FR2907287A1 - Private content i.e. audio-video type data flow, transmitting method for set top box and digital TV, involves transmitting content to destination node, and associating password to content to condition access of parameters - Google Patents

Abstract

The method involves receiving parameters associated to a key during a phase of exchanging the parameters between a source device/terminal i.e. set top box (100), and a source node (101) i.e. network access point. A private content i.e. audio-video type data flow, encrypted with the key, is received by the node during a transmission phase between the device/terminal and the node. The content encrypted with the key is transmitted to a destination node (104) by the node (101). A password is associated to the content for permitting conditioning of an access of the parameters by the node (104). Independent claims are also included for the following: (1) a method for receiving a private content (2) a downloadable computer program product comprising instructions to perform a method for transmitting a private content (3) a storage medium comprising instructions to perform a method for transmitting a private content (4) a source node for transmitting a private content between source and destination devices (5) a destination source for receiving a private content by a destination device.

Description

1 Methods of secure transmission of content, including

  restriction of access to this content, product computer program, storage medium, and corresponding devices. FIELD OF THE INVENTION The field of the invention is that of data communication networks. More particularly, the invention relates to the protection of contents transmitted between several terminals via such a network. The invention applies in particular, but not exclusively, in the case where the content is an audio-video (AV) type data stream transmitted over a multimedia network. 2. PRIOR ART There are content protection protocols based on device authentication and content exchange encrypted between these devices. For example, there is known the DTCP protocol (for Digital Transmission Content Protection in English and protection of contents in digital transmission in French). The characteristics and recommendations of this protocol are detailed in the following reference document: Digital Transmission Content Protection Specification, Volume 1 and 2, Draft 1.29. With these protocols, only authenticated devices can decrypt the content. However, these protocols allow device-level authentication, but not access restriction at the content level. Indeed, once a first device has authenticated with a second device, the first device can access all available contents in or through the second device, and vice versa.

