Secure and personalised distribution of audiovisual flows by means of a hybrid unicast/multicast system

RELEASE SECURE AND CUSTOM VISUAL FLOW BY A HYBRID UNICAST / MULTICAST

The present invention relates to the field of distribution of digital audiovisual sequences. It is proposed in the present invention to provide a method and a system to protect visually and / or audibly an audiovisual sequence from a digital standard, digital standard or standard owner to distribute it securely in "multicast" through a telecommunications network and restore its original content on a recomposition module of the target equipment from a protected digital audiovisual stream mode. The present invention relates more particularly to a device capable of securely transmitting through a telecommunications network a set of high quality audiovisual streams to a display screen and / or to an audio output belonging to a terminal or device display, such as a television screen, a computer or a mobile terminal type phone or PDA (Personal Digital Assistant), or another while preserving the audiovisual quality but avoiding any fraudulent use such as the possibility of making pirated copies broadcast content. The invention basically refers to a method and a client-server system that protects audiovisual content separated into two parts, the second part being absolutely essential for the reconstitution of the original stream, the latter being restored according to the recombinant the first portion with the second portion the method used for the description of a preferred embodiment in the present invention separates the audiovisual stream into two parts, so that the Part called "modified main stream" contains almost all of the initial information, for example over 99%, and a second section called "Additional information" containing targeted elements of the initial information, which is very small size relative to the first part. The additional information contains data extracted from the original stream, said extracted data being replaced by "decoys" in the modified main stream, so as to cause a strong audiovisual degradation, while retaining said protected main stream compliant or standard of the original stream. Currently, it is possible to transmit audiovisual streams in digital form via the kind of radio broadcast networks, cable, satellite, etc. or via telecommunications such as DSL network (Digital Subscriber Line) or BLR (local loop) or via DAB (Digital Audio Broadcasting), and via any wireless telecommunication network GSM (Global System for Mobile) GPRS (General Packet Radio Service), UMTS (Universal Mobile Telecommunication System), Bluetooth, WiFi, etc. Moreover, to prevent piracy of audiovisual works and disseminated, the latter are frequently encrypted or scrambled by various means well known by one skilled in the art.

The prior art known to US 6295361 with a method and apparatus for a key management node to decide on the process of change in certain key nodes group within a multicast group using d an indicator inserted in a multicast packet. The node manager decides how to insert the indicator and what are the nodes involved. The new key is sent and when all nodes of the group received their keys, the manager node sends a flag, or a date from which all members of the group are allowed to use the new key. This prior art is a method of managing the multicast session with dynamically changing group of key, the same key is assigned to all members of the same group, with which data can be decrypted. However, protection is used encryption and data initially present in the audiovisual stream remain inside the protected stream. Therefore, this prior art does not address the high security and personalization problem, object of the present invention. The prior art also refers to WO 02/11356 A2 discloses a method for managing keys between the client and the server in a multicast environment. The method is based on establishing a secure channel between the server and the client using an SSL (Secure Socket Layer) or TLS (Transport Layer Security) with some modifications in the order message exchange to can generate a key management and send this key customer through said secure channel from this key, the client generates future session key with the server. Customers of the same multicast group use the same management key to generate a session key for the communication session. This prior art does not meet the criteria secure transport of AV data, object of the present invention, the data, even if encrypted, is fully present in the protected data stream.

Unlike the prior art, the present invention provides a system characterized by the broadcast multicast of the complementary information, a processing is performed in real time on segments representing independent entities standpoint treatment, said segments comprising data for the reconstruction of full audio visual information, said segments being secured and personalized for each user, and sent to recipients equipment real time via a low bandwidth network from a central server acting as gatekeeper for viewing content. In the present invention, the term means

