FR2872987A1 - SECURED DEMULTIPLEXING DEVICE AND METHOD AND ASSOCIATED PRODUCTS - Google Patents

Abstract

The present invention relates to a device (1) and a method for securely demultiplexing at least one multiplexed stream (FTM) of programs, each comprising encrypted representation data (CRYP) and access control data (CTRL). The device comprises means for receiving (11) the stream, demultiplexing means (DMX) according to a selection of one or more programs by a user, extracting the control and representation data of the selected program, means setting (12) a decryption key (CLE) from the access control data, and decrypting means (13) of the representation data, by means of this key.It also comprises means for storing (14) at least the encrypted representation data of the selected program, in a transient storage space (20), in parallel with the setting of the decryption key, and the means (15) for injecting these data es representation, the storage space to the descrambling means when the decryption key is established.

Description

The present invention relates to a device and a method for

  secure demultiplexing, as well as corresponding products.

  A digital signal receiver-decoder conventionally comprises a module having tuner and demodulator functions, a demultiplexer, a decryption module, video and audio decoders, access control modules and card interface modules. secure access, making the decryption module operational, and a central processing unit (CPU). Data for audio and video decoders are typically transmitted in an MPEG2 encoded transport stream (for Moving Picture Experts Group), in multiplexed packet-by-packet form. Each of these packets carries video, audio, or intended for the proper operation and use of the digital receiver. The demultiplexer makes it possible to direct the packets towards a processing or another, starting from a packet identifier in the header of this packet.

  It is usual to encrypt the packets on transmission by means of an encryption key, in order to control access to a digital program. This key is transmitted (at least partially) in a confidential format to the access control module. Among the data circulating in the receiver, some are encrypted and others not, only the encrypted data passing through the decryption module. The decryption key is generally reconstructed in the digital receiver, by using a secure access card which, from specific access control data transmitted in the digital train, makes it possible to reconstitute this key completely. The key is then positioned in the decryption module associated with the demultiplexer and has an identified packet train.

  In practice, each packet of the digital train is identified by a packet descriptor and by decryption support information, which make it possible to perform a possible decryption according to authorizations 2872987 -2- available in the secure access card. A decryption key may be associated with one or more packet identifiers. The number of keys to use to decrypt a complete stream is variable and depends on the type of access control and its implementation at the broadcast level.

  According to the image compression standards commonly used in video decoders, variations are coded from one image to another, in order to substantially reduce the number of data to be transmitted. It is thus customary to send groups of images, denoted GOPs (for Group Of Pictures), each of which contains at least one self-sufficient image for its decoding, the other images of the group depending on the one the other.

  In particular, the MPEG2 standard provides sequences of images in which only the detection of an intra-type image (image I), unique in each GOP, makes it possible to begin the decompression of a sequence. In the Joint Video Team (JVT) standard, only the detection of an IDR (Instantaneous Decoder Refresh) image allows to start the decompression of a video sequence, which contains several type I images. The GOP is dimensioned by the IDR type image. The detection of this type of image is usually carried out either by the demultiplexer, or by one of the audio and video decoders, or by the CPU, by a search operation in memory.

  The size of the video sequences results from a compromise between an effective video compression concern (size as large as possible) and reasonable processing operations for the type of image to be encoded (tolerable limit for the size). Usually, the number of images per sequence is thus between 24 and 60, which results in a diffusion duration typically of the order of 500 ms to more than 1 s for an image group. Larger sequence encodings are nevertheless envisaged, with a duration of between 2 and 5 s.

  2872987 -3- This size of sequence has a direct impact on the duration of a program change (zapping), because the decoding can start only after the reception of a type I image for MPEG2 or IDR for J \ / T. The average time required to establish video decoding once the data is ready for use is in fact half the duration of a sequence, and is therefore usually between 240 and 500 ms.

  Another factor increasing the video decoding start time for a new program is the need to obtain enough data to be able to start this decoding. Indeed, in addition to the transmission time required to obtain the entire boot image (type I or IDR), there is added a delay required to be able to display the first decompressed image in due time. If this image is ready too early, the next image may not be completely available yet, either because the data in this next image is not yet transmitted, either because the decoding time has not elapsed or again because the decoded boot image is ahead of its intended presentation time. Once the start-up image is ready to be displayed, it is necessary to wait for enough subsequent images to display the display smoothly.

  It is also necessary to take into account the time required to obtain the decryption key from the access control data transmitted with the stream. Each program can indeed be associated with separate keys. For a transmission of an MPEG2 type transport train, each of these keys is thus constituted by a control word, denoted CW (for Control Word), obtained from authorization control messages, denoted ECM (for Entitlement Control). Messages). The extraction of the control words is performed by the secure access card, during a processing that may require a duration of half-frequency, that is to say commonly between 300 and 400 ms.

  2872987 -4- During the zapping time, no program is usually displayed, since the old one is no longer selected to be demultiplexed, decrypted and decoded, and the new one is not yet available. Usually, the user must therefore undergo a timeout, during which it merely sees on the screen the last image of the previous program or a black screen, until the next program starts. This waiting time is likely to be even higher in the future due to the increased size of the image groups and the decryption complexity (despite improved processing capabilities).