  However, there is a need to restrict access to certain content available in or through a device, particularly when this device is interconnected to a plurality of other devices all authenticated to each other by a content protection protocol.  This restriction is particularly useful for providing a private content management service that only allows certain users access to certain content in the communication network interconnecting the devices.  2907287 2 There exist in the state of the art methods for managing the private nature of a content by applying a double encryption: - a first end-to-end encryption, with a first key, applied between the device source and the destination device.  On the source side, the user provides, via an interface of the source device, information for determining the first key, or the first key itself.  Destination side, the user provides, via an interface of the recipient device, the same information, so that the recipient device has the first key; and a second encryption, according to a content protection protocol (DTCP for example) and with a second key, applied between the authenticated intermediary devices which are on the path between the source and destination devices.  These intermediate devices are the network nodes through which the source and destination devices are interconnected.  Thus, the content is received by the destination device with only the first encryption, the second encryption having been removed (eg by the last node before the destination device).  These known methods have a major disadvantage: the recipient device, which may be for example a display device, must have an interface allowing the user to enter information used to determine the first key, or the first key itself.  Indeed, this is imperative so that the encrypted content with the first key is exploited (that is to say read) by the recipient device.  Another disadvantage of these known methods is that it is not possible to use any recipient device available in the market (eg a digital television) because it must have the means to handle double decryption.  Yet another disadvantage of known methods is that the source device must also contain means for managing double encryption.  It is therefore not possible to use any source device available on the market and to ensure the private broadcast of the content.  30 3.  OBJECTIVES OF THE INVENTION The invention, in at least one embodiment, is intended in particular to overcome these various disadvantages of the state of the art.  More specifically, it is an object of the present invention, in at least one embodiment, to provide a technique for securely transmitting content between a source device and a recipient device, allowing access restriction to this content, without the recipient device has an interface allowing the user to enter information used to determine a key, or the key itself, and has to manage a double decryption.  The invention also aims, in at least one embodiment, to provide such a technique of secure transmission of content between a source device and a destination device, allowing access restriction to this content, without as far as the source device does not have an interface allowing the user to enter information used for the determination of a key, or the key itself, and has to manage a double encryption.  Another object of the invention, in at least one embodiment, is to provide such a technique which is simple to implement and inexpensive.  4.  DISCLOSURE OF THE INVENTION In a first particular embodiment of the invention, on the source side, there is provided a method of securely transmitting private content between a source device and at least one destination device through a source node to which the source device is connected and at least one destination node to which the at least one destination device is connected, said source device and source node using a content protection protocol having a key parameter exchange phase and a content transmission phase encrypted with the key associated with the key parameters exchanged.  This method comprises the following steps: reception by the source node of parameters associated with a first key during said phase of exchange of key parameters between the source device and the source node; receiving the source node encrypted content with said first key during said transmission phase between the source device and the source node; - transmission by the source node encrypted content at least with the first key auditing at least one destination node; and associating a password with the private content, making it possible to condition the access by said at least one destination node to the key parameters associated with the first key.  It is important to note that in this first embodiment, the source node does not decrypt the encrypted content with the first key, which comes from the source device, before transmitting it to the destination node (s).  In addition, a password is associated with the private content.  As explained later, this password is provided to at least one third party entity.  By third entity, for example means a user or a controller node.  This first embodiment is transparent to the source device.  Thus, and as explained below, subject to obtaining this password beforehand (by the destination node or the controller node), the parameters of the first key are then determined by the destination node which, on the destination side, transmits them to the destination device during the key parameter exchange phase of the content protection protocol.  In addition, this destination node receives the encrypted content with the first key and then transmits it to the destination device during the encrypted content transmission phase of the content protection protocol.  This ensures that the content remains encrypted with the first key from the source device to the destination device (therefore end-to-end), without the destination device having an interface allowing a user to enter information used to determine the first key, or the first key itself, and have to handle a double decryption.  In other words, it is possible to manage the privacy of a content, only the provision of the parameters of the first key (for example by a user, in the form of a password) to access to the content in the clear.  In a first example of the first embodiment, the step of associating a password with the private content is performed by a controller node in charge of establishing a connection between the source device and the destination device for the purpose. Transmission of the private content, said step of associating a password with the private content comprising the following steps: receiving the parameters associated with the first key and transmitted by the source node; 5 - exchange, through a user interface of the controller node, the password with a user, the password being defined by the controller node or the user; storage of the password in an association table comprising an identifier of said content, said password and the key parameters associated with the first key.  Thus, for at least one destination node given (for example if it is involved in an additional connection), the subsequent provision to the controller node of the password by the user authorizes the controller node to transmit to said at least one destination node the key parameters associated with the first key.  Advantageously, the password is defined by the controller and said password is obtained by using the key parameters associated with the first key.  In a second example of the first embodiment, the step of associating a password with the private content is performed by the source node and comprises the following steps: - generation of the password using the key parameters associated with the first key; and - providing the password to a user, through a user interface of the source node.  Thus, the subsequent provision of the password to a destination node given by the user enables said given destination node to retrieve the key parameters associated with the first key.  In a third example of the first embodiment, the step of associating a password with the private content is performed by the source node and comprises the following steps: - generating the password using the key parameters associated with the first key; and 2907287 6 - providing the password to a controller node in charge of establishing a connection between the source device and the destination device for the transmission of the private content.  The method further comprises the following step, performed by the controller node: providing, through a user interface of the controller node, the password to a user.  Thus, for at least one destination node given (for example if it is involved in an additional connection), the subsequent provision to the controller node of the password by the user authorizes the controller node to transmit the password to said 10 to least one destination node and thus allows said at least one destination node to find the key parameters associated with the first key.  Advantageously, said password is the result of a bijective function applied to the key parameters associated with the first key.  In a fourth example of the first embodiment, the step of associating a password with the private content is performed by the source node and comprises the following steps: -generation of the password using the key parameters associated with the first key; providing the password to a controller node in charge of establishing a connection between the source device and the destination device for the transmission of the private content.  The method further comprises the following steps, performed by the controller node: - exchanging, through a user interface of the controller node, a second password with a user, said second password being defined by the controller node or the user; storing said second password in an association table comprising an identifier of said content, said password and said second password.  Thus, for at least one destination node given (for example if it is involved in an additional connection), the subsequent provision to the controller node of said other password by the user authorizes the controller node to transmit to the at least 2907287 7 a destination node given said password, and thus allows said at least one destination node to retrieve the key parameters associated with the first key.  Advantageously, the method further comprises the following steps: encrypting with a second key, by the source node, the encrypted content with the first key, in order to obtain a doubly encrypted content; transmission by the source node of parameters associated with the second key, during a phase of exchange of key parameters between the source node and the said at least one destination node; and -transmission of the doubly encrypted content, during the step of transmission by the source node of the encrypted content at least with the first key.  In a second particular embodiment of the invention, on the destination side, there is provided a method for the secure reception of a private content by at least one destination device through at least one destination node to which the at least one destination device is connected, said destination device and destination node 15 using a content protection protocol having a key parameter exchange phase and an encrypted content transmission phase with the key associated with the exchanged key parameters.  This method comprises the following steps: reception by said at least one destination node of the private content, previously encrypted with a first key and coming from a source device through a source node to which said source device is connected; - obtaining a password associated with the private content; determination of the key parameters associated with said first key, by the use of the password obtained in the obtaining step; transmission by said at least one destination node of said key parameters to the destination device during said key parameter exchange phase between the destination node and the destination device; and transmitting the encrypted content with the first key received at the receiving step at the destination device.  It is important to note that the destination node does not have a usual operation since, in its communication with the destination device, according to the content protection protocol: - in the key exchange phase, it transmits to the device destination the parameters of the first key, and not the parameters of a key specific to this communication with the destination device; before the encrypted content transmission phase, it does not encrypt the content 5 (already encrypted with the first key) with a key specific to this communication with the destination device.  This technique according to the invention is therefore implemented in a transparent manner for the destination device.  Indeed, the destination device behaves as if it were communicating in the usual way, according to the content protection protocol (for example DTCP), with a source device.  However, in reality, the destination node is not the source device (the source device is the one that performs the first encryption, with the first key).  Thus, and as already indicated above, this makes it possible to guarantee that the content remains encrypted with the first key from the source device to the destination device (therefore from end to end), without the destination device having any an interface allowing a user to enter information used to determine the first key, or the first key itself, and has to manage a double decryption.  In a first example of the second embodiment, the step of obtaining a password and the step of determining the key parameters associated with said first key are performed by said at least one destination node.  The step of obtaining a password is performed by the entry of said password by a user, through a user interface of said at least one destination node.  In a second example of the second embodiment, the step of obtaining a password and the step of determining the key parameters associated with said first key are performed by a controller node in charge of establishing a password. connection between the source device and the destination device for receiving the private content.  The step of obtaining a password is performed by the entry of said password by a user, through a user interface of said controller node.  The step of determining the key parameters is performed by reading, from the password obtained in the obtaining step, an association table comprising an identifier of said content, said password. and the key parameters associated with the first key.  The method further comprises a step of transmitting to said at least one destination node, by the controller node, parameters determined in the determination step.  In a third example of the second embodiment, the step of obtaining a password is performed by a controller node in charge of establishing a connection between the source device and the destination device for receiving the private content. said step of obtaining a password being effected by the entry of said password by a user, through a user interface of said controller node.  The method further comprises a step of transmitting to said at least one destination node, by the controller node, the password obtained in the obtaining step.  The step of determining the key parameters is performed by said at least one destination node from the password transmitted by the controller node. According to an advantageous characteristic, the password obtained in the obtaining step is the result of a bijective function applied to the key parameters associated with the first key and in that the step of determining the associated key parameters to the first key is performed by applying the inverse function of the bijective function to said password.  In a fourth example of the second embodiment, the step of obtaining a password is performed by a controller node in charge of establishing a connection between the source device and the destination device for receiving the private content. said step of obtaining a password comprising the steps of: - obtaining a second password by inputting said second password by a user, through a user interface of said controller node; - Determining said password by reading from said second password, an association table comprising an identifier of said content, said password and said second password.  In addition, the method further comprises a step of transmitting to said at least one destination node, by the controller node, of the password obtained in the step of determining said password.  The step of determining the key parameters is performed by said at least one destination node from the password transmitted by the controller node.  Advantageously, the content received by the destination node is doubly encrypted with the first key and a second key and the method further comprises the following steps: a step of authentication and exchange of key parameters associated with the second key between the source node and the destination node; anddecrypting, with the second key, the doubly encrypted content, in order to obtain the encrypted content only with the first key.  In another embodiment, the invention relates to a computer program product downloadable from a communication network and / or recorded on a computer readable medium and / or executable by a processor.  This computer program product includes program code instructions for performing the steps of the aforementioned secure transmission method and / or the aforementioned secure receiving method, when said program is run on a computer.  In another embodiment, the invention relates to a storage medium, possibly totally or partially removable, readable by a computer, storing a set of instructions executable by said computer to implement the above mentioned secure transmission method and / or the aforementioned secure reception method.  