"Multicast" mode of transmission from a transmitter to all receivers belonging to the same group of subscribers, unlike the term "unicast" which is a method of transmission from a transmitter to a single receiver . The protection applied with content distributed by multicast secure system object of the present invention is based on the principle of removal and replacement of certain information in the encoded original audiovisual signal by any method, including: substitution, modification, permutation or travel information. The solution is to extract and retain permanently in a secure server complementary information, containing part of the original audiovisual stream, this part is indispensable for reconstructing said audiovisual program, but being a very small volume relative to the total volume of audiovisual program recorded at the user's or received in real time by the user. The complementary information is transmitted in multicast mode via the secure network transmission at the time of viewing and / or hearing said audiovisual program. F it to be removed and substituted with decoys part of the original data of the AV stream Initial upon generation of the modified main stream does not permit restitution of the original stream from said modified main stream, which is fully compatible with the format of the original stream, and can be copied and read by a reader classic. The modified main stream, however, is completely inconsistent to view human audiovisual perception. The original digital stream is separated into two parts, the largest part of the audiovisual stream, said modified main stream will be transmitted via a classic broadcasting network, while the missing part, complementary information will be sent on demand via a narrowband telecommunications network or via a physical medium such as a memory card, disk, etc. However, the two networks can be combined, while keeping the two separate transmission paths. For reconstitution of the original stream, additional information is sent piece by piece for viewing and / or hearing of the audiovisual stream. The object of the present invention is the secure and personalized transmission after authentication of the user, the additional information in multicast mode, to avoid that it can be copied or fall in full possession of user or any malicious person. Distribution multicast is used in cases where a large number of users want to access the same content and the same time, which is for example the case of the live broadcast via satellite or cable or other network enabling achieve several subscribers simultaneously. The content stream is transmitted from a server to the client via a multicast channel. By a separate channel, the designated customized and additional information for each active customer (group member multicast) is broadcast from a secure server also multicast. The user who is interested in content, joins the multicast group, receives the additional information according to its rights allowing the reconstitution of the original stream and thus the viewing simultaneously with the receipt of the additional information. On the one hand, the profit distribution in multicast mode additional information is a centralized server can model its distribution to a very large number of consumers. On the other hand, the disadvantage of the multicast distribution is the same as complementary information is transmitted to all users in the group and therefore it is more difficult to individually control the various consumers. From security point of view and content protection, multicast present models disadvantages "a several-toward-" or "only one transmitter, several receivers" of the English expression "one-to-many", which means a transaction communication from a single transmitter and s' Speaking to multiple receivers. Hence the need for a reliable protection system for multicast distribution and based on the following characteristics: • The solution of the present invention is complementary to the distribution protocol multicast "join / leave the group" well known man 1 art; • The decision to join / leave the group is performed at the network access elements for access control from a list previously drawn, the customer receives permission to join this group, but without have the right to this step, view the broadcast stream for the group, said elements of access being called switches; • Users with a switch denied leave can not join the group; "The central server is responsible for updating the list of customers and the decision to include new identities on the list of encryption keys for the session after an initial authentication step with the client wanting to join the group; • Each session key is individual to each customer and has its own life, after which it is considered an invalid key, then it is destroyed by the server; • The scale of a multicast group is in the order of several thousand users per group; • The relationship is of the one-to-all in one direction, so the server is still the source of emission and customers always receptors, with the exception of requests sent from the receivers to the server through a link back in unicast or, for example during the stage of authentication.

The feature of the present invention is that the server distributes multicast to a large number of users can join and leave the group dynamically. Moreover, in the present invention, one removes the selective relation feature ( "push relationship" in English), that is to say, customers of the same group can not communicate and therefore the model multicast connection is simplified, as the protocol of management and key distribution for the group. The object of the present invention is a simplified protocol for the secure delivery of the complementary information in multicast, thus completing _≠ multicast protocols existing broadcasting with a secure protocol broadcast complementary information. To this end, the invention pertains in its most general sense, a method for the secure distribution of digital audiovisual streams in a standard format, standardized or proprietary, said flows on which we shall, before transmission to the receiving equipment, a flow separation into two parts to generate a modified main stream with the format of the original stream, and complementary information of any format comprising digital information suitable for permitting reconstruction of the original stream, wherein the by separate channels are transmitted during the distribution phase modified main stream from a distribution server that the multicast mode is transmitted complementary information to said destination equipment from a secure central server via at least a router and at least one switch connecting said receiver equipment to said central server via at least one access point. Preferably, the authentication between the client and the server by unicast mode. In one embodiment of particular implementation, a unique session key for content and customer is generated by the central server following said authentication. Advantageously, the additional information is compressed and encrypted before sending to the client. Alternatively, the management of a multicast group is performed in the link layer controlling the distribution of multicast data only to the access point concerned. Preferably, the management and security of the complementary information is made following a multi-function authentication requests through a central server, and includes a compression step, an encryption step and a step of managing said keys session. According to a preferred embodiment, the regeneration of a new session key for the client is performed according to the client's decision to extend the connection is based on the life of the previous session key, and individual for each member of the multicast group. In another embodiment, additional information is secure and personalized for each customer and for each multicast session using hybrid or symmetric or asymmetric encryption methods. The invention also provides a system for secure distribution of audiovisual streams characterized in that the flow control in the multicast group is performed following the management and personalization of secure additional information. Preferably, the system according to the invention comprises a device for separating the original video stream in a modified main stream and complementary information, at least one multimedia server containing the protected audiovisual stream, at least one secure central server comprising means for security and customization of the complementary information from which is distributed additional information, at least one telecommunications network, at least one router, at least one switch serving as an access point to connect with the target equipment and a device on the destination device for the reconstruction of the original audiovisual stream based said modified main stream and the complementary information. The invention will be better understood with the aid of exemplary embodiments and the following detailed steps. A preferred embodiment, but not limited to the method that meets the criteria of safety and reliability is illustrated by the client system - server shown in FIG. The audiovisual stream digital form (1), transmitted via the link (6) to the analysis module and scrambling (2) is separated into two parts by this module (2). The modified main stream (17) is stored in a media server (16) and is sent in real time to the customer for viewing via a broadband network or is stored in advance on the terminal storage device (14) of 'user. The complementary information (3) is sent to the storage and segmentation module (41) of the secure central server (4). The additional information is sent only on request, its distribution in real time, its security and customization for each user is achieved through the property of "scalability in throughput" on transport networks. We define the notion of "scalability in throughput" as the ability of a network to manage, modify, distribute and adapt the speed of flow that pass depending on the available bandwidth or negotiated depending on congestion of network. Due to the low flow rate of the additional information transmitted in real time, the method of the present invention contains an additional information segmentation step in the module (41) that generates variable-sized data segments, each segment corresponding to a whole coherent audiovisual element subjectively, such as a picture or frame, a group of pictures or GOP ( "group of Pictures "in English) in an MPEG-2 stream, for example. Alternatively, the segmentation is performed in a single step after generating said complementary information (3) and produces a plurality of segments referred to as "flow supplementary information" which remain stored in the storage and segmentation module (41) . In another variant, the additional information stream is generated in real time. The complementary information segmentation step is followed by an encapsulation step in data blocks and an encryption step in the module (42), preceded by a compression step of size, where the blocks are still available to the demand from users. The flow of additional information is sent to the terminal (14) of the user continuously in the form of blocks, a block containing a segment to which were added access information or "header" with data relating to the identity of the user, in the case of a conventional centralized network. Preferably, the header contains data relating to the mobility of the user (position, free, network access points, for example) in the case of a distributed network. Advantageously, the header contains data relating to the encryption keys of the additional information stream. A block is the basic unit of communication, it is also called UFIC (Unit Flow Supplementary Information). When the "i" user wishes to view a sequence, it connects via its equipment (14i) and the link (13i) at its closest access point, switch