  To reduce this duration, it is conceivable to continue the local broadcast of the current program until the next program becomes available, while displaying for example superimposed on the screen a change of channel message. However, such an embodiment requires an increase in complexity of the digital receiver, and in particular a duplication of several of the functionalities, in particular two tuners. In addition, this solution does not solve the problem of waiting for the next program, and may even be unpleasant if the user wants to immediately stop broadcasting a program before moving on to the next.

  US-5349641 discloses a method of transmitting and receiving conditional access programs with a reduced program switching time. According to this technique, the ECM authorization control messages having verification words changed after each period of time, called phase, are transmitted on the one hand at a first frequency, ECMp main verification messages for an access program. main, and secondly at a second lower frequency, ECMs secondary verification messages for secondary programs (in fact, programs to which the user is likely to zap). The secondary verification messages are transmitted in a single phase, between two successive transmissions of the main verification messages.

  In this way, one avoids having to wait for the ECM message of the program to which one is switching, since this message is already available, and one can even calculate the control word in parallel with the signal acquisition.

  Although the zapping duration is thus reduced, this method nevertheless requires a specific treatment at the emission level. In addition, it requires a mechanism for the identification and continuous storage of ECM messages received throughout the reception of programs.

  The present invention relates to a device for securely demultiplexing multiplexed streams of several programs, making it possible to reduce the zapping duration. Moreover, this device can authorize the exploitation of streams without particular adaptation at the level of the emission, and can make it possible to have to complicate the treatments, only at the moments of the commutations between programs.

  The invention also relates to a digital receiver-decoder, a demultiplexing method and a computer program having the advantages of the device of the invention.

  For this purpose, the subject of the invention is a secure demultiplexing device comprising: means for receiving at least one multiplexed stream of at least two programs intended to be represented to a user, each of these programs comprising at least one program less encrypted representation data and access control data making it possible to decrypt the representation data of this program, - means for demultiplexing the multiplexed stream as a function of a selection of at least one of the programs by the user, the demultiplexing means being provided for extracting at least the access control data and the encrypted representation data of the selected program; means for setting a decryption key for the encrypted representation data; from the access control data, - and means for decrypting the encrypted representation data, by means of this decry key ptage.

  According to the invention, the demultiplexing device comprises: means for storing at least the encrypted representation data of the selected program, in at least one transient storage space, in parallel with setting the decryption key of the data representation by the establishment means, and means for injecting the encrypted representation data of the selected program, the transient storage space to the decryption means when the decryption key is established.

  Representation is a local broadcast for users, including an image display for video and a sound program for audio.

  The means defined in the demultiplexing device must be understood as purely functional entities, which may or may not coincide with physical entities. Several of these means can thus be grouped together in an electronic component or software, and conversely, some of the means can be distributed in several physical entities. This is true also for the preferred embodiments defined below.

  The storage means, designed to store for at least a transient duration the encrypted representation data of the selected program, may be intended to selectively store these data, or on the contrary to store more widely a set of data including these data. representation, such as in particular the whole of the incoming flow.

  They are intended to operate in parallel with the means of establishment, in that at least part of the recording of the representation data in the storage space is carried out while the decryption key is in the process of being established. . Furthermore, the storage means may also operate at other times without the establishment means are in the process of determining the decryption key.

  The demultiplexing means may be located upstream or downstream of the storage means, or possibly both.

  The injection means are intended to transfer the representation data of the transient storage space to the decryption means, optionally with the intermediary of a demultiplexer. The injection is effective when the decryption key is established, which does not exclude that it started before this time of establishment of the key.

  Surprisingly, it is the representation data which is stored in transient storage space, such as a buffer memory, while establishing in parallel the decryption key, then it is to an extraction of the useful data that uses this storage space. This contrasts with the traditional push mode, or push mode, by partially introducing the pull mode, or pull mode.

  This extraction of the representation data from the transient storage space makes possible an accelerated recovery of useful data, such as, in particular, the start-up data of the intra-image type. We can thus significantly reduce the average time of attachment to a new program during a zapping.

  According to a particular embodiment, the demultiplexing device is used to buffer (that is to say, buffer) the data to be decrypted (audio, video and others) during the processing time by an access card. secure of a corresponding decryption ECM message. Once the control word CW for decryption is available, the device is provided for injecting the buffered data into a subset of demultiplexing I decryption with this control word, which offers the correct decryption key.

  In a preferred embodiment of the device of the invention, the demultiplexing means comprise: first demultiplexing means provided for demultiplexing the stream received by the reception means, extracting the encrypted representation data and the control data of accessing the selected program, and sending at least the encrypted representation data to the storage means and the access control data to the establishment means, and the second demultiplexing means provided to receive at least the representation data. encrypted the selected program from the transient storage space by the injection means and transmit the encrypted representation data to the decryption means.

  This embodiment is therefore based on a double demultiplexing, which includes a first and a second demultiplexing respectively upstream and downstream of the storage means. The first demultiplexing makes it possible to extract the appropriate access control data and selectively store transient storage of the data of the targeted program, including in particular the representation data. This part is rather associated with a push mode (reception of data streams). The second demultiplexing makes it possible to distinctly process the various data of the targeted program, retrieved from the storage space by the injection means. This part is rather associated with a mode of pull (recovery of the stored data).

  The set makes it possible to offer an effective reduction of the zapping duration, thanks to an accelerated hooking to the new program (while the key is computed, the representation data gradually becomes available for extracting the startup data and the data. following data). In addition, the additional storage required can be quite small (a small portion of a program for a short time) and makes possible the use of standard components.

