Patent Publication Number: US-2007098170-A1

Title: Digital broadcasting conditional access system and method using authorization revocation list

Description:
FIELD OF THE INVENTION  
      The present invention relates to a digital broadcasting conditional access system and method using an Authorization Revocation List (ARL); and more particularly, to a digital broadcasting conditional access system and method using an ARL for preventing an illegal pay broadcasting viewing after a secession time by promptly revoking an entitlement of pay service seceders through a periodical transmission of ARL that is daily or monthly prepared and updated to subscribers.  
     DESCRIPTION OF RELATED ART  
      In digital broadcasting conditional access system, subscribers may freely join in and secede from or leave pay broadcasting services. This digital broadcasting conditional access system transmits an entitlement key to a subscriber upon joining or cancels the key upon secession whenever there is a joining for pay services or secession therefrom. The entitlement key refers to an Authorization Key (AK) in case of a 3-layer key model shown in  FIG. 1  and a Receiving Group Key (RGK) in case of a 4-layer key model in  FIG. 2 .  
      A common pay service joining procedure for subscribers is relatively simpler than a seceding procedure as follows.  
      First, a subscriber who wants to join in a service gives an application for a desired service to a head-end conditional access system on-line or off-line. Then, the head-end conditional access system authenticates a validation of the subscriber.  
      If the authentication result shows that the application is from the valid subscriber, the head-end conditional access system updates the applied contents of pay service and then sends an entitlement key required for viewing to the subscriber. As mentioned above, the entitlement key may be an AK in case of 3-layer key transmission model shown in  FIG. 1  and an RGK in case of 4-layer key transmission model in  FIG. 2 . Meanwhile, if the subscriber who applied for the pay service doesn&#39;t have the required entitlement key, the head-end conditional access system creates a new key and then sends it to the subscriber. Then, the subscriber receives the new key sent from the head-end conditional access system and again makes an application for the pay service.  
      On the other hand, the pay service seceding procedure is carried out as below.  
      First of all, a subscriber gives an application for secession of a specific pay service to the head-end conditional access system on-line or off-line. Then, the head-end conditional access system authenticates a validation for the secession application of the subscriber. If the authentication result shows that there is no problem with the secession application of the subscriber, the head-end conditional access system transmits entitlement keys to only subscribers excluding the subscriber who made the secession application upon a next entitlement key updating.  
      In this conventional seceding method, however, the subscriber who has already made the secession application can continue to view the pay broadcasting from the secession time to the update time of the entitlement key. Moreover, there is no idea or method to prevent such an illegal viewing.  
      For example, if a subscriber makes an application for secession at 00:01 and an entitlement key is updated at 24:00, the subscriber is illegally allowed to view pay broadcasting for 23 hours and 59 minutes for which he/she has no entitlement to view such pay broadcasting. That is, if the update period is 24 hours, it is possible to do the illegal viewing for a maximum 24 hours.  
     SUMMARY OF THE INVENTION  
      It is, therefore, a primary object of the present invention to provide a digital broadcasting conditional access system and method using an ARL for preventing an illegal pay broadcasting viewing after a secession time by promptly revoking an entitlement of pay service seceders through a periodical transmission of ARL that is daily or monthly prepared and updated to subscribers.  
      In accordance with one aspect of the present invention, there is provided a digital broadcasting conditional access system using Authorization Revocation List (ARL) for transmitting service secession information to a receiving end or host for conditional access of broadcasting services, comprising: an ARL providing means for creating daily and monthly ARLs separately and updating the ARLs based on the service secession information of subscribers; a Subscriber Management System (SMS) means for receiving service secession requests from subscribers and delivering the requests to the ARL providing means; a Subscriber Authorization System (SAS) means for producing an Entitlement Control Message (ECM) and an Entitlement Management Message (EMM) for subscriber authorization at the receiving end by using the daily and the monthly ARLs managed by the ARL providing means; and a transmitting means for periodically transmitting the ECM to subscribers via an in-band channel and the EMM via an out-of-band channel.  
