Abstract:
A system and method for storing and retrieving program material for subsequent replay is disclosed. The method comprises the steps of receiving access control information and the program material encrypted according to a first encryption key, the access control information including the first encryption key and control data; further encrypting the access control information and the encrypted program material according to a second encryption key; encrypting the second encryption key according to a third encryption key to produce a fourth encryption key; and storing the encrypted access control information and encrypted program material and the fourth encryption key.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is related to the following patent applications, all of which applications are hereby incorporated by reference herein: 
   U.S. patent application Ser. No. 09/620,833, entitled “SECURE STORAGE AND REPLAY OF MEDIA PROGRAMS USING A HARD-PAIRED RECEIVER AND STORAGE DEVICE,” by Raynold M. Kahn, Gregory J. Gagnon, David D. Ha, Peter M. Klauss, Christopher P. Curren, and Thomas H. James, filed on same date herewith; 
   U.S. patent application Ser. No. 09/621,476, entitled “SUPER ENCRYPTED STORAGE AND RETRIEVAL OF MEDIA PROGRAMS IN A HARD-PAIRED RECEIVER AND STORAGE DEVICE,” by Raynold M. Kahn, Gregory J. Gagnon, David D. Ha, Peter M. Klauss, Christopher P. Curren, and Thomas H. filed on same date herewith; 
   U.S. patent application Ser. No. 09/620,773, entitled “SUPER ENCRYPTED STORAGE AND RETRIEVAL OF MEDIA PROGRAMS WITH MODIFIED CONDITIONAL ACCESS FUNCTIONALITY, “by Raynold M. Kahn, Gregory J. Gagnon, David D. Ha, Peter M. Klauss, Christopher P. Curren, and Thomas H. James, filed on same date herewith; 
   U.S. patent application Ser. No. 09/620,772, entitled “SUPER ENCRYPTED STORAGE AND RETRIEVAL OF MEDIA PROGRAMS WITH SMARTCARD GENERATED KEYS,” by Raynold M. Kahn, Gregory J. Gagnon, David D. Ha, Peter M. Klauss, Christopher P. Curren, and Thomas H. James, filed on same date herewith; and 
   U.S. patent application Ser. No. 09/491,959, entitled “VIRTUAL VIDEO ON DEMAND USING MULTIPLE ENCRYPTED VIDEO SEGMENTS,” by Robert G. Arsenault and Leon J. Stanger, filed on Jan. 26, 2000. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to systems and methods for providing video program material to subscribers, and in particular to a method and system for securely storing and replaying media programs. 
   2. Description of the Related Art 
   In recent years, there has been increasing interest in allowing cable and satellite television subscribers to record broadcast media programs for later viewing. This capability, hereinafter referred to as personal video recording (PVR), can be used to provide video-on-demand (VOD) services, or simply to allow the subscriber to save media programs for repeated viewing and/or archival purposes. 
   In the past, video cassette tape recorders (VCRs) have been used for such personal video recording. Recently, however, hard disks, similar to those used in personal computers, have been used to store media programs for later viewing. Unlike VCRs, such devices typically do not include a tuner, and are instead coupled to the satellite receiver or cable box. Also unlike VCRs, these devices are typically used to record digitized content, not analog video. This difference is both advantageous and disadvantageous. 
   An advantage of such devices is that they permit long term storage and multiple replays without substantial degradation. Another advantage is that they permit more rapid trick-play functions such as fast forwarding and rewinding. A disadvantage of such devices is that they are capable of making multiple-generation copies of the program material as well, and without serious degradation. This raises the very real possibility that the multiple generation copies of the media programs will be produced and distributed without permission. This possibility has caused some media providers to be reluctant to allow their media programs to be recorded by such devices. 
   To ameliorate this problem, it is critical to protect the stored media programs with strong security and copy control. Current devices do not scramble media programs before storage, nor do they store copy protection information. Instead, such devices record decrypted program content into the storage disk using a paired hardware scheme in which the hard disk controller and hard disk are paired to each other specifically through a specific interface. Because the hard disk controller and the disk itself are essentially paired together, storage or playback will not function if the disk were to be removed and transferred to another player. The weakness of this security scheme is that it relies only on the paired hardware to ensure security . . . the media programs stored on the disk drive itself are not encrypted. 
   While it would presumably be possible to simply store the datastream as it is received from the broadcaster for later replay, this technique has distinct disadvantages. One such disadvantage is that it would provide pirates a permanently recorded version of the encrypted datastream, thus providing the pirate with information that can be used to perform detailed analyses of the datastream itself to determine the encryption techniques and codes. 
   What is needed is a system and method for securely recording broadcast media programs (including impulse purchase pay-per-view programs) for limited use playback at a later time. Such a system could be used to support video-on-demand (VOD), thus allowing the subscriber to purchase media programs and games from the set top box instantly without worrying about the start time of the program. What is also needed is a system and method that does not require substantial changes to subscriber hardware, such as the conditional access module (CAM) that is used to provide the key to decrypt the media programs for presentation to the subscribers. 
   SUMMARY OF THE INVENTION 