  In an alternative embodiment, provision is made for a switchover from the first to the second demultiplexing means, when the decryption key is established and the transient storage space is emptied of its representation data. This variant relies on an injection module injection speed that is higher than the arrival speed of the flow data. It makes possible the use of a single steady state multiplexer, the unused demultiplexing means being then released for other applications. However, its implementation is relatively complex.

  In another preferred embodiment of the device of the invention: the storage means are provided for storing the multiplexed stream in the transient storage space; the demultiplexing means have a first mode of operation in which the means for storing the multiplexed stream in the transient storage space; demultiplexing receive the multiplexed stream from the receiving means, extract the access control data of the selected program and transmit these access control data to the establishment means, and a second mode of operation in which the demultiplexing means receives the multiplexed stream from the transient storage space by the injection means, extracts the encrypted representation data of the selected program and transmits the representation data to the decryption means, and the demultiplexing device comprises means for automatically switching the demultiplexing means of the p first operating mode in the second operating mode when the decryption key is established.

  An interesting feature of this other embodiment is to use the same demultiplexing means to act upstream and downstream of the storage means. Upstream, the demultiplexing means make it possible to extract the access control data from the selected program, and downstream, they make it possible to extract from the transient storage space the data appropriate for this program, such as in particular the video and the audio. The same demultiplexing means can thus operate in the push mode (upstream) and in the pull mode (downstream), switching from one mode to the other being controlled by switching means.

  This embodiment, compared to that of the previous form, requires more storage space, since sorting in the received data stream to focus on the selected program is practiced only downstream of the storage. In addition, compared to standard components, it may require an additional hardware cell, allowing the received stream to be written directly into storage space without passing through a demultiplexing cell.

  According to a further preferred embodiment of the device of the invention, the decryption means comprise first and second decryption means. In addition, the demultiplexing means comprise: first demultiplexing means provided for demultiplexing the stream received by the reception means, extracting the encrypted representation data and the access control data of the selected program, and sending at least the representation data encrypted to the storage means and the access control data to the setting means; second demultiplexing means for receiving at least the encrypted representation data of the selected program from the storage space; transient storage by the injection means and for transmitting the encrypted representation data to the first decryption means, and the third demultiplexing means provided for demultiplexing the stream received by the receiving means, extracting the encrypted representation data and the access control data of the selected program And send at least the representation of encrypted data to the second decryption means and the access control data to the setting means.

  The demultiplexing device also comprises means for switching the first decryption means to the second decryption means for exploiting the decryption representation data, said switching means being designed to operate when the transient storage space is completely emptied by the injection means, encrypted representation data stored in this storage space.

  This embodiment makes possible the use of a single steady-state demultiplexer, the unused demultiplexing means 2872987 -12 being then released for other applications. However, it is relatively difficult to implement because it requires the proper introduction of a transition phase into the inputs of the demultiplexers.

  Preferably, the demultiplexing device comprises detection means for each of the programs, starting data among the program representation data, these startup data making it possible to initiate a representation of the program.

  These detection means may in particular be physically integrated in the demultiplexing means, in one or more decoders (for example audio or video) downstream of the decryption means, or in a central unit. They may also be present in more than one of these entities.

  An identification of the data types of the received stream is generally present at the level of the decoders or the central unit to apply to decrypted streams. However, it is interesting to exploit additional means of upstream detection applying to encrypted streams, which limits the data to be stored and / or transferred.

  Advantageously, the representation data including video data, these detection means are capable of detecting intra-type images.

  Since the representation data is intended to be received by the reception means according to a reception rate, the injection means are preferably capable of injecting these representation data to the decryption means at an injection rate greater than the flow rate. reception.

  In this way, the data put in the transient storage space can be transmitted for processing more quickly than the data arrives in the stream. This makes possible a faster search of the start data and / or decryption and faster decoding to catch a delay in the representation and to represent the representation data decrypted at the right times of representation.

  Advantageously, the demultiplexing device then comprises decrypted representation data decoding means arranged downstream of the decryption means and each of the programs being designed to be represented in real time at a representation rate of the representation data of this program, the decoding means are able to decode the representation data at a decoding rate greater than the representation rate.

  Such decoding of the rhythm greater than unity makes it possible to shorten the processing times of the representation data, when these data become capable of being decrypted after zapping. In practice, preferentially, it is a video decoder that has decoding capabilities at a speed greater than unity.

  With a fast injection, it is also advantageous to have a mechanism for rapid detection of start-up data (such as searching for type I or IDR images). Preferably, the associated detection means are capable of operating at a rate at least equal to that of injection.

  The demultiplexer device is preferably provided for the representation data to comprise audio-visual data. Audiovisual data means audio and / or video data.

  The invention also relates to a digital decoder receiver characterized in that it comprises a demultiplexing device according to any one of the forms of the invention.

  Another object of the invention is a secure demultiplexing method comprising: a step of receiving at least one multiplexed stream of at least two programs intended to be represented to a user, each of these programs comprising at least data encrypted representations and access control data for decrypting the representation data of this program, - a step of demultiplexing the multiplexed stream according to a selection of at least one of the programs by the user, wherein at least the access control data and the encrypted representation data of the selected program are extracted; a step of setting a decryption key of the encrypted representation data from the access control data; and a step of decrypting the encrypted representation data by means of the decryption key.