In another embodiment, the invention relates to a source node capable of participating in the secure transmission of private content between a source device and at least one destination device through said source node to which the source device is connected and at least one a destination node to which said at least one destination device is connected, said source device and source node using a content protection protocol having a key parameter exchange phase and an encrypted content transmission phase with the key associated with the parameters key exchange.  This source node comprises: means for receiving parameters associated with a first key during said key parameter exchange phase between the source device and the source node; Means for receiving the encrypted content with said first key during said transmission phase between the source device and the source node; means for transmitting the encrypted content at least with the first key to said at least one destination node, a password being associated with the private content, making it possible to condition the access by said at least one destination node to the associated key parameters at the first key.  In a first exemplary embodiment of the source node, the latter comprises means for transmitting the parameters associated with the first key to a controller node in charge of establishing a connection between the source device and the destination device 10 for the transmission of the content. private, so that said controller node performs the association of a password to the private content.  Advantageously, to perform the association of a password to the private content, the source node comprises: password generation means using the key parameters associated with the first key; and - means for providing the password to a user, through a user interface of the source node.  In a second exemplary embodiment of the source node, the latter comprises, for effecting the association of a password with the private content: means for generating the password by using the key parameters associated with the first key; and - means for providing the password to a controller node in charge of establishing a connection between the source device and the destination device for the transmission of the private content, so that the controller node provides, through a user interface of the controller node, the password to a user.  Advantageously, said password is the result of a bijective function applied to the key parameters associated with the first key.  In a third exemplary embodiment of the source node, the latter comprises, for effecting the association of a password with the private content: means for generating the password by using the key parameters associated with the first key; - means for supplying the password to a controller node in charge of establishing a connection between the source device and the destination device for the transmission of the private content, so that the controller node: * exchanges, through an interface controller node user, a second password with a user, said second password being defined by the controller node or the user; stores said second password in an association table comprising an identifier of said content, said password and said second password.  In a fourth embodiment of the source node, it comprises: encryption means with a second key encrypted content with the first key, in order to obtain a doubly encrypted content; means for transmitting parameters associated with the second key, during a phase of exchange of key parameters between the source node and the said at least one destination node.  In addition. said encrypted content transmission means at least with the first key transmit said doubly encrypted content.  In another embodiment, the invention relates to a destination node capable of participating in the secure reception of private content by at least one destination device through at least said destination node to which said at least one destination device is connected, said device destination and destination node using a content protection protocol having a key parameter exchange phase and an encrypted content transmission phase with the key associated with the key parameters exchanged.  This destination node comprises: means for receiving the private content, previously encrypted with a first key and coming from a source device through a source node to which said source device is connected; means for receiving or determining the key parameters associated with said first key, said key parameters being determined by the use of a password associated with the private and previously obtained content; Means for transmitting said key parameters to the destination device during said key parameter exchange phase between the destination node and the destination device; and means for transmitting to the destination device the encrypted content with the first key received by the reception means.  In a first embodiment of the destination node, the latter comprises: means for obtaining said password, by inputting said password by a user, through a user interface of said at least one destination node; and means for determining the key parameters associated with said first key from the password obtained.  In a second exemplary embodiment of the destination node, the latter comprises means for receiving the key parameters associated with said first key, said key parameters being determined and transmitted by a controller node in charge of establishing a connection between the source device and destination device for receiving private content.  In a third exemplary embodiment of the destination node, the latter comprises: means for receiving said password obtained by a controller node in charge of establishing a connection between the source device and the destination device for the reception of the private content ; and - means for determining the key parameters associated with said first key, from the received password.  Advantageously, the password obtained is the result of a bijective function applied to the key parameters associated with the first key, and the means for determining the key parameters associated with the first key apply the inverse function of the bijective function audit. password.  Advantageously, the content received by the destination node is doubly encrypted with the first key and a second key and the destination node comprises: means for authenticating and exchanging key parameters associated with the second key, between the source node and the destination node; and decrypting means, with the second key, of the doubly encrypted content, in order to obtain the encrypted content only with the first key.  5.  LIST OF FIGURES Other characteristics and advantages of embodiments of the invention will appear on reading the following description of a preferred embodiment of the invention, given by way of indicative and nonlimiting example ( all the embodiments of the invention are not limited to the features and advantages of this preferred embodiment), and the accompanying drawings, in which: FIG. 1 shows the diagram of an example of a home audio-video network 10 in which the invention can be implemented; FIG. 2 presents a flowchart of the DTCP protocol when transmitting content between a source device and a receiving device; FIG. 3 shows the block diagram of a node of the home network of FIG. 1, according to a particular embodiment of the invention; FIG. 4 shows a flowchart of a particular embodiment of a method according to the invention for the secure transmission of a content, from a source terminal to a backbone network, in the context of FIG. 1; FIG. 5 presents a flowchart of a particular embodiment of a method according to the invention for the secure transmission of a content, from the backbone network to a destination terminal, in the context of FIG. 1; FIG. 6 presents a flowchart of a particular embodiment of a method according to the invention for the secure transmission of a content, as implemented in a controller node; and FIG. 7 presents a flowchart of a particular embodiment of a method according to the invention of a second secure transmission of a content, as implemented in a controller node.  6.  DETAILED DESCRIPTION It is considered in the following that the content protection protocol implemented is the aforementioned DTCP protocol.  However, it is obvious that the invention also applies to any content protection protocol comprising an encryption key exchange phase and an encrypted content transmission phase.  In the following description, in the context of the home audio-video network 1000 of FIG.  It is clear however that the invention can be implemented in any communication network.  The home network 1000 comprises a backbone network 106 which itself comprises nodes 101, 102, 104, 112 interconnected by digital links.  The nodes 101, 102, 104, 112 may also be called network access points (or Network Access Point), and hence are hereinafter designated by NAPO, NAP1, NAP2 and NAP3 respectively.  The nodes are connected audio-video equipment 100, 103, 105, 110 through digital links 107, 108, 109, 111, which can be complemented by analog links (not shown), as described in the document. reference on the CEA-775 standard entitled DTV 1394 Interface Specification, for example to allow the display of graphic information or man-machine interface on the TVs 105 and 110, this graphic information can come from either audio-video equipment 100 and 103 are nodes 101, 102, 104, 112 of the home network 1000.  The digital links that interconnect the nodes to one another or the equipment to the nodes may be compliant by way of non-limiting example to the IEEE 1394 standard (described in the IEEE Std.  1394-1995, Standard for High Performance Serial Bus, IEEE Standard 1394a-2000, Standard for High Performance Serial Bus (Supplement) and IEEE P1394. 1 Draft 0. 15, Standard for 20 High Performance Serial Bus Bridges), to the IEEE 802 Ethernet standard. 3, or the IEEE 802 radio communication standard. 11.  In the example illustrated in FIG. 1, it is assumed that: a Set Top Box (or STB) 100, used as the source terminal, is connected to the NAPO node 101 via a referenced IEEE 1394 bus 107; a digital television (or DTV, for Digital TV in English) 105, used as destination terminal, is connected to the NAP2 node 104, via an IEEE 1394 bus referenced 109; A digital television (or DTV, for Digital TV in English) 110, used as the second destination terminal, is connected to the node NAP3 112, via an IEEE bus, 1394 referenced 111; a digital audio-video hard disk drive (or HDD, for Hard Disk 5 Drive in English) 103, used as a storage device, is connected to the NAP1 node 102, via an IEEE 1394 bus referenced 108.  In the remainder of the description, the following first example of two-step operation is used for explanatory purposes: first of all (phase described hereinafter with reference to FIG. 4), a user 10 wishes that a content received by the set-top box 100 is transmitted and stored securely in the digital hard disk drive 103; and then (phase described below in connection with FIG. 5), this user wants the content stored by the digital hard disk player 103 to be transmitted securely to the digital television 105.  It is clear that the present invention is also applicable if the source terminal and the destination terminal are connected to the same node (in other words, the source node and the destination node may be merged).  For example, by repeating and modifying the previous example, the set-top box STB 100 and the digital television DTV 105 could be connected to the same node (eg NAPO).  In the remainder of the description, a second example of operation is also used for explanatory purposes in the case of a transmission without intermediate storage (for example in the form of a real time reading, also known as streaming in English) where a user wants content received by the set-top box STB 100 to be directly transmitted securely to the DTV digital television 105.  The secure content transmission methods according to the invention are for example implemented in the form of software and / or a plurality of sub-software (comprising a plurality of algorithms, for example those described below). in relation to FIGS. 4 and 5) which is (are) executed in several nodes of the network 1000.  FIG. 2 shows the implementation of the DTCP protocol when transmitting content between a source device referenced A (for example the set-top box STB 100). , and a receiver device, referenced B (for example the source node NAPO 101).  The conventional DTCP protocol comprises a mutual authentication phase 200 of the receiver device B and the source device A, followed by a key exchange phase 210 between these two devices A and B and content encryption / decryption.  The authentication phase 200 comprises the following steps: in a first step 201, the receiving device B sends an authentication request, comprising authentication information of the receiving device B, which it sends to the source device A; in a second step 202, the source device A checks the authentication information of the receiver device B; in a third step 203, the source device A sends to the receiver device B a response message to the aforementioned authentication request, comprising authentication information of the source device A; in a fourth step 204, the receiving device B checks the authentication information of the source device A; in a fifth step 205, the source device A sends to the receiver device B a first signed message including information specific to the DTCP protocol; in a sixth step 206, the receiver device B controls the first signed message of the source device A and calculates a first authentication key (Kauth); in a seventh step 207, the receiving device B in turn sends, to the source device A, a second signed message including information specific to the DTCP protocol; in an eighth step 208, the source device A controls the second signed message of the receiver device B and calculates a second authentication key (Kauth ').  The phase 210 of key exchange and content encryption / decryption comprises the following steps: in a ninth step 211, the source device A generates random information, for example a random number Nc, calculates a key of exchange Kx and calculates an encryption key Kc which is a function notably of the random number Nc and which satisfies Kc = J [Kx, EMI, Nc], where J is a determined function, Kx the exchange key and EMI a classical parameter of DTCP protocol; in a tenth step 212, the random number Nc and the exchange key Kx are sent securely (i.e. in encrypted form) by the source device A to the receiver device B; in an eleventh step 213, the receiver device B calculates the encryption key Kc by means of the random number Nc and the exchange key Kx; in a twelfth step 214, the source device A encrypts the content 15 with the encryption key Kc (by applying a function fKc), so as to obtain an encrypted content denoted Msa; in a thirteenth step 215, the source device A sends the encrypted content Msa to the receiver device B; in a fourteenth step 216, the receiving device B decrypts the encrypted content Msa by means of the encryption key Kc (by applying a function f-'Kc which is the reciprocal function of the function fKc).  In connection with FIG. 3, a particular embodiment of a node 300 compatible with the secure transmission methods of the invention is presented.  This generic node 300 corresponds to any one of the nodes NAPO 101, NAP1 102, NAP2 104 and NAP3 112 of FIG. 1, considering that each of these nodes can play, depending on the case, the role of a node. source node or a destination node.  It is clear, however, that some nodes may be specialized and play only some of these roles.  The node 300 is connected to both backbone 106, via one or more Ethernet links 314, and to one or more terminals (e.g., a set top box 2907287 19 STB, a digital television DTV or a digital hard disk player HDD ), via a digital bus 313 (IEEE 1394 link).  The node 300 comprises: a first interface module 301 with the digital bus 313; 5 - a second interface module 312 with the Ethernet link (s) 314; a first FIFO (First In First Out) module for sending / receiving 302, connected to the first interface module 301; a second transmission / reception FIFO module 315, connected to the second interface module 312; a first encryption / decryption module 304 implementing encryption and decryption algorithms in accordance with the DTCP protocol, and placed between the sending / receiving FIFO module 302 and the sending / receiving FIFO module 305; A second encryption / decryption module 311 implementing encryption and decryption algorithms in accordance with the DTCP protocol, and placed between the sending / receiving FIFO module 305 and the transmitting / receiving FIFO module 315; a third transmission / reception FIFO module 305, connected to the first 304 and second 311 encryption / decryption modules; a FIFO management module 303, making it possible to control the accesses (read and write) to the FIFOs 302, 305 and 315, in accordance with the requests of a bridge manager module 306; a DTCP control module 307, implementing the DTCP protocol and connected to the first 304 and second 311 encryption / decryption modules, enabling the activation and / or deactivation of the encryption / decryption means of the first 304 and second 311 modules for a given flow transiting between the interface 301 and the interface 312; a microprocessor 109 (or CPU, for Central Processing Unit in English); A memory block 110 (or EPROM, for Erasable Programmable Read Only Memory in English), connected to the microprocessor 109; a third interface module 308 with the microprocessor 109, connected to the DTCP control module 307 and to the bridge manager module 306.  In connection with the flowchart of FIG. 4, a particular embodiment of a method according to the invention for the secure transmission of a content, from a source terminal to the backbone, is presented in the context of FIG. Figure 1.  Recall that in the illustrative example considered, it is assumed that the user 10 wishes that a content received by the set-top box STB 100 (source terminal) is

