Abstract:
A method for secure distribution of an original audiovisual stream to a plurality of consumer devices through a multicast session includes generating a protected audiovisual stream by modifying the original audiovisual stream; a complementary stream of any format including digital information suitable to allow reconstruction of an audiovisual stream from the protected stream; calculating a first mark as function of a unique identifier of a receiving consumer device or an external secure device; calculating on the receiving consumer device a first marked audiovisual stream from the protected stream as function of the first mark and the complementary stream; transmitting the protected stream from the receiving device to the second device; calculating a second mark as function of a unique identifier of a second device, an external secure device or a consumer using the second device; and calculating on the second consumer device a second marked audiovisual stream from the protected stream received from the receiving device as function of the second mark.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure generally relates to a secure distribution of multimedia content, more specifically to a method and system for secure sharing among various personal user devices of recorded copies of a multicast audiovisual program, the legal consumption of the recoded audiovisual program being guaranteed by an innovative approach using scrambling and watermarking techniques. 
       BACKGROUND 
       [0002]    Increasing deployment of digital television (satellite, cable and radio broadcast, as well as more recently IP multicast) provides more flexible content consumption on client side. Consumers may record television programs to watch them later to the diffusion time, or to make permanent private copies that can be used on any of their personal home devices. Sharing these copies with family or friends is another feature highly demanded by the digital TV subscribers. 
         [0003]    However, these new services must guarantee the rights granted by the content owners or the service providers, as well as it must prevent any illegal usage and identify the successful hacking attempts. 
         [0004]    To securely implement this kind of system, various technologies are known by the skilled man. 
         [0005]    DTCP (Digital Transmission Content Protection) is a technical specification for copy protection of copyrighted content that is transferred over digital interfaces to personal home devices. Under this specification, digital content can be shared securely between devices in a user&#39;s home but not shared with third-parties outside the home network. Using an authentication scheme, DTCP allows the user to designate devices in the home network as trusted destinations that can transfer data back and forth. 
         [0006]    However, the disadvantage of this technology is that a malicious user may circumvent the DTCP security measures by designing a “fake” device as being part of his home network and to use it not only to illicitly consume the content, but even worse, to illegal distribute the content. 
         [0007]    Another disadvantage is that DTCP specifies that the content should be encrypted before being transmitted to other personal home devices. This requires more expensive personal home devices, so limiting the deployment of such a system. 
         [0008]    CPCM (Content Protection and copy Management) is a part of DVB (Digital Video Broadcast) specification. CPCM addresses the protection of audiovisual content after it has been received by a consumer device. Once the audiovisual content is received by a CPCM-compliant device, it is protected by various cryptographic techniques and a license containing the consumption rights is bound to protected content. Therefore, the protected content can be rendered by other CPCM-compliant devices, with respect to the usage rights stored within the content. 
         [0009]    While being two different technologies (CPCM is focusing on content protection and DTCP on transport link protection), CPCM suffers from the same disadvantages than DTCP: no possibility to identify the successful hacking attempts and complex and costly home devices to be deployed. 
         [0010]    It could be helpful to resolve these disadvantages by marking the content with unique marks for every consuming devices to allow a later identification of eventual hacking attempts, while proposing a simpler protection system that requires a unique operation of content protection applied only once on the server side. 
       SUMMARY 
       [0011]    A method is provided for the secure distribution of an original audiovisual stream to a plurality of consumer devices through a multicast session, the method comprising the steps of generating:
       a protected audiovisual stream by modifying the original audiovisual stream;   a complementary stream of any format comprising digital information suitable to allow reconstruction of an audiovisual stream from the protected stream;
 
and the steps of:
   calculating a first mark as function of a unique identifier of a receiving consumer device or an external secure device;   calculating on the receiving consumer device a first marked audiovisual stream from the protected stream as function of the first mark and the complementary stream;   transmitting the protected stream from the receiving device to the second device;   calculating a second mark as function of a unique identifier of a second device, an external secure device or a consumer using the second device;   calculating on the second consumer device a second marked audiovisual stream from the protected stream received from the receiving device as function of the second mark.       