  According to the invention, the method comprises a step of transient storage of at least the encrypted representation data of the selected program, in parallel with the establishment of the decryption key of the representation data, the decryption step being applied to the data. encrypted representation of the previously selected program stored, when the decryption key is set.

  This demultiplexing method is preferably implemented by means of a device of forms of the invention.

  The invention also applies to a computer program product comprising program code instructions for executing at least the storage step of the demultiplexing method according to the invention, when this program is executed on a program. computer. By computer program product is meant a computer program support, which may consist not only of a storage space containing the program, such as a floppy disk or a cassette, but also a signal, such as a electrical or optical signal.

  The invention will be better understood and illustrated by means of the following examples of embodiment and implementation, in no way limiting, with reference to the appended figures in which: - Figure 1 is a block diagram of a secure demultiplexing device according to the invention; FIG. 2 represents a first embodiment of a demultiplexing device according to FIG. 1; FIG. 3 represents a second embodiment of a demultiplexing device according to FIG. 1; FIG. 4 represents a third embodiment of a demultiplexing device according to FIG. 1; FIG. 5 shows a particular implementation of the demultiplexing device of FIG. 2, in a digital receiver-decoder; FIG. 6 gives the evolutions as a function of the time of the reception of images, the synchronization required for the instants of image display, the decoding of images and the actual display of images, obtained with the device demultiplexing of Figure 4; And Figure 7 shows a particular implementation of the demultiplexing device of Figure 3, in a digital receiver-decoder.

  In Figures 1 to 5 and 7, the modules shown are functional units, which may or may not correspond to physically distinguishable units. For example, these modules or some of them may be grouped into a single component, or be functionalities of the same software. On the other hand, some modules may be composed of separate physical entities.

  Identical or similar elements are designated by the same references, suffixes A, B, C and D can be used for respectively four embodiments described below.

  A secure demultiplexing device 1 (FIG. 1) comprises a reception module 11 of a multiplexed transport stream FTM of several programs, for example television programs. Each of these programs includes CRYP encrypted representation data and CTRL access control data for decrypting the representation data. The demultiplexer device 1 is typically incorporated in a digital receiver-decoder.

  This device 1 also comprises a set of DMX demultiplexing of the FTM stream, according to SELEC selection instructions of one of the programs by a user, responsible for extracting at least the CTRL access control data and the representation data. encrypted CRYP for the selected program. An establishment module 12 has the function of constructing a key CLE (or more) decryption of these encrypted representation data CRYP, from these access control data CTRL.

  A decryption set 13 downstream of the demultiplexing DMX set is provided for decrypting the CRYP encrypted representation data of the selected program, by means of the key CLE obtained by the setting module 12, and to produce Decrypted representation data DECRYP.

  The demultiplexing device 1 also comprises a storage module 14 of at least the encrypted representation data CRYP of the selected program, in a transient storage space 20, such as in particular a buffer memory. This storage module 14 is provided to perform this storage (at least in part) in parallel with the establishment of the decryption key CLE by the establishment module 12.

  An injection module 15 is provided for injecting the encrypted representation data CRYP of the selected program, from the storage space 20 to the decryption unit 13 when the decryption key CLE is established, an SGNL signal being for example transmitted to this effect (directly or not) by the establishment module 12 to the injection module to trigger the injection.

  In the preferred embodiment shown, the demultiplexing device 1 also comprises a startup data detection module 16 for each program, among the representation data of this program. This startup data is used to initiate a program representation (such as a screen display).

  In the illustration embodiment (FIG. 1), the detection module 16 carries out the detection from the storage space 20, and influences the injection module 15. This embodiment is based on unencrypted transport type data. present in the received FTM stream. In other embodiments, the detection module 16 is disposed downstream of the decryption unit 13. Such solutions are used in particular when the FTM stream does not contain decrypted transport type data, which are relevant for the identification of startup data. More specifically, according to a preferred implementation, the detection module 16 is arranged at the video decoding level.

  The demultiplexing device 1, exposed in generic form, will now be developed according to four particularly interesting exemplary embodiments.

  In the first exemplary embodiment (FIG. 2), the device 1 denoted 1A comprises two demultiplexing modules DMX1A and DMX2A composing the demultiplexing assembly DMX. The first demultiplexing module DMX1A is responsible for demultiplexing the received FTM stream by the receiving module 11, extracting the encrypted representation data CRYP and the access control data CTRL of the selected program, and sending at least these CRYP encrypted representation data to the storage module 14 and the access control data CTRL to the establishment module 12. The second demultiplexing module DMX2A is responsible for receiving at least CRYP encrypted representation data of the selected program from the transient storage space 20, by the injection module 15, and transmit the CRYP encrypted representation data to the decryption assembly 13, formed by a decryption module 13A.

  In the second exemplary embodiment (FIG. 3), the device 1 denoted 1B comprises three demultiplexing modules DMX1B, DMX2B and DMX3B making up the demultiplexing assembly DMX, and two decryption modules 13B and 13B 'making up the decryption unit. 13. The decryption module 13B is disposed downstream of the demultiplexing modules DMX1B and DMX2B in series, and the decryption module 13B 'is arranged downstream of the demultiplexing module DMX3B. In addition, the demultiplexer device 1B comprises two additional storage modules 19B and 2872987 -19- 'respectively in temporary storage spaces 30B and 30B' downstream of the decryption modules 13B and 13B '. These spaces 30B and 30B 'are preferably intended to feed decoders.