  transmitted and stored securely in the HDD hard disk drive 103 (storage device), via NAPO nodes 101 (source node) and NAP1 102 (destination node). In a step referenced 401, the NAPO source node receives a request from a controller requesting the transmission and storage of private content (i.e., a private stream) from the STB set-top box 100 to the reader. HDD 103 HDD. By specifying that the content is private, the controller tells the NAPO source node that it must implement the method according to the invention, ensuring a secure transmission end-to-end of this content (not only between nodes, but also until reception by the destination terminal, that is to say the digital TV DTV 105 in the example, see Figure 5). The steps implemented by the controller, which is a node of the network 1000 which serves as an interface with the user, which allows control of the various network equipment and which allows the communication of said equipment, will be explained later in relation with the flowchart 25 of FIG. 6. In a step referenced 402, the source node NAPO determines whether the stream is already in progress, that is, if the stream connection is already established between the source terminal STB 100 and the NAPO node 101. It should be noted that if a connection is already established, it is considered not to be private within the meaning of the invention and therefore the content is decrypted by the NAPO node. This is why, in a step 405, the NAPO node 101 stops the decryption of the stream, in order to make the connection with the source terminal STB 100 private, within the meaning of the invention. At a step 406, the NAPO node obtains the parameters Kx and Nc which serve to define the encryption key used by the source terminal STB 100 for the secure transmission of the audio-video content on the link 107. If at step 402, it is determined that the stream is not already in progress, the NAPO source node 5 initiates a DTCP exchange with the set-top box STB 100, including an authentication phase in a step referenced 403 and a key exchange phase and encryption / decryption in a step referenced 404 (see the description above of Figure 2). During this exchange, the set-top box STB securely transmits the parameters Nc and Kx to the source node NAPO. From these 10 parameters, the source node NAPO can calculate the first encryption key Kc with which the set-top box STB 100 has encrypted the encrypted content that it transmits to the source node NAPO. In a step referenced 407, the source node NAPO generates a password from the parameters Nc and Kx, determines, in a step referenced 408, a third entity of the network 1000 to which this password must be supplied and provides, in a step referenced 409, this password to said third party entity. In the example discussed here, this third entity is the controller, as described later in connection with FIG. 6. Several scrambling methods, well known to those skilled in the art, can be used for generation of the password from the Nc and Kx parameters, and in particular an Advanced Encryption Standard (AES) type mechanism which is a symmetric coding block capable of encrypting and decrypting information. The AES algorithm can use 128, 192 and 256 bit cryptographic keys to encrypt and decrypt 128-bit block data. The parameters Kx and Nc can be used as input to the AES algorithm and the result 25 will be the password provided to the user. Other methods, well known to those skilled in the art, can be used for the generation of the password. Any bijective function or a combination of bijective functions can be used, the purpose being to be able to deterministically obtain the password from the parameters Nc and Kx, and to be able to obtain, using the inverse function or the combination of functions. inverses (it (s) -even bijective (s)), the parameters Nc and Kx from the password.