   In summary, the present invention describes a system and method for storing and retrieving program material for subsequent replay. The method comprises the steps of receiving access control information and the program material encrypted according to a first encryption key, the access control information including the first encryption key and control data; further encrypting the access control information and the encrypted program material according to a second encryption key; encrypting the second encryption key according to a third encryption key to produce a fourth encryption key; and storing the encrypted access control information and encrypted program material and the fourth encryption key. 
   The apparatus comprises a tuner, for receiving encrypted access control information and the program material encrypted according to a first encryption key, the access control information including the first encryption key and control data; a first encryption module, communicatively coupled to the tuner and communicatively coupleable to a data storage device, the first encryption module for further encrypting the encrypted program material and the access control information according to a second encryption key; a second encryption module, communicatively coupled to the first encryption module and communicatively coupleable to the data storage device, the second encryption module for encrypting the second encryption key according to a third encryption key to produce a fourth encryption key; a first decryption module, communicatively coupleable to the disk drive, for decrypting the fourth encryption key to produce the second encryption key; a second decryption module, communicatively coupled to the first decryption module and the tuner and communicatively coupleable to the data storage device, for decrypting the further encrypted program material to produce the encrypted program material and the encrypted access control information using the second encryption key; a conditional access module, communicatively coupleable to the second decryption module and the tuner, for selectably accepting the access control information selected from the group comprising the access control information received in the tuner and the access control information decrypted by the second decryption module, the conditional access module comprising a third decryption module for decrypting the encrypted access control information to produce the first encryption key; and a fourth decryption module for decrypting the encrypted program material to produce unencrypted program material using the first encryption key. 
   One object of the present invention is to provide for the reception and decryption of broadcast media programs, including impulse pay-per-view (IPPV) programs, that can be played and recorded onto storage media and allows playback at a later time with limited use. The data itself may be placed in short term storage, but the replay of the media programs can be accomplished with trick play functions such as forward, reverse, fast forward, fast reverse, frame advance, and pause functions. 
   Another object of the present invention is to provide PVR functions which provide recording, delayed playback, and trick play of IPPV media programs from the storage media without requiring a pre-purchase of the IPPV media program. This would allow the IPPV media program to be purchased and viewed at the users leisure without requiring the IPPV media program to be purchased prior to storage. Ideally, such a system would allow the user to select the IPPV media program from the storage device, subject to limited play rights. 
   Still another object of the present invention is to provide a pairing between the storage media and elements of the subscriber&#39;s IRD to assure that playback of the media programs from the storage device are permitted only with the proper IRD. 
   Still another object of the present invention is to provide a secure means for storing broadcast data streams (including IPPV and games) on a data storage device, while providing for adequate copy protection. 
   Still another object of the present invention is to provide a system and method for handling the archiving and retrieving of media programs and other data, even if the data storage device fails. 
   Still another object of the present invention is to provide a system and method that allows media program purchases to be recorded in a way that is analogous to that which is employed for real-time off-the-air programs. 
   Still another object of the present invention is to provide a system that provides a growth path to a system permitting IPPV media programs to be previewed without charge for an initial period of time with the option to purchase the media program or cancel the purchase, regardless of whether the program is retrieved from the storage device or obtained from a real time broadcast. 
   Still another object of the present invention is to achieve all of the foregoing without requiring substantial changes to conditional access module hardware and/or software. 
   The present invention eliminates concerns regarding the proliferation of unauthorized digital copies of the media programs by use of a strong encryption method. Further, the present invention ensures that the stored material cannot be distributed since such decryption of the material can only be successfully performed by the encrypting IRD. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings in which like reference numbers represent corresponding parts throughout: 
       FIG. 1  is a diagram showing an overview of a video distribution system; 
       FIG. 2  is a block diagram showing a typical uplink configuration showing how video program material is uplinked to a satellite for transmission to subscribers using a single transponder; 
       FIG. 3A  is a diagram of a representative data stream received from a satellite; 
       FIG. 3B  is a diagram illustrating the structure of a data packet; 
       FIG. 4  is a block diagram illustrating a high-level block diagram of the IRD; and 
       FIGS. 5A-5C  are diagrams illustrating the storage and retrieval of data from a media storage device. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   In the following description, reference is made to the accompanying drawings which form a part hereof, and which show, by way of illustration, several embodiments of the present invention. It is understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