 
         [0019]    According to particular aspects:
       to generate the protected audiovisual stream uses cryptographic algorithms;   to generate the protected audiovisual stream uses the specifications DVB-CA;   the protected stream has the same format as the original stream;   to generate the protected audiovisual stream comprises replacing at least one part of the original audiovisual stream with different data in the protected audiovisual stream and storing the replaced parts within the complementary stream;   to calculate the first or the second marked audiovisual stream comprises the steps of:
           descrambling the protected audiovisual stream using the information contained in the complementary stream by generating a clear content stream with similar visual and audible representation as the original content;   generating the first or second marked audiovisual stream by marking the clear content stream in function of the first mark or the second mark respectively;   
           to calculate the first or second marked audiovisual stream comprises the steps of:
           generating a marked complementary stream by marking the complementary stream using the first mark or the second mark respectively;   generating the first or second marked audiovisual stream by descrambling the protected content stream using the information contained in the marked complementary stream;   
           to generate the marked complementary stream is done on a remote server and the marked complementary stream is transmitted from the remote server to the second device;   the complementary stream is transmitted from the receiving device to the second device using a direct-connection link;   the complementary stream is transmitted from the receiving device to the second device using an external secure device;   the complementary stream is transmitted from a remote to the second device using a network connection;   the first mark is generated by the receiving device;   the first mark is generated on an external secure device and transmitted to the receiving device using a direct-connection link;   the second mark is generated on the receiving device transmitted to the second device using a direct-connection link;   the second mark is generated on the receiving device transmitted to the second device using an external secure device;   the second mark is generated on an external secure device and transmitted to the second device using a direct-connection link;   the second mark is generated on the second device;   the transmission and/or storage of the complementary stream is protected by cryptographic means, and   the transmission and/or storage of the marked complementary stream is protected by cryptographic means.       
 
         [0042]    We also provide a device comprising:
       means to generate a protected audiovisual stream by modifying the original audiovisual stream;   means to generate a complementary stream of any format comprising digital information suitable to allow reconstruction of an audiovisual stream from the protected stream;   means to calculate a first mark as function of a unique identifier of a receiving consumer device or an external secure device;   means to calculate on the receiving consumer device a first marked audiovisual stream from the protected stream as function of the first mark and the complementary stream;   means to transmit the protected stream from the receiving device to the second device;   means to calculate a second mark as function of a unique identifier of a second device, an external secure device or a consumer using the second device;   means to calculate on a second consumer device a second marked audiovisual stream from the protected stream received from the receiving device as function of the second mark.       
 
         [0050]    According to particular aspects:
       the system comprises cryptographic means to generate the protected audiovisual stream;   the system comprises means to replace at least one part of the original audiovisual stream with different data in the protected audiovisual stream and means to store the replaced parts within the complementary stream;   the system comprises:
           means to descramble the protected audiovisual stream using the information contained in the complementary stream by generating a clear content stream with similar visual and audible representation as the original content;   means to generate the first or second marked audiovisual stream by marking the clear content stream in function of the first or second mark, respectively;   
           the system comprises:
           means to generate a marked complementary stream by marking the complementary stream using the first or second mark, respectively;   means to generate the first or second marked audiovisual stream by descrambling the protected content stream using the information contained in the marked complementary stream;   
           system comprises means to generate the marked complementary stream and to transmit it to the second device;   system comprises means an external secure device to transmit the complementary stream from the receiving device to the second device;   system comprises a remote server to transmit the complementary stream to the second device;   system comprises an external secure device to generate/store the first or second mark;   system comprises an external secure device to transmit/store the first or second mark to the receiving device or to the second device, respectively;   the receiving device is a computer, a set-top-box, a media center, a mobile phone, a PDA, a portable media player or any other hardware device with multimedia capabilities;   the device is a computer, a set-top-box, a media center, a mobile phone, a PDA, a portable media player or any other hardware device with multimedia capabilities;   the external secure device is a SIM card, secure USB device or any other secure hardware/software component capable to securely store and transmit a unique identifier; and   a USB connection, a wireless network, a wired network, an external hard-disk, a flash disk, an USB key or a CD/DVD devices to allow the transfer of the protected audiovisual stream and/or the complementary stream.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0068]    The above described aspects will become more apparent by describing in detail examples thereof with reference to the attached drawing figures, wherein: 
           [0069]      FIGS. 1A and 1B  show the detailed server side of a multicast system to securely deliver multimedia content; 
           [0070]      FIGS. 2A ,  2 B and  2 C show the detailed client side of a multicast system to securely deliver multimedia content presented in  FIGS. 1A and 1B ; and 
           [0071]      FIGS. 3A ,  3 B and  3 C detail the descrambling module situated on client side for the multicast systems presented in  FIGS. 2A ,  2 B and  2 C. 