(12a), which gave him prior authorization to join the multicast group. The switch (12a) redirects the request via the link (IIa) to a local router (10a), the latter in turn address the application via the link (9a) to a central router (8), said central router (8) addresses the central server (4) via the link (7). When the server (4) and receives the client request (14i), the central server (4) requires authentication from the client (14i) to decide sending solicited UFIC, which are unique title audiovisual sequence. After the authentication dialog, customer identification (14i) by the central server (4) as contained in its database (5) and generating a unique session key, the flow in the segmented module ( 41) is sent over the link (43) to the module (42), compressed and encrypted in the module (42) said unique session key title and client.

The UFIC are then transported via the connection (7), the central router (8), the link (9a), the local router (10a), the link (IIa), the switch (12a) and the link (13i) to the terminal (14i) of the user (i). Advantageously, the terminal (14i) of the user has a smart card (15i), on which performs the decryption of the units of the flow of additional information. The switch (12a) is the head of security, it controls the addresses of clients in the access list consists of information on previous sessions with the client (eg, time and connection duration, prepayment or delayed, kind of visualized content), it ensures the personalization of each customer session so the additional information forming UFIC units. An implementation method is to use a hybrid method, such as using unicast for authentication using secure keys and multicast to broadcast one supplementary information. First, if the client (14i) managed to reach the desired multicast group via the switch (12a) is that it has recognized identity and authorization from the network for receiving said additional information packets after the authentication step; However, until a valid session key was not generated by the central server, the client can not use the UFIC, said UFIC being disseminated and only encrypted with keys of others (14j, 14k, etc. ). Second, the customer dialogue with the additional information server (4) in a point-to-point unicast, the authentication phase is thus performed to ensure that the client has sufficient rights to receive UFIC and to generate the session key (through a secure method for exchanging information), viewing rights being stored in a rights management database (5). At the end of this stage, the server (4) automatically adds the new client key (14i) in the session key list for the requested multicast group. The server (4) starts to encrypt the current UFIC with the session key and sends the UFIC with what is called a label that is issued to the client during the authentication step. Said label contains information on a unique combination of encrypted UFIC and every customer. The client (14i) receives packets of groups as long as it has said valid tag and decrypts data portions with said session key, until the lifetime of the session key expires. After a period long enough to have the right to request a new key and if the customer wishes to continue to receive additional information from the same multicast group, begins a new stage of authentication. Advantageously, the server (4) encrypts corresponding UFIC to simulcast the same content with the session keys of all authorized clients 14i, 14j, 14k, ...., 14q and sends a certain number of times the same UFIC each encrypted with different keys corresponding to the number of connected clients. Preferably, prior to encryption with all session keys, is applied compression of the additional information stream units, reducing the amount of information to be transported and also increasing the security of encrypted UFIC thereafter, reducing the redundancy because a lot of cryptographic analysis exploiting the redundancy in order to break the protection. The efficiency of the compression algorithm is also one of the factors that manages the flow of multicast scalability based group the number of members per group. Each user decrypts UFIC received using its own session key. The term "transmission cycle server" step of sending a UFIC as compressed, encrypted with all key members of the group to the address and port number of the multicast group. One advantage of this technique is that it provides resistance to hacking due to the fact that we apply a multiple encryption of the same content with different keys for different end devices. The compression mechanism is applied to the server of the transmission cycle to prevent too high traffic for groups with a significant number of members (thousands of users). This model is able to use any compression algorithm without loss of LZ