   Video Distribution System 
     FIG. 1  is a diagram illustrating an overview of a video distribution system  100 . The video distribution system  100  comprises a control center  102  in communication with an uplink center  104  via a ground or other link  114  and an integrated receiver/decoder (IRD)  132  at receiver station  130  via a public switched telephone network (PSTN) or other link  120 . The control center  102  provides program material to the uplink center  104 , coordinates with the receiver station  130  to offer subscribers  110  pay-per-view (PPV) program services, including billing and associated decryption of video programs. 
   The uplink center  104  receives program material and program control information from the control center  102 , and using an uplink antenna  106 , transmits the program material and program control information to the satellite  108  via uplink  116 . The satellite  108  receives and processes this information, and transmits the video programs and control information to the IRD  132  at the receiver station  130  via downlink  118 . The IRD  132  receives this information using the subscriber antenna  112 , to which it is communicatively coupled. 
   The video distribution system  100  can comprise a plurality of satellites  108  in order to provide wider terrestrial coverage, to provide additional channels, or to provide additional bandwidth per channel. In one embodiment of the invention, each satellite comprises 16 transponders to receive and transmit program material and other control data from the uplink center  104  and provide it to the subscribers  110 . However, using data compression and multiplexing techniques the channel capabilities are far greater. For example, two-satellites  108  working together can receive and broadcast over  150  conventional (non-HDTV) audio and video channels via 32 transponders. 
   While the invention disclosed herein will be described with reference to a satellite based video distribution system  100 , the present invention may also be practiced with terrestrial-based transmission of program information, whether by traditional broadcasting means, cable, or other means. Further, the different functions collectively allocated among the control center  102  and the uplink center  104  as described above can be reallocated as desired without departing from the intended scope of the present invention. 
   Although the foregoing has been described with respect to an embodiment in which the program material delivered to the subscriber is video (and audio) program material such as a movie, the foregoing method can be used to deliver program material comprising purely audio information or data as well. 
     FIG. 2  is a block diagram showing a typical uplink configuration for a single satellite  108  transponder, showing how video program material is uplinked to the satellite  108  by the control center  102  and the uplink center  104 .  FIG. 2  shows three video channels (which could be augmented respectively with one or more audio channels for high fidelity music, soundtrack information, or a secondary audio program for transmitting foreign languages), and a data channel from a computer data source  206 . 
   The video channels are provided by a program source of video material  200 A- 200 C (collectively referred to hereinafter as video source(s)  200 ). The data from each video program source  200  is provided to an encoder  202 A- 202 C (collectively referred to hereinafter as encoder(s)  202 ). Each of the encoders accepts a presentation time stamp (PTS) from the controller  216 . The PTS is a wrap-around binary time stamp that is used to assure that the video information is properly synchronized with the audio information after encoding and decoding. A PTS time stamp is sent with each I-frame of the MPEG encoded data. 
   In one embodiment of the present invention, each encoder  202  is a second generation Motion Picture Experts Group (MPEG-2) encoder, but other decoders implementing other coding techniques can be used as well. The data channel can be subjected to a similar compression scheme by an encoder (not shown), but such compression is usually either unnecessary, or performed by computer programs in the computer data source (for example, photographic data is typically compressed into *.TIF files or *.JPG files before transmission). After encoding by the encoders  202 , the signals are converted into data packets by a packetizer  204 A- 204 F (collectively referred to hereinafter as packetizer(s)  204 ) associated with each source  200 ,  206 - 210 . 
   The data packets are assembled using a reference from the system clock  214  (SCR), a control word (CW) generated by the conditional access manager  208 , and a system channel identifier (SCID) generator  210  that associates each of the data packets that are broadcast to the subscriber with a program channel. This information is transmitted to the packetizers  204  for use in generating the data packets. These data packets are then multiplexed into serial data, encoded, modulated, and transmitted. A special packet known as a control word packet (CWP) which comprises control data including the control word (CW) and other control data used in support of providing conditional access to the program material is also encrypted and transmitted. 
     FIG. 3A  is a diagram of a representative data stream. The first packet segment  302  comprises information from video channel  1  (data coming from, for example, the first video program source  200 A). The next packet segment  304  comprises computer data information that was obtained, for example from the computer data source  206 . The next packet segment  306  comprises information from video channel  5  (from one of the video program sources  200 ), and the next packet segment includes information from video channel  1  (again, coming from the first video program source  200 A). The data stream therefore comprises a series of packets from any one of the data sources in an order determined by the controller  216 . The data stream is encrypted by the encryption module  218 , modulated by the modulator  220  (typically using a QPSK modulation scheme), and provided to the transmitter  222 , which broadcasts the modulated data stream on a frequency bandwidth to the satellite via the antenna  106 . 