       
    
    
     DETAILED DESCRIPTION 
       [0072]    Hereinafter, certain representative examples will be described in detail with reference to the accompanying drawing figures. 
         [0073]    In the following description, the matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the disclosure. Thus, it is apparent that our methods and systems can be carried out without those defined matters. Also, well-known functions or constructions are not described in detail since they would obscure the systems and methods in unnecessary detail. 
         [0074]    In addition, identical references within the accompanying drawing figures address similar technical elements, unless a different meaning is clearly described. 
         [0075]      FIG. 1A  is a structured view of a protection system comprising: a multicast content distribution server  11 , a receiving device  12  to playback the content distributed by the server  11  and a second device  13  to playback the content transmitted by the receiving device  12 . 
         [0076]    The multicast content distribution server  11  has two main functions: to protect the input content and to send it to dynamic user group by broadcast techniques. 
         [0077]    The original content stream  1  is a multimedia stream containing video and audio flows, as well as rich media flows. 
         [0078]    The audiovisual compression methods are the ones well known such as the standard ones: MPEG-2, MPEG-4 part 2, MPEG-4 AVC/H.264, MPEG-4 SVC etc. or the ones largely used by industry: Windows Media Audio and Video, VP6 and the like. 
         [0079]    The structure of the original content stream  1 , as well as all the other mechanisms allowing mixing various audio and visual streams and signaling of codec types, stream types and private data, are standard: MPEG-2 TS, MP4 file format etc. or proprietary: FLV (Flash Video) file format, ASF (Advanced Systems Format) file format and the like. 
         [0080]    The original content stream  1  is scrambled by a scrambling module  2  that generates as output a protected stream  121  and a complementary stream  122  that comprises the information needed by a descrambling component  21  to generate marked contents  124  and  127  from the protected stream  121  in function of a first mark  511 , respectively, a second mark  512 . 
         [0081]    The format of the complementary stream  122  can either be proprietary, either standard, for example, of the same standard as the format of the protected stream  121 . 
         [0082]    According to one aspect, the protected stream  121  and the complementary stream  122  are generated by the scrambling module  2  by using various cryptographic mechanisms known in the art as, for example, the specifications DVB-CA (see ETR 289). 
         [0083]    According to one aspect, the technique that allows the protected stream to have the same format as the original stream, is to exploit different parameters of the audiovisual standards that would impose to a decoder to skip (so not to decode)-the modified data contained within the protected stream. For example, for the video data encoded further to H.264 standard, a modified NALU that is a part of the protected stream is skipped by a standard decoder if the value of the NALU_type field is set to 0 or starting with 24 to 31. Skipping the modified NALU of the protected stream allows the user to have access to a degraded representation of the protected content (as only the unmodified NALU will be decoded), that will not allow to the user to consume it, but that will prompt the user to purchase the content to visualize with a proper quality. 
         [0084]    According to another aspect, the protected stream  121  and the complementary stream  122  are generated by the scrambling module  2  by replacing some parts of the original content stream  1  with different data and thus generating the protected stream content compliant with the format of the original content stream  1 , and storing the original replaced parts within the complementary stream  122 . This method is described in various documents, e.g., WO 2005/032135, the subject matter of which is incorporated herein by reference. 