According to another embodiment of the invention (not represented on the flowchart), the source node NAPO directly supplies the parameters Nc and Kx to the third entity (for example the controller). The third party entity is then responsible for providing these parameters only to the destination nodes connected to destination devices 5 authorized to receive the private content in the clear. For example, the third-party entity may provide key settings to unconditional destination nodes when the connection for transporting the content is first established, and subject to a password when additional connections are requested to serve the destination. new destination devices. In this case, the third party maintains a look-up table for each content it supports, including an identifier of the content, the key parameters Nc and Kx associated with it and a password to condition the delivery of these key parameters. In this other embodiment, it is not necessary to have a bijective function between the password and the key parameters Nc and Kx.

In steps referenced 410 and 411, the NAPO source node 101 initiates a DTCP exchange with the destination node NAP1 102, in order to exchange a second encryption key Kc1, in order to secure the transmission between NAPO 101 and NAP1 102. steps are obviously not necessary if the source node NAPO and the destination node NAP1 have already established a secure connection for the transfer of this content, as may be the case when, for example, it was determined at the stage 402 that the connection was already established but considered not to be private within the meaning of the invention. In a step referenced 412, after all the stream connections have been established (on the one hand between the set-top box STB and the source node NAPO, and on the other hand between the source node NAPO and the destination node NAP1), the source node NAPO: - receives the encrypted content with the first key Kc and from the set-top box STB 100; - does not decrypt the encrypted content with the first key; encrypts with the second key the content already encrypted with the first key, thus obtaining a doubly encrypted content; then during a step referenced 413: 2907287 23 - transmits the doubly encrypted content to the destination node NAP1. Thus, the NAP1 destination node 102 can then decrypt the doubly encrypted content with the second key, obtaining the encrypted content once with the first key Kc, and then transmit the encrypted content only once to the HDD digital hard drive so that he stores it. The content is stored in an encrypted form with the first key Kc. It should be noted that, for example, if the hard disk HDD 103 is connected to the node NAP1 by means of a link 108 of the IEEE1394 type, the destination node NAP1 102 initiates a DTCP exchange with the hard disk HDD 103, in order to exchange a third encryption key Kc2, in order to secure the transmission between the destination node NAP1 102 and the hard disk HDD 103. The destination node NAP1 102 encrypts with the third key the content already encrypted with the first key, thus obtaining a content, once again, doubly encrypted. Thus, the hard disk HDD 103 can then decrypt with the third key the double encrypted content, obtaining the encrypted content only once with the first key Kc in order to store it. The content is here also stored in encrypted form with the first key Kc. This implementation appears in the steps 511 to 517 of FIG. 5. In relation to the flowchart of FIG. 5, a particular embodiment of a method according to the invention for the secure transmission of a content, from the backbone network to a destination terminal, in the context of Figure 1. It is recalled that in the illustrative example considered, it is assumed that the user wants the content stored by the HDD digital hard drive 103 is securely transmitted to the digital television DTV 105, via nodes NAP1 102 (storage node) and NAP2 104 (destination node).

In a step referenced 501, the destination node NAP2 104 receives a request from a controller requesting the reading and transmission to the digital TV DTV 105 of previously stored content. After receiving this request, the destination node NAP2 104 detects in a step 502 whether the requested content is private content, for example by consulting a table summarizing all the private content currently stored. This table can be stored on one of the nodes (NAP2 104 for example) or on each node of the backbone. In the event of positive detection, the destination node NAP2 104 knows that it must implement the method according to the invention, ensuring a secure transmission end-to-end of this content (not only between nodes, but also up to reception by the digital TV DTV 105). If the requested content is not private content, the NAP2 node 104 must proceed with the secure transfer (with fourth and fifth keys Kc3 and Kc4, respectively) of the data it receives from the NAP1 node and forward to the destination terminal, according to the usual method, as presented in steps 511 to 517 (already described above in the case where the node NAP1 receives the node NAPO and transmits to the destination terminal HDD, with third and second keys Kc2 and 10 Kcl respectively). If the requested content is private content, in a step referenced 503, the destination node NAP2 104 obtains a password corresponding to the content to be transferred for viewing. This password is transmitted by the controller during step 610, which will be described later in connection with FIG.

In a step referenced 504, the destination node NAP2 104 obtains the parameters Nc and Kx of the first key Kc, from the password supplied by the user to the controller (step 608 of FIG. 6) and then by the controller at destination node (step 610 of FIG. 6) (if this password is the correct one). For this, the destination node NAP2 104 uses a method of descrambling (in English descrambling) in reverse that used in step referenced 407 in Figure 4). In a step referenced 505, the destination node NAP2 104 uses the parameters Nc and Kx of the first key Kc during a DTCP exchange with the digital television DTV 105. More specifically, the destination node NAP2 104 does not generate new values. for the DTCP parameters (random number and exchange key) but 25 during the key exchange phase with the DTV digital television 105 uses the parameters Nc and Kx obtained in the previous step referenced 504. Thus, the digital TV DTV 105 can calculate the first key Kc. In steps referenced 506 and 507, the destination node NAP2 initiates a DTCP exchange with the source node NAP1 102 to exchange a sixth encryption key Kc5.

In a step referenced 508, after all the stream connections have been established (on the one hand between the source node NAP1 102 and the destination node NAP2 104, and on the other hand between the destination node NAP2 104 and the television set digital DTV 105), the destination node NAP2 104 receives a doubly encrypted content (with the first and third keys, Kc and Kc5, respectively) from the source node NAP1 102. In the step referenced 509, the destination node NAP2 104 decrypts with the sixth key the content doubly encrypted with the first and sixth keys, thus obtaining an encrypted content only once, with the first key Kc.

In a step referenced 510, the destination node NAP2 104 does not encrypt the encrypted content with the first key (it is indeed already), and transmits the encrypted content with the first key to the digital television DTV 105. Thus, the DTV digital television 105 can then decrypt with the first key Kc the encrypted content it receives (see the step referenced 505 for obtaining the first key Kc by the digital television DTV 105), obtaining the unencrypted content. If the password provided by the controller in step 503 corresponds to the password constructed in step 407, the parameters Nc and Kx obtained in step 504 are those corresponding to the first key Kc and the content is therefore correctly displayed by the DTV 105 digital TV.

Note that if at the time the receiving node receives the request for a private stream connection, the content is already in transit to the destination terminal through the destination node, but not privately, the destination node will have to stop the encryption means of the stream in question, break the current connection, and then establish a new connection without reactivating the encryption means for this stream. Indeed, even if the content to be displayed is the same, the method of transport through the network changes, as indicated in step 402. The encryption key corresponding to the flow transported securely between the destination node and the destination terminal change: in the first case, this key Kc3 corresponds to the key parameters Nc3 and Kx3 exchanged between the destination node and the destination terminal, as indicated in steps 511 and 512. In the second case, this key Kc corresponds to the key parameters Nc and Kx exchanged between the source node 2907287 26 and the source terminal, as indicated in step 504. In addition, in the first case, the destination node must encrypt the stream to transmit it securely to the destination terminal; in the second case, the destination node must not encrypt the stream to transmit it securely to the destination terminal, because it is already encrypted with the key Kc. It should also be noted that the opposite approach is applied in the case where a connection changes from a private status to a non-private status, within the meaning of the invention. The destination node will have to break the current connection, then establish a new connection with new key parameters exchanged with the destination terminal and activate accordingly its encryption means for this stream. We now present, in connection with the flowchart of Figure 6, a particular embodiment of a method according to the invention of secure transmission of content, from a source terminal to a destination terminal, in the context of the figure 1.