   Subscribers  110  receive media programs via a subscriber receiver or IRD  132 . Using the SCID, the IRD  132  reassembles the packets to regenerate the program material for each of the channels. As shown in  FIG. 3A , null packets created by the null packet module  212  may be inserted into the data stream as desired. 
     FIG. 3B  is a diagram of a data packet. Each data packet (e.g.  302 - 316 ) is  147  bytes long, and comprises a number of packet segments. The first packet segment  320  comprises two bytes of information containing the SCID and flags. The SCID is a unique 12-bit number that uniquely identifies the data packet&#39;s data channel. The flags include 4 bits that are used to control whether the packet is encrypted, and what key must be used to decrypt the packet. The second packet segment  322  is made up of a 4-bit packet type indicator and a 4-bit continuity counter. The packet type identifies the packet as one of the four data types (video, audio, data, or null). When combined with the SCID, the packet type determines how the data packet will be used. The continuity counter increments once for each packet type and SCID. The next packet segment  324  comprises 127 bytes of payload data, which is a portion of the video program provided by the video program source  200 . The final packet segment  326  is data required to perform forward error correction. 
   Encryption of Media Programs 
   Media programs are encrypted by the encryption module  218  before transmission to assure that they are received and viewed only by authorized subscribers. Each media program is encrypted according to an alphanumeric encryption key referred to hereinafter as a control word (CW). This can be accomplished by a variety of data encryption techniques, including symmetric algorithms such as the data encryption standard (DES) and asymmetric algorithms such as the Rivest-Shamir-Adleman (RSA) algorithm. 
   To decrypt the media programs, the subscriber&#39;s  110  IRD  132  must also have access to the CW. To maintain security, CWs are not transmitted to the IRD  132  plaintext. Instead, CWs are encrypted before transmission to the subscriber&#39;s IRD  132 . The encrypted CW is transmitted to the subscriber&#39;s IRD  132  in a control word (data) packet. 
   In one embodiment, the data in the CWP, including the CW, is encrypted and decrypted via what is referred to hereinafter as an input/output (I/O) indecipherable algorithm. 
   An I/O indecipherable algorithm is an algorithm that is applied to an input data stream to produce an output data stream. Although the input data stream uniquely determines the output data stream, the algorithm selected is such that it&#39;s characteristics cannot be deciphered from a comparison of even a large number of input and output data streams. The security of this algorithm can be further increased by adding additional functional elements which are non-stationary (that is, they change as a function of time). When such an algorithm is provided with identical input streams, the output stream provided at a given point in time may be different than the output stream provided at another time. 
   So long as the encryption module  218  and the IRD  132  share the same I/O indecipherable algorithm, the IRD  132  can decode the information in the CWP to retrieve the CW. Then, using the CW, the IRD  132  can decrypt the media program so that it can be presented to the subscriber  110 . 
   To further discourage piracy, the control data needed to decrypt and assemble data packets into viewable media programs may be time-varying (the validity of the control data in a CWP to decode a particular media program changes with time). This can be implemented in a variety of ways. 
   For example, since each CWP is associated with a SCID for each media program, the SCID related to each CWP could change over time. 
   Another way to implement time-varying control data is to associate time stamps with the received data stream and the CWP control data. In this case, successful decoding of the CWP to produce the CW would require the proper relationship between the time stamps for the data stream and the control data in the CWP. This relationship can be defined, for example, by changing the decryption scheme used to generate the CW from the CWP according to the received time stamp for the data stream. In this case, if the time stamp of the received data stream does not match the expected value, the wrong decryption scheme will be selected and the proper CW (to decrypt the program material) will not be produced. If, however, the time stamp of the received data stream matches the expected value, the proper decryption scheme will be selected, and the CWP decryption scheme will yield the proper CW. 
   Requesting Pay-Per-View Services 
   The data required to receive pay-per-view (PPV) media programs are stored in the CWP and in another data packet known as the purchase information parcel (PIP). Both the CWP and the PIP are broadcast to the subscriber via the video distribution system  100  in real time. As described below, the CWP is used by the IRD  132  to retrieve PPV media programs. 
   Generally, PPV services can include operator-assisted pay-per-view (OPPV) and impulse pay-per-view (IPPV) services. When requesting OPPV services, the subscriber  110  must decide in advance that they desire access to a particular media program. The subscriber  110  then calls an entity such as the control center  102 , and requests access to the media program. When requesting impulse pay-per-view services (IPPV), the subscriber  110 , while viewing the program guide, moves the cursor over the viewer channel associated with the desired media program, and selects “enter.” After the decision and rights to purchase a PPV program are confirmed (for example, by checking channel lockouts, rating limits, and purchase limits), a purchase information parcel (PIP) is received and stored in the subscriber&#39;s conditional access module  406  (which is described in more detail below) for further use. The conditional access module  406  associates the information in the CWP and the PIP, and uses the PIP in conjunction with the CWP to verify that the subscriber  110  should be provided access to the media program and to decrypt the media program. 