  In practice, storage modules such as 19B and 19B 'and associated storage spaces 30B and 30B' are preferably provided for each type of component of the FTM flow. For example, two separate pairs of buffers can be provided for the audio and the video respectively (each pair comprising the storage spaces 30B and 30B 'for one of the components), these buffers filling and emptying separately to the rhythm respectively audio or video. Thus, the passage of the downstream storage of the DMX2B demultiplexing module, the downstream storage of the DMX3B demultiplexing module is performed for the audio independently of the video.

  The first DMX1B demultiplexing module is, first of all, responsible for demultiplexing the FTM stream received by the reception module 11, extracting the CRYP encrypted representation data and the access control data CTRL of the selected program, and sending at least this encrypted representation data CRYP to the storage module 14 and the access control data CTRL to the establishment module 12.

  The second demultiplexing module DMX2B is loaded, in a second step, to demultiplex the encrypted representation data CRYP of the selected program from the transient storage space 20, provided by the injection module 15. This step triggers a once the decryption key CLE established (SGNL2 signal of the establishment module 12) and transmitted to the decryption module 13B, and the second demultiplexing module DMX2B configured. In operation, the latter thus provides the CRYP encrypted representation data to the decryption module 13B, which decrypts the received data and transmits the DECRYP decrypted data to the storage module 19B, which provisionally places them in the storage space 30B before operation. This space 30B is the one used downstream until the contrary instruction.

  The third DMX3B demultiplexing module is responsible for demultiplexing the FTM stream received by the reception module 11, once the decryption key has been established (signal SGNL3 of the establishment module 12) and transmitted to the decryption module 13B '. It is intended to extract the CRYP encrypted representation data and the CTRL access control data from the selected program, and to send the access control data CTRL to the establishment module 12 and the CRYP encrypted representation data to the decryption module 13B '. In operation, the latter decrypts the received data and transmits the DECRYP decrypted data to the storage module 19B ', which provisionally places them in the storage space 30B' before operation. This space 30B 'is used downstream only after explicit instruction (previously, only the space 30B provides the data to be exploited).

  A function synchronization implementation allows the DMX1B, DMX2B and DMX3B demultiplexers to be evaluated over time. To do this, the establishment module 12 is responsible for provoking when the decryption key CLE is available, in addition to the activation of the demultiplexing modules DMX2B and DMX3B, the release of the demultiplexing module DMX1B. In the embodiment described, the establishment module is also provided to communicate the key CLE at the same time to the two demultiplexing modules DMX2B and DMX3B, as soon as it is determined.

  In addition, the demultiplexer device 1B comprises a switching assembly 18, intended to act during a first transition 2872987 -21when the CRYP encrypted representation data recorded in the transient storage space 20 are completely consumed, and when a second transition when the storage space 30B is emptied. During the transition phase between the establishment of the decryption key CLE by the establishment module 12 and the complete emptying of the storage space 30B, the same key CLE is used in the two decryption modules 13B and 13B .

  During the first transition, the switching assembly 18 is provided to release the second DMX2B demultiplexing module as well as the storage space 20. Thus, once recovered all CRYP encrypted representation data stored in the storage space 20, only the third demultiplexer DMX3B continues the demultiplexing. In practice, it is therefore sufficient to use simultaneously among the demultiplexers, first DMX1B only, then only DMX2B and DMX3B, then only DMX3B.

  During the second transition (empty storage space 30B), the switching assembly 18 is provided to activate the output of the storage space 30B 'and to disable the output of the storage space 30B, and to cause the once a deactivation of the decryption module 13B and an activation of the decryption module 13B '(action arrow not shown in Figure 3).

  The key establishment time CLE is distinct from a period crypto duration determined by a program broadcaster and an access control provider. In general, the latter is worth several times the establishment time of the key CLE.

  It is more precisely considered for the reliability of the system that the duration of validity of the decryption keys is sufficient to cover all the demultiplexing operations taking place in the DMX2B and DMX3B demultiplexers during the transition phase, so as to that the same CLE decryption key can be used throughout the process associated with this phase.

  In addition, the transition is easily accomplished when the demultiplexing functions are able to change their stream input with the accuracy of a packet. Only one single steady-state demultiplexer is needed.

  In the third embodiment, which can be derived from the first example (FIG. 2), the first demultiplexing module DMX1A is used only during the filling phases of the storage space 20 (parallel to the establishment of the key decryption CLE) and emptying the contents of this space 20 by the injection module 15. An injection speed is chosen by the injection module 15 higher than the data arrival speed of the FTM flow. Then there comes a time when the storage space 20 no longer contains CRYP encrypted representation data.

  At this time, the demultiplexing module DMXIA is deleted and the FTM stream is directly connected to the second demultiplexing module DMX2A. The CTRL control data is then retrieved by the latter.

  This embodiment can be easily obtained as soon as the demultiplexing functions are able to change their stream input with the precision of a packet. As for the second example, only one single steady-state demultiplexer is needed.

