Abstract:
A method and apparatus for storing and retrieving program material for subsequent replay is disclosed. The method comprises the steps of receiving a data stream comprising the program material encrypted according to a first encryption key, decrypting the program material; re-encrypting the program material according to a second encryption key; and storing the re-encrypted material in a media storage device. The program material is played back by retrieving the re-encrypted material from the media storage device and decrypting the re-encrypted program material. In one embodiment, the second encryption key is derived from metadata describing replay rights. In a further embodiment, the media storage device also stores the second encryption key which has been further encrypted by a key that is unique to the device used to receive the program material.

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. 09/621,476, 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. James, filed on Jul. 21, 2000, now issued as U.S. Pat. No. 7,203,311; 
     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). Gagnon, David D. Ha, Peter M. Klauss, Christopher P. Curren, and Thomas H. James, filed on Jul. 21, 2000; 
     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 Jul. 21, 2000, now issued as U.S. Pat. No. 7,203,314; 
     U.S. patent application Ser. No. 09/620,832, entitled “VIDEO ON DEMAND PAY PER VIEW SERVICES WITH UNMODIFIED 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 Jul. 21, 2000, now issued as U.S. Pat. No. 6,853,728; 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, now issued as U.S. Pat. No. 6,701,528. 
     This application is also related to the following applications: 
     application Ser. No. 09/590,417, entitled “METHOD AND APPARATUS FOR TRANSMITTING, RECEIVING, AND UTILIZING AUDIO/VISUAL SIGNALS AND OTHER INFORMATION”, filed Jun. 8, 2000, by Arthur Tilford; 
     application Ser. No. 09/960,824 entitled “METHOD AND APPARATUS FOR ENCRYPTING MEDIA PROGRAMS FOR LATER PURCHASE AND VIEWING”, filed Sep. 21, 2001, by Raynold M. Kahn et al.; 
     application Ser. No. 10/490,261 entitled “METHOD AND APPARATUS FOR CONTROLLING PAIRED OPERATION OF A CONDITIONAL ACCESS MODULE AND AN INTEGRATED RECEIVER AND DECODER”, filed Aug. 5, 2004, by Raynold M. Kahn et al., which is a national stage entry of PCT/US02/29881 filed Sep. 20, 2002; 
     application Ser. No. 10/758,811 entitled “DISTRIBUTION OF VIDEO CONTENT USING A TRUSTED NETWORK KEY FOR SHARING CONTENT”, filed Jan. 16, 2004, by Raynold M. Kahn et al; 
     application Ser. No. 10/758,818 entitled “DISTRIBUTION OF BROADCAST CONTENT FOR REMOTE DECRYPTION AND VIEWING”, filed Jan. 16, 2004, by Raynold M. Kahn et al; 
     application Ser. No. 10/758,865 entitled “DISTRIBUTION OF VIDEO CONTENT USING CLIENT TO HOST PAIRING OF INTEGRATED RECEIVERS/DECODERS”, filed Jan. 16, 2004, by Raynold M. Kahn et al; 
     application Ser. No. 10/790,466 entitled “VIDEO ON DEMAND IN A BROADCAST NETWORK”, filed Mar. 1, 2004, by Stephen P. Dulac; 
     application Ser. No. 11/433,926 entitled “METHODS AND APPARATUS TO PROTECT CONTENT IN HOME NETWORKS”, filed May 15, 2006, by Raynold M. Kahn; 
     application Ser. No. 11/433,969 entitled “METHODS AND APPARATUS TO PROVIDE CONTENT ON DEMAND IN CONTENT BROADCAST SYSTEMS”, filed May 15, 2006, by Peter M. Klauss et al.; 
     application Ser. No. 11/434,082 entitled “CONTENT DELIVERY SYSTEMS AND METHODS TO OPERATE THE SAME”, filed May 15, 2006, by Raynold M. Kahn et al.; 
     application Ser. No. 11/434,404 entitled “SECURE CONTENT TRANSFER SYSTEMS AND METHODS TO OPERATE THE SAME”, filed May 15, 2006, by Raynold M. Kahn et al; 
     application Ser. No. 11/434,437 entitled “METHODS AND APPARATUS TO CONDITIONALLY AUTHORIZE CONTENT DELIVERY AT RECEIVERS IN PAY DELIVERY SYSTEMS”, filed May 15, 2006, by Raynold M. Kahn et al.; 
     application Ser. No. 11/434,528 entitled “METHODS AND APPARATUS TO CONDITIONALLY AUTHORIZE CONTENT DELIVERY AT BROADCAST HEADENDS IN PAY DELIVERY SYSTEMS”, filed May 15, 2006, by Raynold M. Kahn et al.; 