   Ordering PPV media programs in advance using the PIP is limited, however, since the PIP is broadcast up to 24 hours before the media program itself is broadcast. Since the PIP is broadcast in real time, the IRD  132  does not acquire the PIP until the subscriber  110  actually requests the PPV media program purchase. 
   Subscriber Reception and Decryption of Media Programs 
     FIG. 4  is a simplified block diagram of an IRD  132 . The IRD  132  receives and decrypts the media programs broadcast by the video distribution system  100 . These media programs are streamed to the IRD  132  in real time, and may include, for example, video, audio, or data services. 
   The IRD  132  is communicatively coupleable to a conditional access module (CAM)  406 . The CAM  406  is typically implemented in a smart card or similar device, which is provided to the subscriber  110  to be inserted into the IRD  132 . The CAM  406  interfaces with a conditional access verifier (CAV)  408  which performs at least some of the functions necessary to verify that the subscriber  110  is entitled to access the media programs. The CAV  408  is communicatively coupled to a metadata analysis module (MAM)  411 . Using the information in metadata table (e.g. Table 1 described below), the MAM  411  acts as a gate-keeper to determine whether stored media programs will be decrypted and presented to the subscriber  110 . This is accomplished by comparing the metadata values with measured or accumulated values. The CAV  408  and the MAM  411  can be implemented as separate modules from the transport/demux/decryptor  412  and the microcontroller and memory  414  as shown, or may be implemented via software instructions stored in the memory and performed by the microcontroller  414 . The functionality of the MAM  411  can also be implemented in the verifier  410  or in software resident elsewhere in the IRD  132 . 
   The IRD  132  comprises a tuner  410 , a transport and demultiplexing module (TDM)  412 , which operates under control of a microcontroller and associated memory  414 , a source decoder  416  and communicatively coupled random access memory (RAM)  418 , and a user I/O device for accepting subscriber  110  commands and for providing output information to the subscriber. 
   The tuner receives the data packets from the video distribution system and provides the packets to the TDM  412 . Using the SCIDs associated with each media program, the TDM  412  reassembles the data packets according to the channel selected by the subscriber  110 , and unencrypts the media programs using the CW key. The TDM  412  can be implemented by a single secure chip, and is communicatively coupled to a microcontroller and memory  414 . 
   Once the media programs are unencrypted, they are provided to the source decoder  416  which decodes the media program data according to MPEG or JPEG standards as appropriate. The decoded media program is then provided to a D/A converter (if necessary) and provided to external interfaces  404  which can include a media program presentation device such as a television, an audio system, or a computer. The source decoder  416  makes use of communicatively coupled RAM  418  to perform these functions. 
   The CW key is obtained from the CWP using the CAV  408  and the CAM  406 . The TDM  412  provides the CWP to the CAM  406  via the CAV  408 . The CAM  406  uses the I/O indecipherable algorithm to generate the CW, which is provided back to the TDM  412 . The TDM  412  uses the CW to decrypt the media programs. In most IRDs  132 , the CAV  408  and the CAM  406  are capable of decrypting one video/audio/data media program at a time. 
   As described above, to discourage potential pirates, the control data in the CWP used to decode a particular media program may change with time so that it only produces the proper CW when applied to a media program having the proper time stamp. In this case, the CAM  406  can select and/or control the decryption scheme (e.g. the I/O indecipherable algorithm) according to the time stamp associated with the data stream carrying the media program. If the media program is sufficiently disassociated in time, the improper decryption scheme will be used, and the proper CW to decode the media program will not be produced. 
   Further details regarding the encryption and decryption of media programs can be found in co-pending and commonly assigned U.S. patent application Ser. No. 09/491,959. 
   Storage and Retrieval of Media Programs in Encrypted Form 
     FIG. 5A  is a diagram presenting exemplary method steps used to practice one embodiment of the present invention. A data stream  501  is provided by the subscriber antenna  112  and received by the tuner  410  and the TDM  412 , as shown in block  502 . The data stream  501  includes a plurality of data packets including data packets with the program material encrypted according to a first encryption key (CW key  546  as seen in FIG.  5 B), and one or more control word packets (CWP)  504 . The control word packets  504  contain access control information and other data which may be processed to produce the CW key  546  necessary to decrypt the program material. 
   The data stream  501  may also include metadata describing information including rights associated with the program material (which may include, for example, replay rights and/or copy rights). These rights include parameters necessary for controlling the replay of program material, including IPPV or pay-per-play services. The metadata can include information as described in Table I below: 
   
