Abstract:
A content distribution system and method which prevents unauthorized access to secured content such as movies and music. The system includes a source, a receiver, an authorized security device such as a conditional access module (CAM) for decrypting authorized content and an output device for outputting content. The system can also include a backend for managing accounts and system operations. One aspect of this invention is that the content data is derived from the Internet. The system allows for the verification of authorization to play secured content, the addition of watermarks to the secured content, the conversion of the secured content to a displayable form and the means for preventing output of the secured content.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 09/880,856 to Schumann et al., filed on Jun. 15, 2001, entitled “Digital Content Distribution System and Method,” which claims the benefit of Provisional Application Ser. No. 60/144,833 to Schumann et al., filed on Jan. 9, 1999, entitled “Digital Content Distribution System and Method,” and the benefit of PCT Application Serial No. PCT/US00/00077 to Schumann et al., filed on Jan. 5, 2000, also entitled “Digital Content Distribution System and Method,” the contents of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a secure content distribution system and method. More particularly, the present invention relates to a secure digital content distribution system and method for preventing unauthorized access to said content. More particularly still, the present invention relates to a content protection architecture that may be used to provide for conditional access of data and entertainment products such as movies and music. 
     BACKGROUND OF THE INVENTION 
     Preventing unauthorized access to digital content is an important problem in numerous applications. The present invention broadly relates to and provides a solution to this problem. In some commercial applications, where the content includes, for example, valuable audio or video content, unauthorized access by those who obtain the content may tend to reduce the profit margin of the content provider(s), who typically provide the content, e.g. to various listener and/or viewers, for a fee. In particular, with the advent of high definition video, this problem is even more serious because the digital data is of sufficient resolution to be shown on a full size theater screen. This opens up a whole new area for content pirates to market their stolen property. While the description which follows may sometimes be described in the context of audio/video/data as an example of content to be provided, the invention is not so limited and may equally to any type of information or content data from any source, including without limitation audio and/or video data or other type of data or executables. If the unauthorized accesser is a content pirate, he or she may pose a serious threat to a content provider by inducing others to pirate the content as well. More particularly, the pirate may generally sell pirated access to the content at a lower cost than the legitimate content provider because the pirate obtains access to the content by using the legitimate provider&#39;s infrastructure and therefore does not have to invest resources to produce and disseminate the content. This becomes even a greater concern where the pirate may copy and mass produce a relatively inexpensive component which allows a large number of users to obtain access to the content without authorization by the legitimate content provider. As a result, content providers have resorted to increasingly expensive and complex schemes to prevent unauthorized access to their information and content, i.e. to prevent pirating. 
     The present application is directed to the same general technology as co-pending commonly assigned patent application Ser. No. 09/253,013, entitled “Information Access Control System and Method” naming Goldshlag et al. as inventors (the contents of which are incorporated by reference herein). The present application presents a more complete architecture and method for content distribution. The present invention, while employing many common encryption/decryption techniques with Ser. No. 09/252,013, provides a more comprehensive overall architecture and methodology for securely managing content from content authoring to ultimate display. 
     One plan for controlling access to content involves the use of an IRD (integrated receiver device) with smart cards as a security module. This plan was proposed by Fiat and Schamir in a paper titled “How To Prove Yourself: Practical Solutions To Identification And Signature Problems” The Weizmann Institute of Science, Rehovot Israel (1986), and involves the use a trusted center to encode a smart card with personal information and secret values relating to the access. The smart card proves its identify to a verifier (IRD) which in turn must have knowledge of the secret values used to place the information onto the smart card. While the Fiat-Schamir plan is designed to make it difficult to forge personal information of one card, it does not prevent mass distribution of the forged card when and if the pirate has broken the smart card secrets used to prove identity. Also see, U.S. Pat. No. 4,748,688 to Schamir. 