(Lempel-Ziv), e.g. LZW (LZ variant Terry

Welch's) LZJH (Lempel-Ziv-Jeff Heath v.44 or by ITU-T). Periodic renewals session keys are made to ensure their cryptographic security. For example, a session key may be valid for a period of two hours, during which the key will decrypt a quantity of UFIC having a flow rate of ten Kbits / s, for example equal to 2²⁰ blocks of data each 64 bits long. An extension of the observation function messages of the multicast group ( "snooping" in English) IGMP (Internet Group Management Protocol) on the last point of distribution (12) is used in the link layer to the access management (allow or deny) for each client on flows which said customer or not with the rights and accordingly optimizes bandwidth for each customer's access point, such as a DSLAM (Digital Subscriber Line access Multiplixer) of DSL (Digital Subscriber Line) network. Said extension of the observation function and provides a multicast transmission mode extended and secure. During the complementary information distribution phase is thus transmitted in the extended mode of multicast transmission and secured to said destination equipment from a secure central server via at least one router and at least one switch connecting said destination device to said central server via at least an access point. The system keeps customizing UFIC for each client, while reducing the number of connections by unicast server, with the exception of times of authentication. The system also optimizes the flow rate so the amount of data to be transmitted depending on the variation of the number of clients per group. Thus, access management and customization of the details (UFIC) control the flow in the multicast group. The current version of IGMP allows switches (12) to detect IGMP message member clients, sending the respective response and control the distribution of multicast packets to the client port. In the present invention, this function is supplemented by a filtering on the first level of control with a list of addresses of the MAC link layer (Medium Access Control), said customers representing addresses allowed to connect to the multicast group. Furthermore, labeling with a label is added to each packet of compressed and encrypted data, which represents the customer's identity and also a second level of control and customization. This identity is used by the switch (12) for determining the physical port to which the packets are distributed by sending the particular customer, only the marked packets with its own label. Alternatively, the UFIC is encrypted using symmetric encryption algorithms and the encryption key is then encrypted with a recipient's public key. It is a mode of hybrid authentication. In another variant, the UFIC is encrypted using asymmetric encryption algorithms and it's a way of PKI authentication ( "Public Key Infrastructure" in English). The present invention will be illustrated with the aid of a second preferred embodiment, which includes a multicast protocol, a method of mutual authentication and a compression method for the server comprising multicast protocols used and their expansion for the distribution of the complementary information, object of the present invention. The multicast transmission system is based on a group management protocol (IGMP) that is responsible for controlling to join / leave multicast group. This protocol is executed between the client (14i, 14j, 14k) and its network access point closest respectively, the switch (12a). Control multicast routing protocol multicast routing traffic since the switches (12) to all routers (10) of the distribution network. A control processor located inside the switch (12) observes the IGMP messages sent by clients (14). The switches can manage and emulate IGMP messages also use this information to dynamically configure their own filters observation. This solution optimizes the management of bandwidth at the switch, avoiding the overload of LAN ( "Local Area Network" in English), especially in cases where the end user frequently switches from one multicast group to another , for example during a change of television channel routers (10) in multicast routing carrier and the switches (12) to which the layer 3 of the OSI model is able to manage data used for this example, contain a bandwidth control with a rate limiting functionality in IP multicast allows to impose an upper limit for the traffic carried from the server to the multicast groups. The definition of the limits of mechanism includes the definition of a multicast source filter and a receiver filter multicast group by receiving port. This control filter is based on the IP address also on MAC address (address of the network card "Medium Access Control"), for example using the mechanism MVR (Multicast VLAN Registration) and therefore to avoid attribution fraudulent ( "spoofing" in English) of the customer's IP network address, a supplementary protocol st applied unicast "Unicast Reverse Path Forwarding" (uRPF) between the client (14) and the switch (12).