     
       
             
             
             
           
         
             
               TABLE I 
             
             
                 
             
             
               Right 
               Value 
               Comment 
             
             
                 
             
           
           
             
               Storage 
               N 0   
               N 0  index indicates whether the program 
             
             
                 
                 
               material is permitted to be stored long-term 
             
             
                 
                 
               on the media storage device 528 (value 1) or 
             
             
                 
                 
               if it was intended for real time viewing only 
             
             
                 
                 
               (value 0). 
             
             
               Lifetime without 
               N 1   
               N 1  index indicates how long an item is 
             
             
               purchase 
                 
               permitted to be stored onto the media storage 
             
             
                 
                 
               device 528 without actually being purchased. 
             
             
                 
                 
               This time period could be days, weeks or 
             
             
                 
                 
               months depending on the business case. 
             
             
                 
                 
               When/if this time limit is reached, the 
             
             
                 
                 
               associated program material is erased from 
             
             
                 
                 
               the media storage device 528. 
             
             
               Lifetime after 
               N 2   
               N 2  index indicates how long program 
             
             
               purchase 
                 
               material is permitted to be stored onto the 
             
             
                 
                 
               hard disk after being purchased. This time 
             
             
                 
                 
               period could be days, weeks or months 
             
             
                 
                 
               depending on the business case. When/if this 
             
             
                 
                 
               time limit is reached, the associated program 
             
             
                 
                 
               is erased from the media storage device 528. 
             
             
               Views per pay 
               N 3   
               N 3  index indicates how many times a 
             
             
                 
                 
               subscriber is permitted to use/view the 
             
             
                 
                 
               program material per times it was paid for. 
             
             
                 
                 
               For example, a value of 0 could indicate 
             
             
                 
                 
               unlimited use, and any non-zero value could 
             
             
                 
                 
               indicate how may uses are allowed per pay. 
             
             
               Repurchase a 
               N 4   
               N 4  indicates the cost associated with 
             
             
               program 
                 
               repurchasing a program after the N 3  value 
             
             
                 
                 
               has been exceeded (assuming N 3  is not 
             
             
                 
                 
               unlimited). Depending on the business case, 
             
             
                 
                 
               N 4  may or may not be higher or lower than 
             
             
                 
                 
               the original purchase offer price. 
             
             
               Views per 
               N 5   
               N 5  would indicate how many times a user 
             
             
               repurchase 
                 
               would be able to use/view the program 
             
             
                 
                 
               material after it had been purchased once. 
             
             
                 
                 
               For example, a value of 0 could indicate 
             
             
                 
                 
               unlimited use, and any non-zero value could 
             
             
                 
                 
               indicate how may uses are allowed per pay. 
             
             
                 
                 
               Depending on the business case, the value 
             
             
                 
                 
               for N 5  may or may not be the same as N 3 . 
             
             
               Reserved 
               N 6  - 
               Reserved values to place additional limits on 
             
             
                 
               N M   
               the usage of downloaded materials. The 
             
             
                 
                 
               value of M could be as large or as small as 
             
             
                 
                 
               needed depending on the complexity of the 
             
             
                 
                 
               desired business case. 
             
             
                 
             
           
        
       
     
   