In a step 601, the controller receives a user request for a private flow connection. The controller is preferably a node of the network 1000 which provides an interface to the user allowing him to put in communication source and recipient terminals, in order to view, record, ... audio-video contents. Each node or terminal element of the network 1000 may act as a controller. It will be considered preferentially in the remainder of the description that any NAPO node 101, NAP1 102, NAP2 104, NAP3 112 of the backbone network will act as a controller and will interface with the user. In step 602, the controller determines the source node, as well as the source terminal concerned by the request. In the example used so far, the source node is NAPO 101 and the source terminal is the set-top box STB 100, in the case of storing private content on the HDD hard disk 103; the source node is NAP1 102 and the source terminal is the hard disk HDD 103, in the case of the replay of a private content previously stored on the hard disk HDD 103. In step 603, the controller determines whether the source terminal is a storage device. In the case of a positive determination, the controller sends a simple stream connection request. Indeed, when one places oneself in the case where a private content 2907287 27 must be read from the hard disk HDD 103, the stored content is encrypted with the first key Kc, as already described in relation to FIG. processing of this stream is transparent to the destination node NAP1. It must therefore establish the transfer securely with the source terminal, that is to say the hard disk HDD 103 and decrypt said stream with the key determined during the DTCP exchange phase with the hard disk HDD 103. It must then encrypt this stream with another key determined during the DTCP exchange phase with the destination node NAP2 104. This is the usual procedure that is used here for the destination node NAP1 102 to transfer the flow to NAP2 recipient node 104.

In a step 605, the controller determines the destination node, as well as the destination terminal concerned by the request. In the example used so far, the destination node is NAP2 104 and the destination terminal is the digital television DTV 105, in the case of replaying private content previously stored on the hard disk HDD 103.

In step 606, the controller determines whether the destination terminal is a storage device. If so, the user request is to make a disk-to-disk copy of the content. The controller therefore sends a simple stream connection request to the destination node. The encrypted content with the first key Kc is then transferred from one disc to another using the usual manner. The content will thus always be encrypted with the first key Kc, even though it has been moved. If, in step 606, the controller determines that the destination terminal is not a storage device, the user request is to view the private content previously stored. The controller then obtains at step 608 a password that must correspond to the content to be displayed. This can be done, for example, by requesting, via its man-machine interface, the user to provide the password that was previously communicated to him (see step referenced 616 in FIG. the recording of the audio-video stream on the hard disk HDD 103. The controller then indicates to the destination node, in step 609, that the connection is private and that it must implement the invention as described in relation 5, it then sends, during a step referenced 610, the password obtained in step 608 to the destination node, which will use it to determine the parameters Kx and 2907287 28 Nc that it can provide the destination terminal DTV 105 to rebuild the key Kc and thus decrypt the private content. The content is thus correctly displayed by the digital television DTV 105. Thus, if another user tries to access private content previously stored by the first user on the HDD 103 according to the method described above, the destination node NAP3 112 receives, via its man-machine interface (for example a graphic interface associated with a remote control unit), a request to read and transmit to the digital television DTV 110 previously stored content. This second user does not have the password 10 determined in step 407, that is to say when the first user asked to store the content privately, the correct parameters Nc and Kx can not be obtained, so the first key Kc can not be determined and therefore the content can not be correctly displayed by the digital television DTV 110. If, in step 603, the controller determines that the source terminal is not a In the storage device, the controller sends, in step 611, a private stream connection request. Indeed, when one places oneself in the case where private content is to be stored on the hard disk HDD 103, the content must be stored encrypted with the first key Kc, as already described in connection with FIG. NAPO source node 101 must therefore implement the invention by not decrypting the transferred content of the STB set-top box 100. In a step 612, the controller determines the destination node and the destination terminal concerned by the request. In the example used so far, the destination node is NAP1 102 and the destination terminal is the hard disk HDD 103, in the case of storage of private content on the hard disk HDD 103.

At step referenced 613, the controller determines whether the destination terminal is a storage device. If this is the case, the user request is to make a private copy of a content, as is the case in the example presented so far where the content from the set-top box STB 100 must be stored on the HDD 103. Then, in step 618, the controller sends the destination node a request for a single stream connection. Indeed, when one places oneself in the case where private content is to be stored, on the hard disk HDD 103, the content must be stored encrypted with the first key Kc, as already described in connection with FIG. 4. The processing of this stream is transparent for the destination node NAP1. It must therefore establish the transfer securely with the destination terminal, that is to say the hard disk HDD 103 and encrypt said stream with the key determined during the DTCP exchange phase with HDD 103 HDD. It is therefore the usual procedure that is used here for the NAP1 destination node 102 to transfer the stream to the destination terminal HDD 103. At the step referenced 619, the controller receives the password associated with the private content, c ' that is, the password obtained from the parameters Nc and Kx which make it possible to define the first key Kc with which the content is encrypted by the source device. This password is sent by the source node to the step referenced 409, as described in connection with FIG. 4. The controller can then display the password to the user by means of its graphical interface. at a step referenced 620. This password will be reused when replaying the private content from the hard disk HDD 103, as already described and indicated at the step referenced 608.

The user having made the storage request therefore has a private information, which is said password, which enables him to view from a DTV digital television set 105, 110, the content thus stored. Any other user, having no knowledge of said password, will be unable to view private content stored according to the invention.

In order to explain the steps referenced 614 to 617 of the flowchart of FIG. 6, a particular embodiment of a method according to the invention for the secure transmission of a content in the case of a transmission is now presented. without intermediate storage, in the context of Figure 1. In the illustrative example considered, it is assumed that the user wants a content received by the STB box 100 (source terminal) is transmitted securely via the nodes NAPO 101 (source node) and NAP2 104 (destination node), up to DTV TV 105 (destination terminal). During a step referenced 601, the controller receives a user request for a private flow connection. At the step referenced 602, the controller determines the source node, as well as the source terminal concerned by the request. In the example used hitherto, the source node is NAPO 101 and the source terminal is the STB 100 decoder box. At the step referenced 603, in the example under consideration, the controller determines that the private content n ' is not located on a storage device. It then sends, at the step referenced 611, to the source node NAPO 101 a private flow connection request, so that the source node NAPO 101 implements the invention, as shown in FIG. step referenced 612, the controller determines the destination node, as well as the destination terminal concerned by the request. In the example under consideration, the destination node is NAP2 104 and the destination terminal is the DTV 105 television. At the step referenced 613, in the example under consideration, the controller determines that the destination terminal is not a communication device. storage. It then sends, at the step referenced 614, to the destination node NAP2 104 a private flow connection request, so that the source node NAP2 104 implements the invention, as shown in FIG. 5. At the referenced step 615, the controller receives the password associated with the private content, i.e. the password obtained from the parameters Nc and Kx which make it possible to define the first key Kc with which the content is encrypted by the user. source device. This password is sent by the source node NAPO 101 to the step referenced 409, as described in connection with FIG. 4. The controller can then display the password to the user by means of his graphical interface, during a step referenced 616. This password can be reused by the user, if he wants to move to another access point of the network, for example to view the private content on DTV 110. This case will be more fully described in connection with FIG. 7. The controller then sends, during a step referenced 617, the password received at the step referenced 615 to the destination node, which is will be used to determine the parameters Kx and Nc that it can provide to the destination terminal DTV 105 to reconstruct the key Kc and thus decrypt the private content. The content is thus correctly displayed by the digital television DTV 105. It thus appears that in the case where the private content is viewed without intermediate storage, the user does not need to enter the password in the procedure. The password is sent directly from the controller to the destination node. The user is simply informed of this password in the event that the user decides to record, for example on the hard disk HDD 103, the private content being viewed. Indeed, the source node NAPO 101 already implementing the invention in the context of viewing the content on the TV DTV 105, it will simply be necessary to establish a flow connection in the usual manner with the hard disk HDD 103 to store said content privately, within the meaning of the invention. Using the same password used for viewing on the DTV 105 television, the user will then be able to replay the private content stored on the hard disk HDD 103. It is now presented, in connection with the FIG. 7 is a flow diagram of a particular embodiment of a method according to the invention for the secure transmission of a content, from a source terminal to a destination terminal, in the context of FIG. 1, said content being already in In fact, up to now it has been considered, for the sake of simplification of the description of the invention, that the private connection request concerned a stored private content or a non-private content for the private network. which the user requested a private treatment, within the meaning of the invention. However, as already mentioned, the user may want to store on a disc private content already being viewed or may want to move to another access point of the network to view this content. At the step referenced 701, the controller receives a user request for a private stream connection, in the same manner as previously described. At the step referenced 702, the controller determines whether the flow connection considered is relative to a private content, within the meaning of the invention, already being transmitted within the network 1000. If this is not the case, the flowchart returns to step referenced 601 and the process executes as previously described.