      In accordance with another aspect of the present invention, there is provided a service conditional access method using an ARL in a head-end or sending unit of a digital broadcasting conditional access system, comprising the steps of: (a) creating and disusing a daily ARL, and updating the ARL today  whenever there is a request for subscriber secession; (b) generating and disusing a monthly ARL, and updating the monthly ARL last  by day unit when there is a request for subscriber secession; (c) periodically inserting the daily ARL today  into an ECM and transmitting the inserted message to subscribers; and (d) periodically inserting the monthly ARL last  into an ECM and transmitting the inserted message to subscribers.  
      In accordance with still another aspect of the present invention, there is provided a service conditional access method using an ARL in a host or subscriber receiving unit of a digital broadcasting conditional access system, comprising the steps of: (a) receiving an ECM or EMM periodically transmitted form a head-end; (b) extracting an ARL from the received ECM or EMM; (c) interpreting the extracted ARL to confirm whether or not service secession information has corresponding subscriber information of the host; (d) if the confirmation result at said step (c) shows that there is the corresponding subscriber information of the host, deleting an entitlement key of the corresponding subscriber; and (e) if the confirmation result at said step (c) shows that there is no corresponding subscriber information of the host, allowing the reception of broadcasting.  
      The other objectives and advantages of the invention will be understood by the following description and will also be appreciated by the embodiments of the invention more clearly. Further, the objectives and advantages of the invention will readily be seen that they can be realized by the means and its combination specified in the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects and features of the instant invention will become apparent from the following description of preferred embodiments taken in conjunction with the accompanying drawings, in which:  
       FIG. 1  is a block diagram showing a configuration of a 3-layer key transmission model of a common digital broadcasting conditional access system;  
       FIG. 2  is a block diagram showing a configuration of a 4-layer key transmission model of a common digital broadcasting conditional access system;  
       FIG. 3  is a block diagram showing a configuration of a head-end of a digital broadcasting conditional access system using an ARL in accordance with an embodiment of the invention;  
       FIGS. 4   a  and  4   b  are diagrams showing structures of an ECM ARL  and an EMM ARL  in accordance with an embodiment of the invention, respectively;  
       FIG. 5  is a diagram for describing a method of inserting an ARL today  into the ECM ARL  in accordance with an embodiment of the invention; and  
       FIG. 6  is a flowchart illustrating a service conditional access method using the ARL in a subscriber reception unit or host in accordance with an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The above-mentioned objectives, features, and advantages will be more apparent by the following detailed description associated with the accompanying drawings; and based on this, the invention will be readily conceived by those skilled in the art to which the invention pertains. Further, in the following description, well-known arts will not be described in detail if it seems that they could obscure the invention in unnecessary detail. Hereinafter, a preferred embodiment of the present invention will be set forth in detail with reference to the accompanying drawings.  
      The present invention makes use of an “ARL” with available period of one month as a basic charge term. The ARL contains secession information of subscribers who made applications for secession for specific pay broadcasting services, and is updated whenever subscribers give applications for secession to a head-end or sending system. This ARL is delivered to subscribers through an Entitlement Control Message (ECM) and an Entitlement Management Message (EMM).  
      The ARL today  delivered through the ECM contains information of subscribers who made applications for secession with respect to pay broadcasting services from 00:00 to 24:00. And, the ARL last  delivered through the EMM includes information of subscribers who made applications for secession with respect to pay broadcasting services from the first day of a specific month to a day just before a day of delivering the ARL today  through the ECM. For example, if today is August 17, the ARL today  is sent to subscribers through the ECM having secession information occurred from 00:00 August 17 to a transmission time thereof while ARL last  is transmitted to subscribers through the EMM having secession information taken place from 00:00 August 1 to 24:00 August 16.  
      In general, the ECM is repeatedly sent from the head-end to subscribers with very short period, e.g., 0.1 sec. Since the subscribers cannot view pay broadcasting without receipt of such ECM, they must receive such ECM. That is, if the head-end transmits the ARL today  through the ECM, the subscribers can receive the ARL today  with high reliability through the ECM that is very frequently transmitted.  