     application Ser. No. 11/434,538 entitled “METHODS AND APPARATUS TO CONDITIONALLY AUTHORIZE CONTENT DELIVERY AT CONTENT SERVERS IN PAY DELIVERY SYSTEMS”, filed May 15, 2006, by Raynold M. Kahn et al.; 
     application Ser. No. 11/499,635 entitled “DISTRIBUTED MEDIA-PROTECTION SYSTEMS AND METHODS TO OPERATE THE SAME”, filed Aug. 4, 2006, by Michael Ficco; 
     application Ser. No. 11/499,636 entitled “DISTRIBUTED MEDIA-AGGREGATION SYSTEMS AND METHODS TO OPERATE THE SAME”, filed Aug. 4, 2006, by Michael Ficco; 
     application Ser. No. 11/501,985 entitled “SECURE DELIVERY OF PROGRAM CONTENT VIA A REMOVAL STORAGE MEDIUM”, filed Aug. 10, 2006, by Raynold M. Kahn et al.; and 
     application Ser. No. 11/654,752 entitled “SECURE STORAGE AND REPLAY OF MEDIA PROGRAMS USING A HARD-PAIRED RECEIVER AND STORAGE DEVICE”, filed Jan. 18, 2007, by Raynold M. Kahn et al., which is a continuation of application Ser. No. 09/620,833, entitled “SECURE STORAGE AND REPLAY OF MEDIA PROGRAMS USING A HARD-PAIRED RECEIVER AND STORAGE DEVICE”, filed Jul. 21, 2000, by Raynold M. Kahn et al., which application is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to systems and niethods 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 digital 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 integrated receiver/decoder (IRD), or the conditional access module (CAM) that is used to provide a 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 a data stream comprising the program material encrypted according to a first encryption key, decrypting the program material; re-encrypting the program material according to a second encryption key; and storing the re-encrypted material in a media storage device. The program material is played back by retrieving the re-encrypted material from the media storage device and decrypting the re-encrypted program material. In one embodiment, the second encryption key is derived from metadata describing replay rights. In a further embodiment, the media storage device also stores the second encryption key which has been further encrypted by a key that is unique to the device used to receive the program material. 
     The apparatus comprises a tuner, for receiving a data stream comprising encrypted access control information and the program material encrypted according to a first encryption key, the access control information including a first encryption key; a conditional access module, for decrypting the encrypted access control information to produce a first encryption key; a first decryption module, for decrypting the program material using the first encryption key; an encryption module, for re-encrypting the decrypted program material according to a second encryption key and for encrypting the second encryption key according to a third encryption key to produce a fourth encryption key; and a second decryption module, for decrypting the fourth encryption key to produce the second encryption key using the third encryption key and for decrypting the re-encrypted program material using the second encryption key. 
     One object of the present invention is to provide a system allowing for growth to pay-per-play or true video-on-demand (VOD) services from media programs stored on a hard disk. The pay-per-play service allows the subscriber to select media programs or games from the real time broadcast data or from the media programs stored on the disk. VOD service permits the subscriber to purchase provided media programs and games from the subscriber&#39;s receiver instantly, without regard to the start time of the program. 
     Another 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 viewed 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. 
     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. At the same time, the present invention can be implemented with minimal changes to the IRD, and no changes to the CAM interface. The present invention also provides a basis for a growth path to more advanced encryption/decryption techniques. 