         [0085]    According to one aspect, the generated streams  121  and  122  are distributed to a dynamic group of receivers by transmission device  4  using one multicast session for both streams. 
         [0086]    According to one aspect, the transmission device  4  integrates DVB MUX functions to multiplex and/or transmit the generated streams  121  and  122 . 
         [0087]    According to another aspect, the generated streams  121  and  122  are distributed to a dynamic group of receivers by transmission device  42  and respectively  43  using separate multicast sessions for each stream. 
         [0088]    According to one aspect, the transmission devices  43  and/or  42  integrate DVB MUX functions to multiplex and/or transmit the generated streams  121  and  122 . 
         [0089]    According to one aspect, the transmission of the complementary stream  122  is protected by various well known cryptographic means. For example, the complementary stream  122  is protected implementing the specifications DVB-CA (see ETR 289). 
         [0090]    On the client side, the receiving device  12  get the protected stream  121  and the complementary stream  122  through the network interface  41 . 
         [0091]    The receiving device  12  is a computer, a set-top-box, a media center, a mobile phone, a PDA, a portable media player or any other hardware device with multimedia capabilities. 
         [0092]    The network interface  41  is an IP (Internet Protocol), cable, terrestrial, satellite or mobile network interface, depending on which kind of network the two streams are transmitted. 
         [0093]    The two streams are then processed by the descrambling module  21  to generate the first marked content  124  in function of a first mark  511 . The functions of the descrambling module  21  will be described later ( FIG. 3A ). 
         [0094]    The first marked content  124  is then transmitted to the multimedia decoding interface  6  for decoding and rendering. 
         [0095]    The multimedia decoding interface  6  is a software/hardware module performing audiovisual decoding, a multimedia player or an external device with various capabilities in terms of multimedia decoding and rendering. 
         [0096]    The protected content  121  is transmitted from receiving device  12  to the second device  13  by direct-connection (e.g., USB connection), network transport (e.g., wireless or wired) or external storage medium (e.g., external hard-disk, flash disk, USB key or CD/DVD). 
         [0097]    The second device  13  is a computer, a set-top-box, a media center, a mobile phone, a PDA, a portable media player or any other hardware device with multimedia capabilities. 
         [0098]    On the second device  13 , the protected content  121  and the complementary stream  122  are then processed by the descrambling module  21  to generate the second marked content  127  in function of a second mark  512 . 
         [0099]    The second marked content  127  is then transmitted to the multimedia decoding interface  61  for decoding and rendering. 
         [0100]    The multimedia decoding interface  61  is a software/hardware module performing audiovisual decoding, a multimedia player or an external device with various capabilities in terms of multimedia decoding and rendering. 
         [0101]      FIG. 1B  is a structured view of an alternative protection system. The difference from the protection system presented within the  FIG. 1A  is that the original content stream  1  is processes by the pre-marking module  3 , and not by the scrambling module  2 . 
         [0102]    The pre-marking module  3  analyses the original content stream  1  and generates 2 streams: a pre-marked content stream  131 , having the same audiovisual representation as the original content stream  1 , and a marking metadata stream  132  comprising the information needed to generate marked contents  124  and  127  from the pre-marked content stream  131  in function of a first mark  511 , respectively a second mark  512 . 
         [0103]    According to one aspect, the pre-marked content stream  131  and the marking metadata stream  132  are generated as described in WO 99/65241, the subject matter of which is incorporated herein by reference. 
         [0104]    The pre-marked content stream  131  and the marking metadata stream  132  are processed by the scrambling module  2  to generate a protected stream  121  and a complementary stream  122  that comprises the information needed by a descrambling component  21  to generate marked contents  124  and  127  from the protected stream  121  in function of a first mark  511 , respectively, a second mark  512 . 
         [0105]    The protected stream  121  and then complementary stream  122  are then processed on the receiving device  12  by the descrambling module  21  to generate the first marked content  124  in function of a first mark  511 . The functions of the descrambling module  21  will be described later ( FIG. 3B ). 