  In the fourth exemplary embodiment (FIG. 4), the DMX demultiplexing assembly of the demultiplexing device 1, denoted ID, is reduced to a single DMX-D demultiplexing module, and the storage module 14 is designed to store the stream. FTM received in the storage space 2872987 -23transitoire 20. The DMX-D demultiplexing module has two modes of operation: - a first mode in which the DMX-D demultiplexing module receives the FTM stream from the module input 11, extracts the access control data CTRL and transmits the latter to the establishment module 12, and a second mode in which the demultiplexing module DMX-D receives the FTM stream from the storage space by the injection module 15, extracts the encrypted representation data CRYP of the selected program and transmits them to a decryption module 13D forming the decryption unit 13.

  In addition, the demultiplexing device 1 D comprises a switching module 17 of the demultiplexing module DMX-D, from the first to the second operating mode when the decryption key CLE is established (the switching module 17 then receiving for example a signal SGNL 'of the establishment module 12).

  The first embodiment (Figure 2) is detailed below with reference to a particular implementation (Figure 4). In this implementation, the demultiplexing device 1A is integrated with a digital receiver-decoder 10, denoted 10A, of audiovisual streams. It comprises: a tuner / demodulator 21 receiving the FTM stream, the first DMXIA demultiplexing module at the output of the tuner / demodulator 21, in the form of a demultiplexer programmed to extract identification information from a service; this translates for example for an MPEG2 stream by the search for a program allocation table or PAT (for Program Allocation Table) describing a list of services or programs available in a transport stream, then a distribution table of program or PMT (for Program Map 2872987 -24Table) describing a list of audio, video, decryption data, or other data specific to the programs in question; this demultiplexer is programmed to extract unencrypted FONC operating data and the decryption data constituting the access control data CTRL in the form of ECM messages; the temporary storage space 20 at the output of the first demultiplexing module DMX1A, in the form of a buffer memory, designed to receive a partial transport stream containing only the components of the audio, video and other data streams to be decrypted, acquired by the module demultiplexing DMXIA (the storage module 14 is here functionally included in the demultiplexing module DMX1A); the injection module 15, having an input connected to the storage space 20 and an output connected to the second demultiplexing module DMX2A; the second DMX2A demultiplexing module, programmed with component identifiers used to construct the partial stream in the first DMXIA demultiplexing module; two data paths go downstream of this demultiplexing module DMX2A: a first path CH1 without decryption for unencrypted data, and a second path CH2 for encrypted data, leading to the decryption module 13A; the establishment module 12 in the form of a receiver module 12A of a secure access card designed to receive the access control data CTRL; as soon as the components conveying these data are available, they are provided to the access card which initiates the extraction of the control word (s) CW, able to serve as decryption key CLE for each of the audio components, video , or other type, to decrypt; the decryption module 13A downstream of the demultiplexing module DMX2A, designed to receive from the establishment module 12 the CLE keys made available; once this operation is completed and the programmed DMX2A demultiplexing module is programmed, the data injection mechanism can start and provide data to this DMX2A demultiplexing module; the second demultiplexing module DMX2A and the decryption module 13A form a demultiplexing and decrypting cell 22 which produces unencrypted video, audio and operating data FONC2; a video decoder 26 receiving the decrypted video data of the cell 22; an audio decoder 27 receiving the decrypted audio data of the cell 22; - and a central unit 25.

  A Type I (or IDR) detection mechanism for the JVT standard is implemented in the second demultiplexing module DMX2A, one of the decoders 26 or 27, or the central unit 25.

  In the preferred example shown, suitable processing rates are available as follows: the injection module 15 is able to inject data at a higher rate than the original flow of the components of the received FTF stream ; the type I or IDR image search mechanism operates at a rate at least equal to the injection speed by the injection module 15; and the video decoder 26 makes it possible to decode images faster than the unit.

  This implementation makes it possible to anticipate the synchronization required for the times of presentation of the decoded images. Indeed, the data stored in the storage space 20 is consumed more quickly than the data arrives with the FTM stream.

  The time flow processes of the image processing to be displayed using the digital receiver-decoder 10A will now be discussed in more detail (Figure 6).

  The incoming FTM stream is for example formed of an MPEG2 multiplex, which comprises a succession of groups of images 11, 12, 13 ... arriving during the time t (axis 30), each group of images being initiated by an image intra 10. This succession thus forms a picture chain C11 formed of successive sequences SEQ1, SEQ2. In practice, the decoder receiver 10A receives a program change instruction and begins to identify the appropriate decryption components (ECM messages ) at a time tO.

  The ECM messages associated with the targeted program are received with the incoming FTM stream and are exploited by the secure access card to determine the CLE decryption key. This is obtained after a processing time DT, at a time t1. In addition, successive display instants of the received images are transported as synchronization data in the FTM stream. They define a chain of synchronized images CI3, which is the one required for the display of sequences SEQ1, SEQ2 ...

  According to the conventional method, after obtaining the key CLE, the digital receiver would wait for the next beginning of sequence. The latter would intervene here with the arrival of the intra IO image of the sequence SEQ2 after a waiting period DA, at a time t3. The received image chain Cl2 from this instant t3 would then be able to decode the images and display them at the expected display times, the first decoded image (intra-10 image) to be ready at a time t4.

  With the receiver-decoder 10A, the encrypted video data received are stored in the storage space 20 (they are buffered) as and when they are received (image chain CI4).