     Another approach is described in U.S. Pat. No. 5,481,609 to Cohen et al., which uses a smart card in a system for controlling access to broadcast transmissions. Cohen uses a verifier function in an IRD to authenticate the authenticity of a smart card, a secret-learning operation, and a blacklisting operation that prevents previously detected illegal cards from gaining access. However, as indicated by the presence of the blacklisting operation, the system proposed in Cohen et al. can talk to any smart card that is not on the blacklist, and is thus susceptible to a pirated card (or a plurality of pirated cards) that has not yet been blacklisted. Furthermore, the verification process proposed by Cohen et al. is triggered by the broadcast source. Thus, a pirate could simply remove the verification commands from the broadcast stream thereby circumventing the verification process altogether. Another practical problem resulting from use of the broadcast source to trigger the verification process is an architectural one whereby what should be a local level decision (when and whether to challenge a smart card) is turned into a system level decision. Finally, the verification process in Cohen et al. is not tied to the transaction between the smart card and the verifier. Thus, a pirate could use a legitimate card for access authentication, i.e., to authenticate its right to access the content of the broadcast, and then use a pirated card to avoid being billed for the access, i.e. to avoid recording that the access was actually made by the legitimate card holder. This type of pirating is referred to herein as an example of a type of attack known as a conduit attack. 
     Another security approach is described in U.S. Pat. No. 5,461,675 to Diehl et al., which proposes to relate data between successive data packets, thus detecting when a packet has been removed. Particularly, Diehl et al. propose to inform a legitimate smart card when it is being avoided. However, a pirated card could simply ignore such information and provide pirated access to the content. 
     In yet another approach, proposed in U.S. Pat. No. 5,778,068 to Johnson et al., a determination is made whether a processing device and a user device, which contains a storage device, are authorized to operate with each other. The Johnson et al. approach determines whether a user device, in this case, a device which generally corresponds to a set top box, is valid by authenticating the user device to a provider device, in this case, a device which generally corresponds to a backend module. However, this approach does not determine if the provider device is valid, i.e. if the provider device is authorized to operate with the user device or with a provider device. Accordingly, a pirate who successfully reverse engineers and modifies the provider device could overcome the security protocols in Johnson et al., and more importantly, could mass-produce the pirated provider device for distribution to and by users. 
     Another approach is proposed in U.S. Pat. No. 5,825,876 to Peterson, Jr.. Peterson authorizes access through a smart card that delivers key content to a processor that allows a playback device to reproduce content from a recording medium. The system proposed by Peterson uses a public key held at an authorization center and a private key held by the card. However, there is no pairing operation between the card and the processor, and there is no shared secret key between the card and the processor. Therefore, if a pirate successfully broke the encryption mechanism he/she could mass-produce and widely distribute pirated cards, causing harm to the content provider. 
     Another approach is proposed in U.S. Pat. No. 5,448,045 to Clark, which uses a smart card to create a secure boot application on a computer by using the smart card to verify the executable files that the computer will run. The smart card and the computer share a secret that is installed by an administrator and the smart card and the computer executes an authentication operation. However, once an attacker figures out the code, the pirated smart card would be able to authenticate itself. Furthermore, since there is no notion of challenge to the card by the computer, the authentication is replayable. Therefore, a card that is no longer valid may continue to be used. 
     Finally, another approach proposed in U.S. Pat. No. 5,802,176 to Audebert, controls access to a particular function on a computer by using a renewable card. This is a transaction based system in which the card and the computer negotiate access and a key changes each time access occurs. However, this approach is limited to the particular function which is to be accessed on the computer, and is not useful for a system which deals with many different unpredictable functions/programs such in an information dissemination system, i.e. a system in which each different program (movie, song, article, executable, etc.) would be a different function. 
     What is needed is a system and method for protecting valuable content; a method and system which is robust, which may be tailored to the needs of a particular content provider, and which overcomes the above noted deficiencies. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     It is an object of the invention to prevent unauthorized access to content disseminated by a content provider. 
     It is a further object of the invention to prevent a pirate from enabling a large number of persons to obtain unauthorized access to content from a content provider. 
     It is yet another object of the invention to provide a digital content protection architecture that may be used to provide conditional access to data, such as may be found in entertainment products and executables. 
     It is another object of the invention to provide high definition multimedia content on various media including, a DVD optical disc. 
     It is yet a further object of the invention to provide a protocol for packing content data into data packets for compression and transport. 
     To achieve the foregoing and other objects and in accordance with the purpose of the present invention as embodied and broadly described herein, the apparatus of the invention for secure distribution of content may comprise a source for accessing content data; a conditional access module for receiving the content data from the source and selectively processing the content data and selectively authorizing access to decoded processed content data; a receiver for receiving the processed content data from the conditional access module and decoding the processed content data into the decoded processed content data; and an output device for receiving the decoded processed content data from the receiver and outputting the decoded processed content data when authorized by the conditional access module. 