         [0106]      FIG. 2A  details the functioning of the receiving device  12  and the second device  13  while processing the protected content  121  and the complementary stream  122  generated as described by  FIGS. 1A and 1B . 
         [0107]    The first mark  511  is generated by a mark generator  5 . 
         [0108]    The mark generator  5  is a SIM card, secure USB device or any other secure hardware/software component capable to securely store a unique identifier to generate the first mark  511 . 
         [0109]    The first mark  511  comprises a value allowing the unique identification of the receiving device  12  (e.g., SIM card ID), one of the hardware/software components of the receiving device  12  (e.g., a built-in value in a chipset). In addition, the first mark  511  may comprise an identifier of one of the operations related to the protected content  121  (e.g., the date/time of the consumption of the protected content stream  121 , the acquisition/reception of the protected content stream  121 , etc.). 
         [0110]    The complementary stream  122  is transmitted form the receiving device  12  to the second device  13  to allow the consumption of the protected content stream  121  on the second device  13 . 
         [0111]    The complementary stream  122  is transmitted from receiving device  12  to the second device  13  by a direct-connection (e.g., USB connection), network transport (e.g., wireless or wired) or by any other external storage medium (e.g., external hard-disk, flash disk, USB key or CD/DVD). 
         [0112]    According to one aspect, the transmission of the complementary stream  122  from receiving device  12  to the second device  13  is protected by various well known cryptographic means. 
         [0113]    The second mark  512  is generated by a mark generator  51 . 
         [0114]    The mark generator  51  is a SIM card, secure USB device or any other secure hardware/software component capable to securely store a unique identifier to generate the first mark  512 . 
         [0115]    The second mark  512  comprises a value allowing the unique identification of the second device  13  (e.g., SIM card ID), one of the hardware/software components of the second device  13  (e.g., a built-in value in a chipset). In addition, the second mark  512  may comprise an identifier of one of the operations related to the protected content  121  (e.g., the date/time of the consumption of the protected content stream  121 , the acquisition/reception of the protected content stream  121 , etc.). 
         [0116]      FIG. 2B  details an alternative functioning of the receiving device  12  and the second device  13  while processing the protected content  121  and the complementary stream  122  generated as described by  FIGS. 1A and 1B . The difference between this structure and the one presented in  FIG. 2A  is that the same mark generator  5  generates both marks: the first mark  511  and the second mark  512 . 
         [0117]    According to one aspect, complementary stream  122  is transmitted from receiving device  12  to the second device  13  using the mark generator  5 . In this situation, the mark generator  51  is a SIM card, secure USB device or any other secure hardware/software component capable to securely read/write/store binary data. 
         [0118]    According to one aspect, the mark generator  5  comprises means of authentifying the receiving device  12  and/or the second device  13  to guarantee a secure transmission of the complementary stream  122  from receiving device  12  to the second device  13 . 
         [0119]      FIG. 2C  details an alternative functioning of the receiving device  12  and the second device  13  while processing the protected content  121  and the complementary stream  122  generated as described by  FIGS. 1A and 1B . The difference between this structure and the ones presented in  FIGS. 2A and 2C  is that the complementary stream  122  or the complementary marked stream  123  is transmitted form a remote server  7  to the second device  13 . 
         [0120]    The complementary marked stream  123  is generated from the complementary stream  122  and the second mark  152  and it comprises the information needed to generate the second marked stream  127  from the protected content stream  121 . The generation of complementary marked stream  123  will be described later ( FIG. 3C ). 
         [0121]    According to one aspect, the complementary marked stream  123  is generated as described in WO 2008/081113, the subject matter of which is incorporated herein by reference. 
         [0122]    According to one aspect, both second device  13  and remote server  7  comprise well known cryptographic means to guarantee the secure transmission of the complementary stream  122  from remote server  7  to the second device  13 . 
         [0123]    According to another aspect, the mark generator  5  or  51  participates into the process of protection of the transmission of the complementary stream  122  or the complementary marked stream  123  from remote server  7  to the second device  13 . The roles played in this process are: securely store the information used by the authentication process (e.g., SIM card ID) between the second device  13  and the remote server  7  and/or to encrypt/decrypt messages exchanged between the second device  13  and the remote server  7 . 