If at the step referenced 702, it is determined that the considered stream connection is relative to a private content already being transmitted within the network 1000, in a step 704, the controller determines the destination node, and the destination terminal concerned by the request. In the event that a user wishes to access the private content from the set-top box STB 100 from the television DTV 110, said content being already displayed on the television DTV 105, the destination node is NAP3 112 and the destination terminal is the television DTV 110. In the case where a user wishes to store private content from the set-top box STB 100 on the hard disk HDD 103, said content already being displayed on the television DTV 105, the destination node is NAP1 102 and the destination terminal is the hard disk HDD 103. At the step referenced 705, the controller determines whether the destination terminal is a storage device. If so, the user request is to make a private copy of a content. As already described above, in step 706, the controller sends the destination node a request for a single stream connection. A connection will then be established from the source terminal STB 100 to the destination terminal HDD 103 and the content will be stored encrypted with the first key Kc, used by the source 10 for the transfer of the content securely on the link 107. step 705, the controller determines that the destination terminal is not a storage device, the controller then obtains, at the step referenced 707, a password to match the content to be viewed. This can be done, for example, by requesting, through its man-machine interface, the user to provide the password that has been previously communicated (see the steps referenced 616 and 620 in Figure 6). The controller then indicates to the destination node, at the step referenced 708, that the connection is private and that it must implement the invention as described in relation to FIG. 5. It then sends, during a step referenced 709, the password obtained at the step referenced 707 to the destination node, which will use it to determine the parameters Kx and Nc that it can provide to the destination terminal DTV 110 to reconstruct the key Kc and thus decrypt the private content. The content is thus correctly displayed by the digital television DTV 110. As already stated, the controller can be any node of the network 1000. In the case where the controller is confused with the source node or the destination node, the 25 steps of sending or transmitting data from the controller to the source node or the destination node refer to internal information exchange mechanisms that do not require further description, being well known to those skilled in the art. Also, the present invention can be implemented using any content protection protocol directly having a key exchange phase and not key parameters.

Claims (5)