     Further, an apparatus according to the present invention for secure distribution of digital content may comprise a source for accessing content data, the source including a transport packet generation device for transforming the content data into content data packets; a conditional access module for receiving the content data packets from the source and selectively processing the content data packets; a receiver for receiving the processed content data packets from the conditional access module and decoding the processed content data packets; and an output device for outputting the decoded content data, wherein communications between the source, the receiver and the conditional access module utilize at least one packet data protocol. 
     Further, a method according to the present invention for preventing unauthorized access to content data in a system comprising a source, a conditional access module, a receiver and an output device, the method comprising: acquiring content data at the source; transporting the content data to the conditional access module; determining whether access to the content data is authorized; selectively processing the content data; transporting processed content data from the conditional access module to the receiver; decoding the processed content data; selectively providing the decoded processed content data to the output device; and outputting the decoded processed content data when authorized by the conditional access module. 
     Further, a method according to the present invention for preventing unauthorized access to digital content in a system comprising a source, a conditional access module, a receiver and an output device, the method comprising: acquiring content data at the source; transforming the content data into packet data; transporting the packet data from the source to the conditional access module; determining whether access to the packet data is authorized; selectively process the packet data; transporting the processed packet data to the receiver; decoding the processed packet data; and outputting the decoded content. wherein communications between the source, the receiver and the conditional access module utilize at least one packet data protocol. 
     In a further aspect of the invention, the conditional access module may further include a CAM fingerprint logic device for adding a CAM watermark to the content wherein the CAM watermark includes at least one of the following: a time of access of the content data, a serial number of the content data, a source identification value, a receiver identification value, and a conditional access module identification value. 
     In yet a further aspect of the invention, the output device may further include a display device and a watermark logic device, wherein the watermark logic device is operable to extract a watermark from the decoded processed content data; create an extracted watermark data packet from the watermark; output the extracted watermark data packet to the conditional access module; input an authorization from the conditional access module; and output an enable signal to the display device. 
     Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawing, which are incorporated in and form a part of the specification, illustrate an embodiment of the present invention and, together with the description, serves to explain the principles of the invention. 
         FIG. 1  is a block diagram of an embodiment of the present invention. 
         FIG. 2  is a flow diagram depicting an embodiment of the Watermark Logic ( 164 ) of  FIG. 1 . 
         FIG. 3  is a block diagram of an embodiment of an aspect of the present invention wherein a single ATSC transport packet stream may be created which combines several different display streams. 
         FIG. 4  is a diagram depicting an exemplary embodiment of the present invention wherein an ATSC transport packet stream is grouped and packed into DVD sectors. 
         FIG. 5  is a block diagram of an exemplary aspect of the present invention depicting exemplary audio and video streams laid out on an optical disc. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
       FIG. 1  is a simplified block diagram of an embodiment depicting an exemplary digital content distribution system according to the present invention. As shown in  FIG. 1 , a source  100  provides digital content to be displayed. This digital content may be derived from any number of potential signal sources including but not limited to an HD-DVD (High Definition Digital Versatile Disc), a terrestrial or satellite broadcast, a cable broadcast, a digital VCR, a computer, a set-top box, or the internet. 
     The source  100 , acquires pre-authored content  103  from a content source, formats it and encrypts it so that it may be sent to a receiver  120  over an exposed interface  110 . 
     Content  103  is typically authored movies and other multimedia data and applications and may be encrypted by any known encryption algorithm including but not limited to: TripleDES, DES, IDEA, or SKIPJACK. In the illustrated embodiment, the optical disc  102  comprises a DVD with a modified logical structure. One skilled in the art will appreciate that any type of media or disc capable of storing digital data may be used. The process of formatting and preparing content for recording on an optical disc  102  (also known as authoring) will be described below. 
     A media drive  107 , is preferably a DVD disk drive capable of reading digital content  103  from the optical disc  102 . This drive may include specialized hardware for reading any specially recorded optical disc  102 . For standard optical discs, the structure of the media drive  107  is well known. The media drive  107  is controlled by a source control logic  109 . 
