invention is to considerably reduce the impact of the discovery of a private key by mean of a systematic analysis of the working of the decoder software, or to notably increase the time and the means necessary for the process used to determine said private key.

Claims

1. Method for securing updating data from a plurality of apparatuses, each apparatus receiving the updates from a managing center, these updates including data called patch accompanied by a control block encrypted by a private asymmetrical key taken from a list of keys included in the managing center, characterized by following steps:

selection by means of the apparatus of a current key from a list of public keys,

reception and storage in the memory of the updating patch,

reception of the encrypted control block,

decryption of said block by the current public key,

verification that the decrypted control block corresponds to said patch,

installation of the patch received,

deactivation of the current key and selection of the next key in the list.

2. Method according to claim 1 wherein the control block includes a signature on the patch data, this signature being the result of a hash function.

3. Method according to claims 1 and 2 wherein the verification of the block includes the step of establishing the signature on the received patch and the comparison with the decrypted signature in the control block.

4. Method according to claim 1 wherein the control block includes a symmetrical session key determined by the managing center, this key being used to encrypt the patch data.

5. Method according to claim 1 wherein, for each update, a new public key taken from the list is used by the apparatus.

6. Method according to claim 1, wherein the public key is deleted from the list after being used, said key being useless for the next updates.

7. Method according to claim 1, wherein the public keys of the list are used sequentially in a predetermined order during each update.

8. Method according to claim 1 wherein the list of public keys is stored in a non-volatile memory, a key used for an update is definitively deleted from the memory that authorizes the access to the next key for the subsequent update.

9. Method according to claim 1 wherein, for the updating of the software of an apparatus of a certain version to a new version, with a difference between the new version and the previous one greater than one, at least one message encrypted with a private key is added allowing the changing of the current key to the next key in the list, the successful decryption of said message inducing the deactivation of the current key and the selection of the next key.

10. Method according to claim 9, wherein the number of messages corresponds to the number of updates separating the initial version of the apparatus and the final version of the update.

11. Method according to claim 1, wherein an updating installation is followed by an increment on a counter or by moving a pointer indicating the position of the key to be selected from the list during the subsequent update, while the list of keys remains unchanged.

12. Method according to claim 1, wherein the control block is successively encrypted by the keys of the previous updates, each key from the list being used one after the other to decrypt the signature.

13. Method according to claim 1, wherein the apparatuses consist of Pay-TV decoders, an update of a decoder being carried out by downloading, from a managing center, of a patch accompanied by a control block, said block is stored in a Random Access Memory, and is decrypted with a current public key contained in a first non-volatile memory of the decoder, then verified and in the case of correspondence, a command leads the installation of the patch in a second non-volatile memory and the deactivation of the current key.

14. Method according to claim 13, wherein a new list of public keys is transmitted to the decoder, said list replaces the list contained in the first memory containing keys deactivated by previous successful updates.