    
    
     
       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 
         FIG. 5  is a diagram 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 . 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 a communicatively coupled subscriber antenna  112 . 
     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  312  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 the 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 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  410  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. 5  is a diagram presenting exemplary method steps used to practice one embodiment of the present invention. A data stream is provided by subscriber antenna  112  and received by the tuner  410  and the TDM  412 , as shown in block  502 . The data stream includes a plurality of data packets which include the CWP, and program material that is encrypted according to a first (CW) encryption key. The data stream may also include metadata having replay rights. The replay rights are parameters necessary for controlling the replay of IPPV or pay-per-play services. 
     When the subscriber elects to purchase the media program, a viewing request is provided, and an IPPV control module  504  CAM  406  controls whether access to the requested media program will be provided. If so, the purchase history module  506  collects information required to send a bill for the media program to the subscriber  110 . After the purchase history module  506  has acquired and recorded the required information, the IPPV control module  504  commands the CW extraction module  508  to decrypt the CWP to obtain the first (CW) encryption key. In one embodiment, this is performed using a complementary form of the I/O indecipherable algorithm that was used to encrypt the CW and other information to form the CWP. The resulting CW encryption key is provided to a broadcast decrypt module  510 . The broadcast decrypt module  510  uses the CW key to decrypt the media program (hereinafter alternatively referred to as program material) to produce a clear (non-encrypted) version of the media program  512 . The resulting clear media program  512  is applied to a storage encryption module  514 , where the media program is re-encrypted according to a second copy protection (CP) encryption key  516 . This is illustrated in box  514 . In one embodiment, the CP key  516  is used to encrypt and decrypt the media program via an encryption technique such as RSA, or preferably, triple 56-bit DES, DES-X cipher block chaining (CBC). DES is preferred because it is computationally more efficient than RSA in performing time-related computations. In one embodiment, the CP key  516  is a key that is unique to each IRD  132  and is stored therein. 
     The CP key  516  itself is then provided to a key encryption module  522 , where it is encrypted with a third (box) encryption key  520  to produce a fourth encryption key (illustrated in  FIG. 5  as Encrypted CP key  524 ). The box encryption key  520  is unique to each IRD  132 , and is typically hardcoded in the IRD  132 . 
     The re-encrypted program material  518  and the Encrypted CP key  524  is then stored in the media storage device  528  as shown in block  526 . The media storage device  528  could include a hard disk drive, similar to that which is employed in personal computers, a optical-magnetic hard disk drive, an optical disk drive, or any other medium by which data may be recorded for subsequent playback. 
     When the subscriber  110  decides to view the recorded program material, a command is provided to the IRD  132  via the user I/O interface  420 . The re-encrypted program material and the encrypted CP key  524  stored in the media storage device  528  are then retrieved, as shown in block  530 . The encrypted CP key  524  is then provided to decryption module  532 , where it is decrypted with the box key  520  to produce the CP key  516 . 
     The CP encryption key  516  is then provided to the storage decryption module  534 , where the program material is decrypted according to the CP key  516 . The decrypted (and now clear) program material is now provided to a display  536  or other presentation device. 
     In one embodiment, the CP key  516  is modified with (e.g. by appending or adding) some or all of the metadata received in the broadcast data stream before being encrypted according to the box key  520 . In this case, the encrypted CP key  524  not only includes the value of the CP key  516 , but also, the metadata as well. When the encrypted CP key  524  is thereafter retrieved from the storage media  528  and de-encrypted with the box key  520 , the CP key  516  and the metadata is recovered as well. This metadata can be compared to other data (e.g. the data and the time of day) to enforce the replay rights as required. 
     The CP key  516  can be stored in a transport chip within the TDM  412 . This allows the present invention to be used with an unmodified CAM  406 . This also permits rapid encryption and decryption of information stored in the media storage device  528 , which is particularly advantageous where trick play functions are desired. 
     CONCLUSION 
     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. For example, the encryption functions described herein could be performed by separate encryption/decryption modules, or a single multi-purpose encryption/decryption module can be utilized to perform the encryption/decryption functions of many separate modules. 
     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.