     The digital content  103  read from the optical disc is input to a transport packet generation device  104 , where DVD sectors  450  are processed to reclaim modified Advanced Television Systems Committee (“ATSC”) transport packets which are then inserted into the content data stream as transport packets. The transport packet generation device  104  may also insert commands for a receiver  120  and a conditional access module  140  (“CAM”) into the content data stream. The transport packet generation device  104  is controlled by the source control logic  109 . The digital content  103 , in the form of DVD sectors  450  ( FIG. 4 ) are processed sequentially. First, each DVD Sector Header  410  ( FIG. 4 ) is analyzed to determine how to reconstruct the modified ATSC transport packets packed in sector  410  ( FIG. 4 ). First, a determination is made as to the type of each packet by analyzing the packet type. Then using unique information in the header, ATSC packet header data is retrieved from the DVD sector. This retrieved packet header data is passed to the source control logic  109  which may include pointers which point to the beginning of frames, information that may be used to implement ‘trick’ modes, data that defines and assists in operating the source device, special device applications, special content applications, or the like. 
     Next, the individual ATSC transport packets are degrouped from the DVD sectors. A series of packing packets  401 ,  402 ,  403 ,  404 ,  405  and  406  ( FIG. 4 ) for each type of packet is created. In the case of multiple packets of the same type, for example audio or video packets, a determination is made as to the size of the largest individual packet, and all of the packing packets for that type are then conformed to that size. 
     Each packet so formed is then retrieved from the transport packet generator  104 . If a packet is fractional, it is saved for use when degrouping the next sector. In the illustrated embodiment, a 4-byte header is added back to the packet. It should be understood that the invention not so limited in terms of packet size. Then, consistent with the illustrated embodiment, the 4 bits of unique information from the original ATSC packet header are inserted into the reconstructed ATSC packet header. Next, the packet is overlaid onto the packing packet created for this particular type of packet. This ATSC transport packet (now a part of a content packet stream) is input to a super encrypt logic  105  as part of the content data stream. 
     The super encrypt logic  105  encrypts the digital content  103  using a secret (key) preferably known to the super encrypt logic  105  and a super decrypt logic  141  in the conditional access module  140 . Thus, the content is protected as it travels across a first interface  110 . The super encrypt logic  105  preferably stores multiple keys which allow the transmission of a super encrypted content data stream on a communication line  180  to multiple receivers  120  and their associated conditional access modules  140 . The content may be encrypted by any encryption algorithm including but not limited to Triple DES, DES, IDEA, or SKIPJACK. It should be noted that it is possible to pass data through the super encrypt logic  105  without encrypting it. A decision as to whether to encrypt data may be provided by instructions, for example instructions contained within the digital content  103 , or may be received from a backend  170 . The super encrypt logic  105  is controlled by the source control logic  109 . 
     A modem  106  is utilized to communicate to the conditional access module  140  through the receiver  120 . The modem  106  is used to keep the source  100  informed regarding the state of the conditional access module  140  and may also be used to pass information between the source  100  and the rest of the system. The modem  106 , which is preferably controlled by the source control logic  109 , may alternatively be replaced by various communications devices well known in the art. 
     In the illustrated embodiment, a modem switch  108  switches a modem  121 , located in the receiver  120  between ports A and B. Port A connects the modem  121  to the modem  106  located on the source  100 . Port B connects the modem  121  to the backend  170 . The backend  170  is typically located remotely from the source  100 . Typically, connection via port B connects modem  121  to the backend  170  through a telecommunications network, (e.g. a telephone company modem, a direct modem to modem connection, or a connection through an Internet Service Provider (“ISP”)). The source control logic  109  controls the position of modem switch  108 . The default position of the modem switch  108  connects the modem  121  via port B to the backend  170  except when the source  100  requires access to the receiver  120 , e.g. to communicate with the conditional access module  140 . Other configurations of the switch may, for example, connect the modem  106  to the backend  170 . 
     Operation of and communications with the source  100  is preferably controlled by the source control logic  109 . The source control logic  109  receives data from the transport packet generation device  104  and pointers, which point to the beginning of frames for use in various operational modes. 
     The first interface  110  preferably contains communications lines between the source  100  and receiver  120 . The primary communication line through the first interface  110  connects the super encrypt logic  105  to the super decrypt logic  141 , (the latter preferably being provided on the conditional access module  140 ), passing via a second interface  130  to the receiver  120  and the conditional access module  140 . The first communications line  180 , which connects between the first and second interfaces,  110  and  130  respectively, may comprise an 8/VSB or 16/VSB interface. The communication line  180  transports the modified ATSC transport packets from the source  100  to the conditional access module  140 . The 8/VSB or 16/VSB interface may be replaced with a fast digital bi-directional interface capable of handling both video and commands. As an example, an IEEE 1394 interface could combine both the VSB and modem lines. A second communications line  183  connects the modem switch  108  to the modem  121 . 