  The availability of the CLE key initiates the boot image detection step and the decryption and decoding steps. Thus, after a search phase start sequence RD, an image chain CI5 corresponding to the decoding of the image sequences over time. In the example shown, the intra-10 image of the current sequence SEQ1 was received and buffered during the establishment of the key CLE.

  The actual display of the decoded images (CI6 image chain, identical to the CI3 image chain) is only performed as soon as the images become available in time relative to the predicted display times. Thus, the first decoded images I-Tard, ready too late, are not displayed (here, 10, 11 and 12 of the sequence SEQ1). After a reset time DR relative to the required times, the first decoded image in time is displayed (here the image 14 of the sequence SEQ1 at a time t2).

  Later, the following sequence is received and then displayed (here, the sequence SEQ2 begins to be received at a time t3 and must begin to be displayed at a time t4).

  In the end, the display duration gained during the zapping, compared to an attachment that would be done conventionally on the intra image received for the following sequence (here, the image IO of the sequence SEQ2), is a duration GAIN given by the difference between times t4 and t2.

  The second exemplary embodiment (FIG. 3) is detailed below with reference to a particular implementation (FIG. 7). In 2872987 -28this implementation, the demultiplexing device 1B is integrated in a digital receiver-decoder 10, noted 10B, audiovisual streams. This includes (elements identical or similar to those of the first example are not detailed) - the tuner / demodulator 21 receiving the FTM stream; the first DMX1B demultiplexing module at the output of the tuner / demodulator 21; the encrypted data extracted by this module goes to the decryption module 13B; the temporary storage space 20 at the output of the first demultiplexing module 10 DMX1 B; the injection module having an input connected to the storage space and an output connected to the second demultiplexing module DMX2B; the second demultiplexing module DMX2B, downstream of the injection module 15; the third demultiplexing module DMX3B, having an input connected to an output of the tuner / demodulator 21 (FTM stream); the establishment module 12 in the form of a receiver module 12B of a secure access card, for receiving the access control data CTRL and extracting the control words CW; the decryption modules 13B and 13B 'downstream of the demultiplexing modules DMX2B and DMX3B, designed to receive from the establishment module 12 the CLE keys made available; once this operation is completed and the third demultiplexing module DMX3B programmed to demultiplex the FTM stream coming from the tuner / demodulator 21, the data injection mechanism starts and provides data to the second demultiplexing module DMX2B and the corresponding decryption module 13B ; the latter then produce unencrypted video, audio and operating data FONC1 which are transferred into the storage space 30B consisting of several buffers, in particular audio and video (the storage module 19B is here 2872987 -29 integrated with the decryption module 13B); the third demultiplexing module DMX3B and the corresponding decryption module 13B 'produce unencrypted audio, video and operating data FONC2 and supply them to the storage space 30B', consisting of several buffers; the video decoder 26 receiving the decrypted video data of the portion of the storage spaces 30B corresponding to the video buffers; the audio decoder 27 receiving the decrypted audio data 10 of the part of the storage spaces 30B corresponding to the audio buffers; a source choice switch 28 for the access control data CTRL (this source may be the DMX1B or DMX3B demultiplexing module) destined for the secure card, forming part of the switching module 18; - and the central unit 25.

  A type I or IDR image detection mechanism is implemented in the second and third demultiplexing modules DMX2B and DMX3B, one of the decoders 26 or 27, or the central unit 25.

  Preferably, appropriate processing rates are available, as in the particular implementation of the first exemplary embodiment (FIG. 5).

  A particular implementation of the fourth exemplary embodiment (FIG. 4) leads to the following step process: transfer of the complete FTM transport stream both in a demultiplexing and decryption cell (DMX-B demultiplexing and decryption modules 13) and in the storage space 20; extracting the CTRL access control data and transmitting it to a secure access card (establishment module 12); 2872987 -30- - once the CW control words made available by the secure access card, configuration of the decryption module 13 of the demultiplexing cell and decryption and switching of the output of the storage space 20 to this cell ; at this time, the FTM stream is only transferred into the storage space 20 and no longer directly to the demultiplexing and decrypting cell; - extraction of scrambled streams such as video and audio by the demultiplexing and decryption cell.

Claims (12)