         [0124]      FIG. 3A  highlights the different steps that the descrambling device  21  performs to generate a marked content  124  or  127  from the protected content stream  121  and the complementary stream  122  in function of the first mark  511  or the second mark  512 . 
         [0125]    The descrambling device  21  performs the following steps:
       descrambling  211  the protected content stream  121  using the information contained in the complementary stream  122  by generating a clear content stream  125  with similar visual and audible representation as the original content  1 ;   marking  311  the clear content stream  125  by generating a marked content  124  or  127  in function of the first mark  511 , respectively the second mark  512 .       
 
         [0128]    According to one aspect, the descrambling step  211  uses decryption keys contained in the complementary stream  122  to decrypt protected content stream  121  to the clear content stream  125 , where the decryption algorithms are the ones well-known by the skilled man. 
         [0129]    According to another aspect, the descrambling step  211  uses the original parts of the original content stream  1  contained in the complementary stream  122  to insert it back into the protected content stream  121  to obtain the clear content stream  125 . 
         [0130]    According to another aspect, the insertion of the original parts back into the protected content stream  121  replaces the dummy ones inserted by the scrambling module  2 . 
         [0131]    According to one aspect, the marking step  311  of the clear content stream  125  uses information comprised in the complementary stream  122 . 
         [0132]    According to one aspect, the marking step  311  of the clear content stream  125  is done over an encoded or decoded form of the clear content stream  125  using marking technologies well-known by the skilled man. 
         [0133]    According to another aspect, the marking step  311  of the clear content stream  125  is done as described in WO &#39;241. 
         [0134]      FIG. 3B  highlights the different steps that an alternative descrambling device  21  performs to generate a marked content  124  or  127  from the protected content stream  121  and the complementary stream  122  in function of the first mark  511  or the second mark  512 . 
         [0135]    The descrambling device  21  performs the following steps:
       marking  312  the complementary stream  122  using the first mark  511  or the second mark  512  by generating a marked complementary stream  126 ;   descrambling  212  the protected content stream  121  using the information contained in the marked complementary stream  126  by generating a marked content  124  or  127 .       
 
         [0138]    According to one aspect, the marked complementary stream  126  is generated during the marking step  312  as described in WO &#39;113. 
         [0139]    According to another aspect, the complementary stream  122  contains the original parts form the original content stream  1  extracted by the scrambling module  2  and replaced with dummy data in the protected content stream  121 , as described for example in WO 2005/032135, the subject matter of which is incorporated herein by reference. The complementary stream  122  contains the data from the marking metadata stream  132 , as disclosed in  FIG. 1B . The marking metadata stream  132  is generated as described in WO &#39;241. The marking step  312  generates a marked complementary stream  126  as following:
       some marked parts of the marking metadata stream  132  are chosen to be inserted into the audiovisual content in function of the first mark  511  or the second mark  512 , as described in WO &#39;241;   the marked complementary stream  126  is generated by mixing together the chosen marked parts from the marking metadata stream  132  with the original parts of the original content stream  1  comprised in the complementary stream  122 .       
 
         [0142]    The format of the marked complementary stream  126  is the format of the marking metadata stream  132 , the format of the complementary stream  122  or any other format, proprietary or standard. 
         [0143]    The descrambling step  212  generates the mark content stream  124  or  127  by inserting the all content parts comprised in the marked complementary stream  126  (marked and original) into the protected content stream  121 . This step can be implemented for example like in WO &#39;113. 
         [0144]      FIG. 3C  highlights the different steps that an alternative descrambling device  21  performs to generate a marked content  127  from the protected content stream  121  in function of the second mark  512 . The difference between this embodiment and the one presented in  FIG. 3B  is that only the descrambling step  212  is executed by the descrambling module  21  on the second device  13 , while the marking step  312  is applied remotely by a remote server  7 . In this case, only the marked complementary stream  126  is transmitted between from the remote server  7  to the second device  13 .