     Digital content  103  is arranged to fit into the bandwidth limitation of the modified transport packet stream. The illustrated embodiment, preferably maintains a 19.39 Mbps transport package throughput. Preferably, other content may be sent on the transport package stream by lowering the bandwidth available for the video and audio content, and using the extra bandwidth to transport other content, e.g. commands and sub pictures. 
     The receiver  120 , sometimes referred to as a set top box, may receive content from any source  100 . 
     The modem  121 , located in the receiver  120 , provides a communication link between the conditional access module  140  and depending upon the position of the modem switch  108 , the source  100  or the backend  170 . Data communicated over through modem  121  includes information relating to the state of the conditional access module  140 , and feedback data to a communication and control logic  144  from the source control logic  109 . 
     The backend  170  may, for example provide account and system management. Uploaded information may include any or all of the following: content key information used to enable content decryption, super encryption/decryption key information used to enable the super encryption functionality, interface encryption/decryption key information used to enable the interface protection functionality, play window data for specific digital content or title tables. The title tables may include data such as watermark identification, conditional access keys for a content decrypt logic  142 , and play authorization data. This communication link may also be used to download play journals, system statistics, data, etc. 
     An interface decryption logic  123 , decrypts the data stream returned from the conditional access module  140  to the receiver  120  for further processing by a transport packet demultiplexer logic  124  and a content decoder  125  before being sent to a monitor  160 . The interface decryption logic  123  uses a shared secret between itself an interface encryption logic  146  to perform decryption. The decryption algorithm used corresponds to the encryption algorithm used in the interface encryption logic  146 . This shared secret may be generated by any known technique or may be generated by a technique disclosed in copending and commonly assigned application Ser. No. 09/252,013. 
     A receiver control logic  126  controls the operation of the receiver  120 , including the modem  121 , the interface decrypt logic  123 , the transport packet demultiplexer  124  and the content decoder  125 . The receiver control logic  123  communicates with the conditional access module  120  through the second interface  130  and to the source  100  via the first interface  110 . 
     The transport packet demultiplexer logic  124  converts the transport packet data stream into elementary data packets which for example includes video, audio, and control data. Video and audio elementary data packets are forwarded to the content decoder  125 . The rest of the packets (such as control packets) are forwarded to the receiver control logic  123 . 
     The content decoder  125  decodes the digital content, now formatted in a digital content data stream (such as MPEG), into a form that may be utilized by an output device  160  to present the content to a viewer. In this embodiment, the content is preferably converted into an analog signal by known techniques. As should be recognized by those skilled in the art, different monitors may require different signal forms. For example, a digital signal may be provided for an LCD or plasma display, whereas an analog signal might be more efficient for a conventional CRT. The content decoder  125  may dynamically handle different types of coded content, e.g. MPEG and AC-3. 
     The second interface  130  provides a signal path between the conditional access module  140  and the receiver  120 . The signals that cross this interface preferably include super encrypted digital content between the super encryption logic  105  and the super decryption logic  141 , command, control, and authorization data between the modem  121  and a communication and control logic  144 , interface encrypted digital content between interface encryption logic  146  and an interface decryption logic  122  and authorization data between a copy protection and playback control logic  145  and a watermark logic  164  in the output device  160 . 
     The conditional access module  140  may be a renewable device, having logic to analyze the system and the content  103  in order to determine whether the content  103  may be displayed. By renewable, we mean that the conditional access module may be updated by either replacing the device and/or secrets used by the conditional access module and preferably reestablish pairing relationships between the conditional access module and the other devices in the system. The conditional access module  140  may also contain logic to prevent the content  103  from being displayed, logic to log system operations, etc. The conditional access module  140  may include the communications and control logic  144 , the super decryption logic  141 , content decryption logic  142 , fingerprint logic  143 , the interface encryption logic  146 , and the copy protection and playback control logic  145 . Each of these elements will be discussed below. 
