Method for transmitting messages between an emitter and at least on receiver and system for implementing said method

• US 7,724,896 B2
• Filed: 12/09/2005
• Issued: 05/25/2010
• Est. Priority Date: 12/10/2004
• Status: Active Grant

• Current Assignee: Nagra France Sàrl (Kudelski SA)
• Original Assignee: Nagra France Sàrl (Kudelski SA)
• Inventors: Nimour, Abdelkrim, Bredy, Nicolas, Barbier, Eve-Marie
• Primary Examiner(s): SMITHERS, MATTHEW
• Application Number:
  US11/297,637
• Publication Number:
  US 20060140397A1
• Time in Patent Office: 1,628 Days
• Field of Search: 380/264
• US Class Current: 380/28
• CPC Class Codes: H04L 2209/76 Proxy, i.e. using intermediary entity to perform cryptographic operations network architectures or network communication protocols using hop-by-hop encryption H04L63/0464
• CPC Class Codes: H04L 9/3013 involving the discrete logarithm problem, e.g. ElGamal or Diffie-Hellman systems
• CPC Class Codes: H04L 9/3066 involving algebraic varieties, e.g. elliptic or hyper-elliptic curves
• CPC Class Codes: H04N 21/2343 involving reformatting operations of video signals for distribution or compliance with end-user requests or end-user device requirements video transcoding H04N19/40; media packet handling at the source H04L65/762
• CPC Class Codes: H04N 21/2347 involving video stream encryption
• CPC Class Codes: H04N 21/4405 involving video stream decryption
• CPC Class Codes: H04N 7/1675 Providing digital key or authorisation information for generation or regeneration of the scrambling sequence pseudo-random number generators in general G06F7/58

Abstract

Example embodiments relate to a method and system for transmitting messages between an emitter and at least one receiver. The method may include encrypting a message (m) to be transmitted by means of a key (a) associated to the emitter, sending the encrypted message to a conversion module including at least a conversion key (π_a→b) and a conversion function, the conversion module being placed between the emitter and the at least one receiver, converting the encrypted message received in the conversion module by at least one message encrypted in such a way as to be able to be decrypted by a key (b) specific to the at least one receiver, the conversion being carried out without the initial message appearing in plaintext in the conversion module, and resulting in as much messages in accordance to a number of receivers, sending the converted message to a certain receiver, and decrypting the converted message received by the certain receiver via the key b specific to the receiver, wherein the conversion key (π_a→b) of the conversion module depends on a non trivial value raised to a power of the key (a) bound to the emitter and of the key (b) bound to the at least one receiver.

Claims

1. A method for transmitting messages between an emitter and at least one receiver, comprising:

encrypting a message (m) to be transmitted by means of a key (a) associated to said emitter;

sending the encrypted message to a conversion module including at least a conversion key (π

<sub>a→

b</sub>) and a conversion function, said conversion module being placed between the emitter and said at least one receiver;

converting the encrypted message received in the conversion module by at least one message encrypted in such a way as to be able to be decrypted by a key (b) specific to said at least one receiver, the conversion being carried out without the initial message appearing in plaintext in the conversion module, and resulting in as much messages in accordance to a number of receivers;

sending the converted message to a certain receiver; and

decrypting said converted message received by said certain receiver via the key b specific to said receiver;

wherein the conversion key (π

<sub>a→

b</sub>) of the conversion module depends on a non trivial value raised to a power of the key (a) bound to the emitter and of the key (b) bound to the at least one receiver.

2. The method according to claim 1, wherein the message (m) to be transmitted is a content (CT).

3. The method according to claim 1, wherein the message (m) to be transmitted is an authorization message containing at least one control word (cw) having served to encrypt a content (CT).

4. The method according to claim 1, wherein the key (π

<sub>a→

b</sub>) of the conversion module is equal to

5. A system for transmitting messages between an emitter and at least one receiver, said emitter including means to encrypt a message (m) by means of a key (a) associated to the emitter, said system comprising:

at least one conversion module in which at least a conversion key (π

<sub>a→

b</sub>) and a conversion function are memorized, the at least one conversion module being placed between the emitted and said at least one receiver and further being arranged to convert the input message (m) into at least one message which is able to be decrypted by a key (b) specific to said at least one receiver,

the at least one receiver including a decryption stage arranged to decrypt the output message of the at least one conversion module, wherein the conversion key (π

<sub>a→

b</sub>) of the at least one conversion module depends on a non trivial value raised to a power of the key (a) bound to the emitter and of the key (b) bound to the at least one receiver.

6. A system for transmitting messages according to claim 5, wherein the conversion key is

7. The system for transmitting messages according to claim 5, wherein the at least one conversion module is contained in said at least one receiver.

8. The system for transmitting messages according to claim 5, wherein the at least one conversion module is contained in a retransmission center distinct from said at least one receiver, and remotely connected to the at least one receiver.

9. A system for transmitting messages between an emitter and at least one receiver, said emitter including a device to encrypt a message (m) by a key (a) associated to the emitter, said system comprising:

at least one conversion module in which at least a conversion key (π

<sub>a→

b</sub>) and a conversion function are memorized, the at least one conversion module being placed between the emitted and said at least one receiver and further being arranged to convert the input message (m) into at least one message which is able to be decrypted by a key (b) specific to said at least one receiver,

the at least one receiver including a decryption stage arranged to decrypt the output message of the at least one conversion module, wherein the conversion key (π

<sub>a→

b</sub>) of the at least one conversion module depends on a non trivial value raised to a power of the key (a) bound to the emitter and of the key (b) bound to the at least one receiver.