      However, if a size of the ARL is large, there is a possibility that its transmission through the ECM consumes a large channel bandwidth. Therefore, the present invention transmits only the ARL today  that is created during late one day on the basis of the current time, i.e., a transmission time of ARL. In addition, the ARL last  that is created from the first day of that month to just the day before on the basis of the current time is sent through the EMM. The reason the previous ARL is continuously maintained during one month as above is for subscribers to ready for an instance where there is a failure to receive the ECM. Namely, although subscribers who made secession applications didn&#39;t receive the ECM for one day after the secession application, those subscribers are divested of entitlement of pay broadcast viewing if they receive the EMM until the end of that month. At this time, the transmission period of the EMM may be properly varied by the system operator based on the channel bandwidth.  
      A Conditional Access Module (CAM) of subscriber who received the ARL confirms whether or not its own subscriber information is involved in the secession information contained therein and deletes an entitlement key of the subscriber if any.  
      For example, if a subscriber makes an application for secession for pay broadcasting service, he/she immediately receives the ARL including his/her own secession information through the ECM. Then, a conditional access application in the CAM of the subscriber interprets the ARL and confirms the fact that his/her secession information is involved therein. Lastly, the conditional access application deletes an entitlement key corresponding to the secession information of the subscriber in the ARL from a memory within the CAM.  
      Although the subscriber who applied for the secession rejects the receipt of the ECM in any manner, he/she cannot view pay broadcasting without receipt of such ECM and thus cannot do illegal broadcasting viewing. Further, although the subscriber tries to view pay broadcasting on the next day after avoiding viewing for the day of making the secession application, he/she would receive the ARL that is periodically updated through the EMM, thereby allowing no illegal pay broadcasting viewing.  
       FIG. 1  is a block diagram showing a configuration of a 3-layer key transmission model of a common digital broadcasting conditional access system and  FIG. 2  is a block diagram showing a configuration of a 4-layer key transmission model of a common digital broadcasting conditional access system.  
      First of all, there will be described a 3-layer key transmission model referring to  FIG. 1 .  
      In the 3-layer key transmission model, a head-end  100  as a sending unit includes a scrambler  101  and two encryptors  102  and  103 ; and a host  110  as a subscriber reception unit includes a descrambler  111  and two decryptors  112  and  113 .  
      An Audio/Video (AV) source  1001  is encrypted by the scrambler  101  of the head-end  100 . At this time, a Control Word (CW) is used as an encryption key.  
      The source  1011  so encrypted and sent is decrypted by the descrambler  111  of the host  110  to provide an original source  1024 . Also, a CW is used as an encryption key for the decryption.  
      The head-end  100  must encrypt a CW  1002  and then send it to the host  110  so that the descrambler  111  can decrypt the scrambled source  1011  using a CW  1021 . At this time, a message used in sending an encrypted CW  1013  is an ECM  1012 .  
      The decryptor  112  of the host  110  decrypts the ECM  1012  by using an Authorization Key (AK)  1022  indicating a decryption key to obtain the CW  1021 .  
      Since the CW  1002  in the head-end  100  is encrypted by an AK  1003 , the head-end  100  must encrypt the AK  1003  and then send it to the host  110 . Specifically, the head-end  100  encrypts the AK  1003  with a Multiple Public Key (MPK)  1004 ; and the encrypted AK  1015  is fed to the host  110  through an EMM message  1014 .  
      In the host  110 , the AK  1022  is derived by decrypting the received EMM message  1014  with the MPK  1023 . As described above, the AK  1022  is used in decrypting the encrypted CW  1013 . In this 3-layer key transmission model, the keys serving as an “entitlement key” are the AKs  1003  and  1022 .  
      Meanwhile, in the 4-layer key transmission model shown in  FIG. 2 , one encryptor and one decryptor are further provided in a head-end  200  and a host  210 , respectively, compared to the 3-layer key transmission model of  FIG. 1 .  
      In the 4-layer key transmission model, only following process is different from the process of the 3-layer key transmission model. That is, the head-end  200  encrypts an AK  1003  by using an RGK  2001  and then the RGK  2001  with an MPK  1004 . And the host  210  decrypts an RGK  2021  by using an MPK  1023  and then an AK  1022  with the decrypted RGK  2021 .  
      In this 4-layer key transmission model, the keys serving as an “entitlement key” are the RGKs  2001  and  2021 .  