   If the program material is not to be stored in the media program storage device  528  (as indicated by the switch controlled by N 0 ), the encrypted program material  506  and the CWP  504  are processed normally, as shown in FIG.  5 B. The CWP  504  is presented to the IPPV control module in the CAM  406  which analyzes the access control information in the CWP  504  to determine whether or not the subscriber is entitled to view the program material. If so, the CW extraction module  544  produces the control word from data in the CWP and supplies it to the broadcast decrypt module  510  to decrypt the program material  511  for display. 
   The information describing the subscriber&#39;s rights to view the program material (e.g. Table I) may have been previously received from the service provider or from an IPPV purchase action or a subscriber-initiated action preceding the viewing of the program. The subscriber action commands the IPPV control module  540  in the CAM  406  to store IPPV entitlement information in the purchase history module  542  in the CAM  406  for later reporting to the service provider. 
   In one embodiment, the metadata table is initially provided to the subscriber with defaults for each of the settings, and/or is supplied as a part of the IRD  132  software. When a program is broadcast that is to be stored onto the hard disk for storage and later PPV, the default metadata table is attached (e.g. by the IRD  132  verifier  408 ). For the majority of the broadcasted events and programs, the default settings are sufficient, and no further changes are required. 
   If a need arises to change one of the settings for a particular program, the change to the specific parameter, and not the entire metadata table, is broadcast to the subscriber. The IRD  132  then recognizes the parameter change, and modifies the metadata table according to the specific parameter change. This way, the broadcaster is required only to broadcast the non-default values, and not the same table for each program. This saves valuable broadcast bandwidth and IRD  132  operations required to build and store multiple metadata tables. 
   The metadata could also be used to pre-cache content onto a subscriber&#39;s  110  storage device  528 . The content would be “hidden” from the subscriber  110  until a specified time and/or date, or another condition (which can be described in the metadata table) takes place. For example, the program title would not initially be presented in the available cache or other areas of the user interface. After the appropriate condition is satisfied (e.g. at the appropriate time), the content would then be presented to the subscriber  110  as an available program. This would allow the video broadcast system to send content at opportune times for broadcast, such as during the night when bandwidth demands are low. This can happen either the day of an event or even weeks ahead of time. These pre-cached events could be triggered to present content that relates to either special events or during times and dates specified by the content providers. 
   The metadata can also be provided as a part of the data stream  501  from a different satellite  108  transponder than the program material, from a different satellite  108 , or from a land link such as the PSTN link  120 . 
   After suitable processing (i.e. MPEG and or JPEG decoding, decompression, conversion to an analog signal, etc.), the program material  511  is provided to an external interface  404  device, which may include a presentation device such as a display  548 . 
   If the program material is to be stored in the media program device  528 , the encrypted program material  506  (denoted Encrypted V/A/D in  FIGS. 5A-5C  to indicate that the program material can include video, audio, or other data) is provided to a storage encryption module  512 . The storage encryption module  512  further encrypts the encrypted program material  506  and the CWP  504  according to a CP encryption key  516 . Further, a key encryption module  522  encrypts the CP key  516  with a box key  520  to produce an encrypted CP key  524 . The resulting further encrypted program material  514 , the encrypted CWP  518 , and the encrypted CP key  524  are stored in the media storage device  528 , as shown in block  526 . When replay of the stored program material is desired, the further encrypted program material  514 , the encrypted CWP  518  and the encrypted CP key  524  are retrieved from the media storage device  528  as depicted in block  530 . Using the box key  520 , the encrypted CP key  524  is decrypted by the key decryption module  532  to produce the CP key  516 . The CP key  516 , the further encrypted program material  514  and the encrypted CWP  518  is provided to the storage decrypt module  534 . Using the CP key  516 , the CP decrypt module  534  produces the encrypted program material  506  (still encrypted with the CW key as it was when it was received by the tuner  410 ) and the CWP  504  (which is again in the same form as it was when it was received by the tuner  410 ). 
   Should the storage device  528  fail, the data stored therein may still be recovered. Unlike prior art video storage devices, which prevent copying of the data from the storage media via a controller that writes data to the storage media, the present invention stores the data in encrypted form as well as at least part of the information required 
   Since the present invention stores data in encrypted form as well as a key required to decrypt the data (using other keys in the IRD  132 ), the present invention allows the user to back up data stored in the media storage device  528  on another data storage device such as a zip drive or a writable CD ROM. Further, the such backup data is encrypted, and not exposed to copying. 
     FIG. 5B  is a diagram showing additional operations performed when the subscriber  110  elects to view program material stored on the media storage device  528 . 
   When the subscriber  110  elects to view recorded program material, the MAM  411  compares the metadata associated with the program material (which may include data regarding the rights shown in Table I above) with other stored information to determine whether the recorded program material should be decrypted and presented. If the comparisons performed by the MAM  411  indicate that the stored program material should be decrypted and presented to the subscriber  110 , the CWP  504  is provided to the CAM  406 . The CAM  406  includes an IPPV (impulse pay-per-view) control module  540  which commands CW extraction module  544  to decrypt the CWP  504  to produce the CW  546 , and provides information regarding the subscriber&#39;s  110  decision to purchase the right to view the program material to a purchase history module  542 . The purchase history module  542  records information regarding the subscriber&#39;s  110  purchase, and provides the information to the entity that provided the program material to the subscriber for billing purposes. The IPPV control module  540  essentially performs the same functions as that which would be required for non-storage compatible operations. Hence, the foregoing functionality is accomplished without resort to changes in CAM  406  functionality. 
   Importantly, the embodiment described above does not require changes to the CAM  406 , since the operations described in  FIG. 5B  are exactly the same as normal operation when the program material is not stored on the media storage device. Further, this embodiment does not require alteration of the CWP  504  to account for any temporally varying relationship between the information in the CWP  504  and the program material. That is because any time-dependent relationship between the SCIDs of the program material and the CWP are preserved when they are encrypted and stored on the media storage device. 
     FIG. 5C  is a diagram showing an embodiment of the present invention in which the unencrypted program material is re-encrypted and stored on the data storage device  528  (or a second data storage device separate from the data storage device  528 ) and retrieved for presentation to the subscriber  110 . This embodiment is useful, for example, to support the enforcement of the replay and copy protection rights described in Table I. This embodiment is also useful when the subscriber  110  requests trick play operations in viewing program material stored on the media storage device  528 . These trick play operations include, for example, a play command; a rewind command; a fast forward command; a fast reverse play command; a fast forward play command; a pause command; a frame step command; and a stop command. 