  A method for securely transmitting private content between a source device (STB) and at least one destination device (DTV) through a source node (NAPO) to which the source device (STB) is connected and at least one destination node (NAP2) to which said at least one destination device (DTV) is connected, said source device and source node using a content protection protocol having a key parameter exchange phase (Nc, Kx) and a content transmission phase encrypted with the key associated with the key parameters exchanged, characterized in that the method comprises the following steps: - reception by the source node (NAPO) parameters (Kx, Nc) associated with a first key during said exchange phase of key parameters between the source device and the source node (404); - receiving by the source node (NAPO) encrypted content with said first key during said transmission phase between the source device and the source node; transmission by the source node (NAPO) of the content encrypted at least with the first key to audit at least one destination node (413); and associating a password with the private content (407), for conditioning the access by said at least one destination node to the key parameters associated with the first key.   2. Method according to claim 1, characterized in that the step of associating a password to the private content is performed by a controller node in charge of establishing a connection between the source device and the destination device for the transmission of the private content, said step of associating a password with the private content comprising the following steps: receiving the parameters (Kx, Nc) associated with the first key and transmitted by the source node (NAPO); - exchange, through a user interface of the controller node, the password with a user, the password being defined by the controller node or the user; 2907287 34 - Storage of the password in an association table comprising an identifier of said content, said password and the key parameters associated with the first key.   3. Method according to claim 2, characterized in that the password is defined by the controller and in that said password is obtained using the key parameters associated with the first key.   4. Method according to claim 1, characterized in that the step of associating a password to the private content is performed by the source node (NAPO) and comprises the following steps: - generation of the password in using the key parameters associated with the first key; and providing the password to a user, through a user interface of the source node (NAPO).   5. Method according to claim 1, characterized in that the step of associating a password to the private content is performed by the source node (NAPO) and comprises the following steps: - generation of the password in using the key parameters associated with the first key; and providing the password to a controller node in charge of establishing a connection between the source device and the destination device for the transmission of the private content, and in that the method further comprises the following step, performed by the controller node: - providing, through a user interface of the controller node, the password 25 to a user. 8. Method according to one of claims 1 to 5, characterized in that said password is the result of a bijective function applied to the key parameters associated with the first key. 9. Method according to claim 1, characterized in that the step of associating a password to the private content is performed by the source node (NAPO) and comprises the following steps: 2907287 generation of the password using the key parameters associated with the first key; supplying the password to a controller node in charge of establishing a connection between the source device and the destination device for the transmission of the private content, and in that the method further comprises the following steps performed by the controller node : - exchange, through a user interface of the controller node, a second password with a user, said second password being defined by the controller node or the user; storing said second password in an association table comprising an identifier of said content, said password and said second password. 8. Method according to one of claims 1 to 7, characterized in that it further comprises the following steps: 15 - encryption with a second key, by the source node, encrypted content with the first key, in order to obtain double encrypted content; transmission by the source node of parameters associated with the second key, during a phase of exchange of key parameters between the source node and the said at least one destination node; and 20 -transmission of the doubly encrypted content, during the step of transmission by the source node of the encrypted content at least with the first key. 9. A method of securely receiving private content by at least one destination device (DTV) through at least one destination node (NAP2) to which said at least one destination device (DTV) is connected, said destination device and destination node using a content protection protocol having a key parameter exchange phase (Nc, Kx) and an encrypted content transmission phase with the key associated with the key parameters exchanged, characterized in that the method comprises the following steps: - receiving by said at least one destination node (NAP2) private content, previously encrypted with a first key and from a source device (STB, HI) D) through a source node (NAPO, NAP1) ) to which said source device is connected (508); obtaining a password associated with the private content (503); determining the key parameters (Kx, Nc) associated with said first key, by using the password obtained in the obtaining step (504); transmitting by said at least one destination node (NAP2) said key parameters to the destination device during said key parameter exchange phase between the destination node and the destination device (505); and - transmitting the encrypted content with the first key received at the receiving step 10 to the destination device (510). 10. Method according to claim 9, characterized in that the step of obtaining a password and the step of determining the key parameters (Kx, Nc) associated with said first key are performed by said at least one key. a destination node (NAP2), and in that the step of obtaining a password is performed by the input of said password by a user, through a user interface of said at least one destination node (NAP2). ). 11. Method according to claim 9, characterized in that the step of obtaining a password and the step of determining the key parameters (Kx, Nc) associated with said first key are performed by a controller node. in charge of establishing a connection 20 between the source device and the destination device for the reception of the private content, in that the step of obtaining a password is performed by the entry of said password by a user , through a user interface of said controller node, in that the step of determining the key parameters (Kx, Nc) is performed by reading, from the password obtained at the obtaining step, an association table 25 comprising an identifier of said content, said password and the key parameters associated with the first key, and in that the method further comprises a step of transmitting to said at least one destination node (NAP2), by the control node r, parameters (Kx, Nc) determined in the determination step. The method of claim 9, characterized in that the step of obtaining a password is performed by a controller node in charge of establishing a connection between the source device and the destination device for the purpose of obtaining a password. receiving the private content, said step of obtaining a password being effected by the entry of said password by a user, through a user interface of said controller node, in that the method further comprises a transmission step auditing at least one destination node (NAP2), by the controller node, of the password obtained in the obtaining step, and in that the step of determining the key parameters (Kx, Nc) is performed by said at least one destination node (NAP2) from the password transmitted by the controller node. 13. Method according to one of claims 9 to 12, characterized in that the password obtained in the obtaining step is the result of a bijective function applied to the key parameters associated with the first key and the step of determining the key parameters associated with the first key is performed by applying the inverse function of the bijective function to said password. The method of claim 9, characterized in that the step of obtaining a password is performed by a controller node in charge of establishing a connection between the source device and the destination device for receiving the password. private content, said step of obtaining a password comprising the following steps: obtaining a second password by entering said second password by a user, through a user interface of said controller node; determination of said password by reading, from said second password, an association table comprising an identifier of said content, said password and said second password; in that the method further comprises a step of transmitting to said at least one destination node (NAP2), by the controller node, the password obtained at the step of determining said password, and that the step of determining the key parameters (Kx, Nc) is performed by said at least one destination node (NAP2) from the password transmitted by the controller node. The method according to one of claims 9 to 14, characterized in that the content received by the destination node is doubly encrypted with the first key and a second key and in that the method further comprises the following steps: a step of authentication and exchange of key parameters associated with the second key between the source node and the destination node; and decrypting, with the second key, the doubly encrypted content, in order to obtain the encrypted content only with the first key. 16. Computer program product downloadable from a communication network e: t / or recorded on a computer readable medium and / or executable by a processor, characterized in that it comprises program code instructions for the performing the steps of the secure transmission method according to at least one of claims 1 to 8 and / or the secure receiving method according to at least one of claims 9 to 15, when said program is executed on a computer. 17. Storage medium, possibly completely or partially removable, readable by a computer, storing a set of instructions executable by said computer to implement the secure transmission method according to at least one of claims 1 to 8 and / or the secure receiving method according to at least one of claims 9 to 15. 18. Source node (NAPO) capable of participating in the secure transmission of private content between a source device (STB) and at least one destination device (DTV) to through said source node (NAPO) to which the source device (STB) is connected and at least one destination node (NAP2) to which said at least one destination device (DTV) is connected, said source device and source node using a content protection protocol having a key parameter exchange phase (Nc, Kx) and an encrypted content transmission phase with the key associated with the key parameters exchanged, characterized in that the source node comprises: - parameter receiving means (Kx, Nc) associated with a first key during said key parameter exchange phase between the source device and the source node; Means for receiving the encrypted content with said first key during said transmission phase between the source device and the source node; - means for transmitting the encrypted content at least with the first key audit at least one destination node, a password being associated with the private content, for conditioning access by said at least one destination node to the key parameters associated with the first key. 19. Source node (NAPO) according to claim 18, characterized in that it comprises means for transmitting the parameters (Kx, Nc) associated with the first key to a controller node in charge of establishing a connection between the device. source and the destination device for the transmission of the private content, so that said controller node performs the association of a password to the private content. 20. Source node (NAPO) according to claim 18, characterized in that, to perform the association of a password to the private content, it comprises: - means of generating the password using the parameters of key associated with the first key; and - means for providing the password to a user, through a user interface of the source node (NAPO). 21. Source node (NAPO) according to claim 18, characterized in that, to perform the association of a password to the private content, it comprises: - means for generating the password using the key parameters associated with the first key; and means for providing the password to a controller node in charge of establishing a connection between the source device and the destination device for the transmission of the private content, so that the controller node provides, through a user interface of the controller node, the password to a user. 22. Source node (NAPO) according to one of claims 18 to 21, characterized in that said password is the result of a bijective function applied to the key parameters associated with the first key. 23. Source node (NAPO) according to claim 18, characterized in that, to perform the association of a password to the private content, it comprises: - means for generating the password using the key parameters 30 associated with the first key; 2907287 - means for providing the password to a controller node in charge of establishing a connection between the source device and the destination device for the transmission of the private content, so that the controller node: * exchanges, through a user interface the controller node, a second password with a user, said second password being defined by the controller node or the user; stores said second password in an association table comprising an identifier of said content, said password and said second password. 24. Source node (NAPO) according to one of claims 18 to 23, characterized in that it comprises: - encryption means with a second key encrypted content with the first key, to obtain a doubled content encrypted; means for transmitting parameters associated with the second key during a key parameter exchange phase between the source node and the said at least one destination node; and in that said transmitting means encrypted content at least with the first key transmit said doubly encrypted content. 25. Destination node (NAP2) capable of participating in the secure reception of a private content by at least one destination device (DTV) through at least said destination node (NAP2) to which said at least destination device (DTV) is connected, said destination device and destination node using a content protection protocol having a key parameter exchange phase (Nc, Kx) and an encrypted content transmission phase with the key associated with the exchanged key parameters, characterized in that it comprises: - means for receiving the private content, previously encrypted with a first key and from a source device (STB, HDD) through a source node (NAPO, NAP1) to which said source device is connected; means for receiving or determining the key parameters (Kx, Nc) associated with said first key, said key parameters being determined by the use of a password associated with the private content and previously obtained; Means for transmitting said key parameters to the destination device during said phase of exchange of key parameters between the destination node and the destination device; and means for transmitting to the destination device the encrypted content with the first key received by the reception means. 26. Destination node (NAP2) according to claim 25, characterized in that it comprises: means for obtaining said password, by the input of said password by a user, through a user interface of said at least one user interface. a destination node (NAP2); and - means for determining the key parameters (Kx, Nc) associated with said first key, from the password obtained. 27. Destination node (NAP2) according to claim 25, characterized in that it comprises means for receiving the key parameters (Kx, Nc) associated with said first key, said key parameters being determined and transmitted by a node. controller responsible for establishing a connection between the source device and the destination device for receiving the private content. 28. Destination node (NAP2) according to claim 25, characterized in that it comprises: means for receiving said password obtained by a controller node in charge of establishing a connection between the source device and the destination device for the reception of private content; and - means for determining the key parameters (Kx, Nc) associated with said first key, from the password received. 29. Destination node (NAP2) according to one of claims 25 to 28, characterized in that the password obtained is the result of a bijective function applied to the key parameters associated with the first key, and in that the means for determining the key parameters associated with the first key apply the inverse function of the bijective function to said password. The destination node (NAP2) according to one of claims 25 to 29, characterized in that the content received by the destination node is doubly encrypted with the first key and a second key and in that the node destination comprises: - means for authentication and exchange of key parameters associated with the second key, between the source node and the destination node; and decrypting means, with the second key, of the doubly encrypted content, in order to obtain the encrypted content only with the first key.