       FIG. 3  is a block diagram showing a configuration of a head-end of a digital broadcasting conditional access system using an ARL in accordance with an embodiment of the invention.  
      As shown therein, a head-end conditional access system, that is, the head-end of the digital broadcasting conditional access system comprises an ARL providing server  301 , a Subscriber Management System (SMS)  302 , a Subscriber Authorization System (SAS), and a transmitting unit  300 . And, the transmitting unit  300  includes multiplexers  304  and  305 , scramblers  306  and  307 , in-band modulators  308  and  309 , and an Out-Of-Band (OOB) modem  310 .  
      First, each of the components in the head-end will be explained in detail hereinafter. The ARL providing server  301  separately creates daily and monthly ARLs and updates them based on service secession information. More specifically, the ARL providing server  301  performs the following two functions. Firstly, it creates and disuses a daily ARL, and updates the daily ARL today  whenever there is secession request of subscribers. Secondly, it generates and disuses a monthly ARL, and updates the monthly ARL last  by day unit upon a secession request of subscribers.  
      In the meantime, the SMS  302  receives a secession request for services from subscribers and sends it to the ARL providing server  301 . And the SAS  303  produces an ECM and an EMM for subscriber authorization at a receiving end based on the daily ARL and the monthly ARL managed by the ARL providing server  301 .  
      Then, the transmitting unit  300  transmits the ECM to subscribers over an in-band channel at a preset period of, e.g., 0.1 sec and the EMM to subscribers over an out-of-band channel at a preset period of, e.g., one day.  
      Hereinafter, a service conditional access method carried out in the head-end device using ARLs will be described, together with the head-end device.  
      The ARL providing server  301  serves to create or disuse an ARL. The ARL is newly created by the ARL providing server  301  in the first day of a month and reused in the end day of that month.  
      When a subscriber requests the SMS  302  of the head-end to secede pay services on-line or off-line, it causes the ARL providing server  301  to know the fact and then adds information of the subscriber who made the secession request to the ARL.  
      Next, the ARL providing server  301  delivers the newly updated ARL to the SAS  303 . At this time, the ARL delivered is classified into a daily ARL today    3001  and a monthly ARL last    3001  depending on the generation time of the ARL. The daily ARL today    3001  contains an ARL created after 00:00 this day on the basis of the current time; and the monthly ARL last    3001  contains ARL created from the first day of this month to midnight yesterday on the basis of the current time.  
      Thereafter, the SAS  303  produces an ECM ARL    3011  with the ARL today    3001  and an EMM ARL  with the ARL last    3001 , out of the ARL  3001 . At this time, the ECMs ARL    3011  are produced by the number of physical channels supported by the head-end. For example, if the head-end supports  100  physical channels, the SAS  303  should produce  100  number of ECMs ARL    3011 , each of which has an ARL of each channel.  
      An example of producing a different ARL every physical channel is as follows. First, it is assumed that physical channels a subscriber # 1  joined are CH 1 , CH 3  and CH 5 , and physical channels a subscriber # 2  joined are CH 2 , CH 3  and CH 6 . And it is assumed that the two subscribers have all seceded from all the joined channels. In this case, the subscriber # 1  is involved in the ARL of ECM ARL  corresponding to the physical channel CH 1 . And the subscribers # 1  and # 2  are involved in the ARL of ECM ARL  corresponding to the physical channel CH 3 . Lastly, the subscribers # 1  and # 2  are included in the ARL of ECM ARL  corresponding to the physical channels CH 5  and CH 6 . If there are more than  2  virtual channels with respect to one physical channel, the SAS  303  sorts out and then sends secession subscribers for each virtual channel through the ECM ARL , as shown in  FIG. 4   a.    
      The ECMs ARL  produced by the number of physical channels are sequentially passed through multiplexers (MUXS)  304 , scramblers  306  and  307 , and in-band modulators  308  and  309  that are prepared for each channel, and then lastly sent to the host via in-band channels. At this time, the ECMs ARL    3011  and  3012  contain the ARL today  encrypted with the AK  1003  shown in  FIG. 1 .  