   In this embodiment, the unencrypted program material  511  is not provided directly for display, but rather copy protection encrypted, stored in the data storage device  528  (or a second data storage device), and retrieved and decrypted before providing the program material for display. In particular, the unencrypted program material  511  is provided to a second Storage Encrypt Module  550 . The second Storage Encrypt Module  550  encrypts the unencrypted program material  511  using the CP encryption key  516  to produce re-encrypted program material  552 . The CP encryption key  516  is also encrypted by the key encrypt module  522  to produce the encrypted CP key  524 . Both the re-encrypted program material  552  and the encrypted CP key  524  are stored in the media storage device  528 . 
   When a user command is provided to the user I/O  420  that requires playback of the program material, the re-encrypted program material  552  and encrypted CP key  524  are retrieved from the media storage device  528 . The encrypted CP key is decrypted by the key decrypt module  532  to produce the CP encryption key  516 . The re-encrypted program material  552  and the CP encryption key  516  is provided to a storage decrypt module  554 . The storage decrypt module  554  decrypts the re-encrypted program material  552  to produce a clear version of the program material  511 . The program material  511  is provided to an external interface  404  such as the display  548  for presentation to the user. 
   In the preferred embodiment, the storage encrypt module  550  and decrypt modules  554  described above with respect to  FIG. 5C  are different modules than that which are described and illustrated in FIG.  5 A. This allows parallel encryption operations to be performed, thus speeding up the process, and allowing for the application of different CP encryption keys. However, the present invention may also be implemented such that the same CP encrypt and decrypt modules are used for both operations. This includes an implementation where different CP keys are used, and switched into the modules as required. 
   Similarly, it should be noted that  FIGS. 5A and 5C  illustrate an embodiment wherein the storage encrypt and storage decrypt modules  550 ,  554  are separate modules. However, the present invention may also be implemented with a single Storage Encryption and Decryption module, which may be switched between encrypt and decrypt functionality. 
   Similarly, the key encrypt and decrypt functionality described in  FIGS. 5A and 5C  are illustrated as separate modules, whereas the same optional usage of one or more modules may be utilized to perform the functionality. 
   The present invention also envisions the use of the same or similar encryption mechanisms are used for the broadcast decryption, storage encryption and decryption, and key encryption and decryption to allow one or more such modules to perform any of the encrypt or decrypt functions described in  FIGS. 5A and 5C . 
   Generally, the box key  520  is unique to the IRD  132  and the CP key is unique to the media program, but this need not be the case. Further, different techniques and mechanisms can be used to generate and install the IRD-unique box key  520  and the media program unique CP key. In a preferred embodiment, the box key  520  is factory configured, and the CP key is generated randomly by the IRD  132 , and is unique for each stored media program. 
   Finally, it is noted that in the embodiment described above, the media storage device  528  depicted in  FIG. 5C  is the same media storage device  528  depicted in FIG.  5 A. If desired, however, the re-encrypted program material  552  can be stored in a second (and separate) media storage device. For that matter, any of data described in the foregoing can be stored in a plurality of media storage devices to increase throughput or facilitate additional security measures. This embodiment would permit faster storage and retrieval of information from the disk(s). 
   In the foregoing embodiment of the present invention, the data stream received in IRD  132  further includes metadata including data to control replay rights and copy protection. This metadata is stored in the media storage device  528  for later use when a request to view the media program is received. The stored metadata may or may not be encrypted and/or signed. 
   Conclusion 
   The present invention describes a system and method for recording program related material that has not yet been purchased, and allow IPPV purchase at the time of replay and viewing. Billing will only be applied if the purchase is made. The data stream  501  having the program material is subject to different limitations on such storage and replay depending on the associated metadata for each program. The program material can be presented to the subscriber  110  in real time, or can be further encrypted prior to storage for later-playback. In either case, program material is not stored plaintext. Caching techniques can be used to allow the user to delay or shift a program, or to support trick play functions. 
   When the program material and associated data is not intended to be stored on the hard disk for later playback, the IRD  132  sends the encrypted program material  506  and associated CWP  504  to the CAM  406 . The CAM  406  decrypts the CWP  504  to obtain the CW key  546 , and the CW key  546  is used to decrypt the program material so that it can be presented to the subscriber  110 . 
   If a media storage device  528  is available to the IRD  132 , the media program can be decrypted, re-encrypted, and stored in the media storage device as a cache to allow the user to pause, rewind, fast forward or any other functions that might be incorporated as part of trick play functions. 
   If a media storage device  528  is available to the IRD  132  and the data is to be stored on the hard disk prior to purchase for later purchase and playback, the IRD  132  bypasses CAM  406  processing and sends the encrypted program material  506  and associated CWP  504  directly to an encryptor engine  512  (typically included within the transport chip) and bypass being processed by the CAM. Once the data is further encrypted, the information is stored. 
   The present invention uses metadata associated with each media program that is included in the broadcast data stream. The metadata includes information describing the rights available to the subscriber  110  in terms of viewing and/or copying the program material. The “rights” associated with the program material could be presented to the subscriber  110  in a user-friendly manner. 
   The “rights” described in the metadata may allow the subscriber to view a media program an unlimited number of times within a time period (video store model); a set number of times within a time period (modified video store model); allow the user only one play within a set time period (movie theater model); and allow different pricing models for the different views (i.e. pay 1× for the first usage, ½× for second viewing, etc.). Other models would allow storage of media programs for set availability windows and then automatically delete the programs after the availability window is closed. Because the access control information as well as the associated program material, the present invention can be effectively utilized in systems in which the access control information is time-varying. 
   Typically, the IRD  132  handles the generation, encryption, and decryption of the encryption keys. The IRD  132  also includes the necessary hardware and software to install and restore keys for copy protected service. 
   While the foregoing description has focused primarily on the storage and retrieval of video programs, the present invention is not limited to these media types. As such, the terms “media program” or “program material” describe a video data stream, and/or an audio data stream, and/or any other broadcast data stream, regardless of the data type. 
   The foregoing description of the preferred embodiment of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto. The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.