-31-CLAIMS   A secure demultiplexing device (1) comprising: - means for receiving (11) at least one multiplexed stream (MTF) of at least two programs intended to be represented to a user, each of said programs comprising at least two programs encrypted representation data (CRYP) and access control data (CTRL) for decrypting said representation data of said program; - demultiplexing means (DMX) of said multiplexed stream (FTM) according to a selection of at least one of said programs by said user, said demultiplexing means (DMX) being provided for extracting at least the access control data (CTRL) and the encrypted representation data (CRYP) from said selected program, - means for setting (12) a decryption key (CLE) of said encrypted representation data (CRYP) from said access control data (CTRL), and decrypting means (13) of said encrypted representation data (CRYP), by means of said decryption key (CLE), characterized in that said device (1) comprises: storage means (14) of at least the encrypted representation data (CRYP) ) of said selected program, in at least one transient storage space (20), in parallel with the establishment of said decryption key (CLE) of said representation data (CRYP) by the setting means (12), - and injection means (15) of said encrypted representation data (CRYP) of said selected program, said transient storage space (20) to the decryption means (13) when said decryption key (CLE) is established .   2. demultiplexing device (1A) according to claim 1, characterized in that said demultiplexing means (DMX) comprises: - first demultiplexing means (DMX1A) for demultiplexing said stream (FTM) received by the receiving means (11), extracting the encrypted representation data (CRYP) and the access control data (CTRL) of said selected program, and sending at least said encrypted representation data (CRYP) to said storage means (14) and access control data (CTRL) to said setting means (12); and second demultiplexing means (DMX2A) for receiving at least said encrypted representation data (CRYP) of said selected program from said transient storage (20) by the injection means (15) and for transmitting said encrypted representation data (CRYP) to the decryption means (13A).   3. demultiplexing device (1D) according to claim 1, characterized in that: - said storage means (14) are provided for storing said multiplexed stream (FTM) in said transient storage space (20), - the means for demultiplexing (DMX) have a first mode of operation wherein said demultiplexing means receives said multiplexed stream (MTF) from the receiving means (11), extracts the access control data (CTRL) of said selected program and transmits said access control data (CTRL) to the setting means (12), and a second operating mode in which said demultiplexing means (DMX) receives said multiplexed stream (FTM) from said storage space transient (20) by the injection means (15), extract the encrypted representation data (CRYP) of said selected program and transmit said representation data to the means of decryption (13D), - and said demultiplexing device (1D) comprises means for automatic switching (17) of the demultiplexing means (DMX) of the first operating mode to the second mode of operation when said decryption key (CLE) is established.   4. Demultiplexing device (1B) according to claim 1, characterized in that said decryption means (13) comprise first (13B) and second (13B ') decryption means, in that said demultiplexing means (DMX) ) comprise: - first demultiplexing means (DMX1B) intended for demultiplexing said stream (FTM) received by the receiving means (11), extracting the encrypted representation data (CRYP) and the access control data (CTRL) said selected program, and sending at least said encrypted representation data (CRYP) to said storage means (14) and the access control data (CTRL) to said setting means (12), - second means of demultiplexing (DMX2B) provided to receive at least said encrypted representation data (CRYP) of said selected program from said transient storage space (20) by the injection means (15) and for trans putting said encrypted representation data (CRYP) to the first decryption means (13B), and third demultiplexing means (DMX3B) provided for demultiplexing said stream (FTM) received by the receiving means (11), extracting the data of encrypted representation (CRYP) and the access control data (CTRL) of said selected program, and send at least said encrypted representation data (CRYP) to the second decryption means (13B ') and the data access control system (CTRL) to said setting means (12), and in that said demultiplexing device (1 B) comprises tilting means (18) of the first decrypting means (13B) to the second means decryption device (13B ') for exploiting the decryption representation data (DECRYP), said switching means (18) being provided for operation when said transient storage space (20) is fully empty by the injection means (15) said encrypted data representation (CRYP) stored in said storage space (20).   5. demultiplexing device (1) according to any one of the preceding claims, characterized in that said demultiplexing device comprises detection means (16) for each of said programs, starting data (I, ldr) among said data representation of said program, said startup data for initiating a representation of said program.   6. demultiplexing device (1) according to claim 5, characterized in that said representation data (CRYP) including video data, the detection means (16) are capable of detecting intra-type images (I, Idr) .   7. demultiplexing device (1) according to any one of the preceding claims, characterized in that said representation data (CRYP) being provided to be received by the receiving means (11) at a reception rate, the means of injection (15) are capable of injecting said representation data to the decryption means (13) at an injection rate greater than said reception rate.   2872987 -35- 8. demultiplexing device (1) according to claim 7, characterized in that it comprises decoding means (26, 27) of said decrypted representation data (DECRYP), arranged downstream of the decryption means (13) and each of said programs being designed to be represented in real time at a representation rate of the representation data of said program, the decoding means (26, 27) are able to decode said representation data at a decoding rate greater than the bit rate of representation.   9. demultiplexing device (1) according to any one of the preceding claims, characterized in that said demultiplexing device is provided so that the representation data comprises audiovisual data.   10. digital decoder receiver (10) characterized in that it comprises a demultiplexing device (1) according to any one of claims 1 to 9.   11. Secure demultiplexing method comprising: a step of receiving at least one multiplexed stream (FTM) of at least two programs intended to be represented to a user, each of said programs comprising at least encrypted representation data (CRYP); ) and access control data (CTRL) for decrypting said representation data of said program, - a step of demultiplexing said multiplexed stream (FTM) according to a selection of at least one of said programs by said user, wherein at least the access control data (CTRL) and the encrypted representation data (CRYP) of said selected program are extracted, a step of setting a decryption key (CLE) of said data of an encrypted representation (CRYP) from said access control data (CTRL), and a step of decrypting said encrypted representation data (CRYP), by in said decryption key (CLE), characterized in that said method comprises a step of transient storage of at least the encrypted representation data (CRYP) of said selected program, parallel to the establishment of said decryption key (CLE ) of said representation data (CRYP), the decryption step being applied to said encrypted representation data (CRYP) of the previously selected program stored, when the decryption key (CLE) is established, said demultiplexing method being preferentially implemented implemented by means of a secure demultiplexing device (1) according to any one of claims 1 to 10.   Computer program product, characterized by comprising program code instructions for executing at least the storage step of the access control method according to claim 11 when said program is executed. on a computer.