      The NUXs  304  and  305  multiplex the ECMs ARL    3011  and  3012  from the SAS  303  and audio/video sources  3021  and  3022 ; and the scramblers  306  and  307  encrypt the multiplexed ECM ARL  with the CWs  3031  and  3032  and the audio/video source. The in-band modulators  308  and  309  modulate the encrypted ECM ARL  and the audio/video source.  
      The SAS  303  sends to subscribers the ARL created from the first day of this month to yesterday on the basis of the current time through the EMM ARL    3041 , excluding the ARL created this day provided through the ECMs ARL    3011  and  3012 . At this time, the EMM ARL    3041  is sent to the host via the OOB modem  310 .  
      The ARL last  of EMM ARL  in the SAS  303  is encrypted with different keys depending on the 3-layer key transmission structure or model or the 4-layer key transmission structure or model. In the 3-layer key transmission structure, the ARL last  in EMM ARL  is encrypted through the MPK  1004  as shown in  FIG. 1 , indicating a unique encryption key every subscriber. Therefore, the SAS  303  must create and send the EMMs ARL  by the number of subscribers in case of using the 3-layer key transmission structure.  
      On the other hand, in the 4-layer transmission structure, the ARL last  in EMM ARL  is encrypted with an RGK  2001  indicating a group key of a service group each subscriber joined. Therefore, the SAS  303  must create and send the EMMs ARL  by the number of groups in case of using the 4-layer transmission structure.  
       FIGS. 4   a  and  4   b  are diagrams showing structures of the ECM ARL  and the EMM ARL  in accordance with an embodiment of the invention, respectively.  
      First, an explanation of each field constituting the ECM ARL  as shown in  FIG. 4   a  will be given as below.  
      The ECM ARL  massage is composed of a sequence number field  401 , a number of Control Words (CW) pair blocks field  402 , and N CW pair fields  403  to  405 .  
      Specifically, the sequence number field  401  is configured to confirm the sequence of messages inputted to the CAM used in the host  110  or  210  of  FIG. 1  or  2 . If the ECM ARL  with same sequence number or previous sequence number is inputted, the CAM doesn&#39;t take this.  
      The number of CW pair blocks field  402  denotes the number of the CW pair blocks  403 ,  404  and  405  corresponding to the number of virtual channels that can be processed by one ECM ARL . If the number of virtual channels that can be processed by one ECM ARL  is  4 , the number of CW pair blocks  402  becomes  4  and thus has 4 control words pair blocks  403 ,  404 ,  405 .  
      The CW pair blocks fields  403 ,  404  and  405  include ARL today    3001  encrypted with the AK, in addition to a channel ID, an odd/even selection flag, and an odd/even CW basically contained in the ECM. To organize the ECM ARL  so, the SAS  303  sorts out the ARL today  provided from the ARL providing server  301  by each channel ID of virtual channel and then inserts them into corresponding CW pair blocks  403 ,  404  and  405 . Namely, each of the CW pair blocks  403 ,  404  and  405  contains secession subscriber information sorted out by each virtual channel.  
      Next, an explanation of each field constituting the EMM ARL  message shown in  FIG. 4   b  will be provided as follows.  
      The EMM ARL  message is composed of a sequence number field  411 , a group ID field  412 , and an ARL last  list field  413 .  
      Specifically, the sequence field  411  is the same as the field  401  of  FIG. 4   a.  And the group ID field  412  is valid only when the head-end conditional access system makes use of the 4-layer key transmission structure and represents an ID value for subscriber group corresponding to the ARL last  contained in the EMM ARL .  
      The ARL last  list field  413  includes the entire list of the ARL last  in case of the 3-lay key transmission structure; and is encrypted with the MPK  1004  and sent to each subscriber. Meanwhile, the ARL last  list field  413  includes only ARL corresponding to a group that the group ID indicates out of the entire list of the ARL last  in case of the 4-lay key transmission structure. This field is encrypted with the RGK  2001  and then sent to each subscriber group.  
       FIG. 5  is a diagram for describing a method of inserting the ARL today  into the ECM ARL  in accordance with an embodiment of the invention.  
      The invention inserts each record of the ARL today  into the ECM ARL  by using a carousel scheme, as shown in  FIG. 5 . Using this scheme, the ARL today  can be effectively inserted into the ECM ARL  although the size of ARL today  is larger or less than the ECM ARL  with fixed size.  
      First, if the number of records of the daily ARL today  is less than the number of records that can be processed by one ECM, all record information of the daily ARL today  is inserted into one ECM for transmission. For example, it is assumed that a record #M  507  value of an ARL today    500  is “6” and one ECM ARL    521 ,  522  or  523  can process by 6 records at a time. In this case, each of the ECM ARL    521 ,  522  and  523  sent to the host includes all the records, i.e., 6 records of the ARL today    501 .  
      On the other hand, if the number of records of the daily ARL today  exceeds the number of records that can be processed by one ECM, each of all record information of the daily ARL today  is sequentially inserted into plural ECMs transmitted in order until all the record information of the daily ARL today  is inserted.  
      For instance, it is assumed that the record #M  507  value is “12” and one ECM ARL    521 ,  522  or  523  can process by 6 records at a time. In such a case, the first ECM ARL    521  sent to the host includes first to sixth records of the ARL today    500  and the second ECM ARL    522  includes seventh to twelfth records of ARL today    500 . Thereafter, if there is no additional record in the ARL today    500 , the third ECM ARL    523  again includes first to sixth records of the ARL today    500 . If the second ECM ARL    522  is sent with the seventh to twelfth records of the ARL today    500  and then the thirteenth record is added to the ARL today    500 , the third ECM ARL    523  is sent with 6 of the thirteenth to fifth records of the ARL today    500 . This process is recursively performed as shown in  FIG. 5 .  
       FIG. 6  is a flowchart illustrating a service conditional access method using the ARL in the subscriber reception unit or the host in accordance with an embodiment of the invention. This is already described above; and therefore, a schematic description thereof will be given below referring to  FIG. 6 .  
      At a first step S 600 , the host receives an ECM or EMM periodically transmitted from the head-end, as shown in  FIG. 3 . And then, it extracts an ARL from the received ECM or EMM at step S 602 . A daily ARL is extracted from the ECM, while a monthly ARL is extracted from the EMM, wherein each of them is the same as already explained early.  
      Next, the host interprets the extracted ARL at step  604 , and confirms whether subscriber information on the user of the host is involved in service secession information acquired by the interpretation at step S 606 .  
      If the confirmation result shows that there is the subscriber information, the host deletes an entitlement key of the subscriber at step S 608 ; and if the confirmation result shows that there is no subscriber information, the host is allowed to receive broadcasting at step S 610 . At this time, if the subscriber doesn&#39;t receive the entitlement key validly updated, of course, the host is not allowed to receive the broadcasting. The above entitlement key deleting process is made by deleting the entitlement key of the subscriber stored in the CAM.  
      As described above, the present invention can effectively update an entitlement key when a subscriber makes an application for pay service secession in a digital broadcasting conditional access system. In other words, the invention can prevent an illegal pay broadcasting viewing by promptly revoking an entitlement of a subscriber who made an application for pay service secession by using an ARL.  
      In general, since an ECM not only has a very short transmission period of, e.g., 01 sec but also subscribers are not fundamentally allowed to receive pay broadcasting services without receipt of an ECM, the transmission of an ARL using such ECM is very effective. Accordingly, the invention transmits an ARL created during late one day on the basis of the current time through an ECM to subscribers out of ARLs, thereby allowing no broadcasting reception for seceders by promptly revoking an entitlement of pay service seceders.  
      Moreover, the invention transmits an ARL generated from the first day of this month to just the day before on the basis of the current time through an EMM, and therefore, can considerably reduce system load caused by increase of such ARL.  
      The method of the present invention as mentioned above may be implemented by a software program and stored in a computer-readable storage medium such as CD-ROM, RAM, ROM, floppy disk, hard disk, optical magnetic disk, etc. This process may be readily carried out by those skilled in the art; and therefore, details of thereof are omitted here.  
      The present application contains subject matter related to Korean patent application No. 2005-0104877, filed with the Korean Intellectual Property Office on Nov. 03, 2005, the entire contents of which are incorporated herein by reference.  
      While the present invention has been described with respect to the particular embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.