     The super decryption logic  141  uses a shared secret between itself and the super encryption logic  105  to decrypt the super encrypted transport packets encrypted by the super encryption logic  105 . The content decryption logic  142  uses a secret key provided by the backend  170  to decrypt the content  103 , which was encrypted at the time it was authored utilizing the corresponding secret key. The interface encryption logic  146  uses a shared secret between itself and the interface decryption logic  122  to encrypt the transport packets for transport over the second interface  130  to the interface decryption logic  122 . The purpose of this re-encryption is to protect the transport packets as they travel over the second interface  130  where the packets may be exposed to third parties. The encryption algorithm used may be any known encryption algorithm such as DES, Triple DES, or an algorithm disclosed in copending and commonly assigned application Ser. No. 09/252,013. 
     The fingerprint logic  143  adds watermarks to the output signal of the interface encryption logic  146 . The watermark is embedded into the digital content and provides tracing information about a particular use, or an instance of the content being placed into a multimedia signal. Preferably the fingerprint information is hard to detect, hard to remove, and resistant to collusion. Some exemplary identifying information about the play session includes, but is not limited to, time of access, serial number of the content being viewed, source  100  identification data, receiver  120  identification data, conditional access module  140  identification data, and output device  160  identification data. The fingerprint logic  143  preferably uses known techniques to embed the watermark into the content  103 . 
     The protection and playback control logic  145  compares the watermark data detected from the content display stream by a watermark logic  164  for the output device  160  with data which indicates what the appropriate watermark should be for the digital content  103  currently being played. The protection and playback control logic  145  sends a message back to the watermark logic  164  as to whether to disable a display  161  in the output device  160 , hence providing a mechanism to prevent unauthorized viewing of the content  103 . The message must have enough information for the watermark logic  164  to verify the message. The message may be verified using any verification function; for example a hash function utilizing a shared secret between the protection and playback control logic  145  and the watermark Logic  164 , as described in copending, commonly assigned application Ser. No. 09/252,013, or a digital signature. 
     The blocks in the conditional access module  140  are preferably controlled by the communications and control logic  144 . The communications and control logic  144  also handles communication between the conditional access module  140  and the source  100 , including communications regarding the status of the conditional access module  140  sent back to the source  100 , and user interactions and control of system functions. The communications and control logic  144  also handles communications between the conditional access module  140  and the backend  170 , including updating title tables, updating keys, updating watermark identification, and downloading transaction and system data. 
     A third Interface  150  transports video data, audio data, and authorization data from the receiver  120  to the output device  160 . The authorization data is preferably transported between the copy protection and playback control logic  145  typically in the conditional access module  140 , and the watermark logic  164  in the output device  160 . This link facilitates an important copy protection mechanism utilized in this system architecture. Validation data is transported back and forth over this link whereby a decision may be made by the watermark logic  164  as to whether to allow the content  103  to be displayed on the display  161 . 
     The output device  160  receives a display stream from the receiver  120 , retrieves watermark data from the display stream and, in conjunction with the copy protection and playback control logic  145 , decides whether the content may be displayed. If the decision is affirmative, then the content  103  is enabled for the display  161 . This process may be performed regularly throughout the viewing of the content  103 . The output device  160  typically includes the display  161 , a display enable  162 , the fingerprint logic  163 , the watermark logic  164 , and a video logic  165 . 
     The display  161  may be any video display device (e.g., a CRT, a plasma display device, a projection display device, or an LCD display device). The display enable logic  162  inputs a signal from the watermark logic  164  and enables or disables the output of the display  161  appropriately. Fingerprint logic  163  embeds identifying information into the display signal similar to the fingerprint Logic  143 . It may be advantageous to add other identifying information related to the output device  160  in addition to the information described in the description of the fingerprint logic  143 . The watermark logic  164  removes watermarks that were embedded in the content  103 . Each time it identifies new watermark data, this information is relayed to the copy protection and playback control logic  145  for analysis. Feedback is then returned from the copy protection and playback control  145  about the validity of the content stream for presentation on the display  161 . A signal is then sent to the display enable logic  162  to disable or enable the display  161 . If no changes occur in the watermark data for more than a defined period of time, the watermark logic  164  may ask for fresh authentication. The watermark logic  164  is preferably paired with the copy protection and playback control logic  145  and verifies the authorized message from the copy protection and playback control  145 . 
     The video logic  165  receives the display stream over a communications line  182  from the content decoder  125  and passes a copy of the display content stream to the watermark logic  164 , and the fingerprint logic  163 . The video logic  165  converts the decoded content data into a content signal that may be used by the display  161 . 
     The backend  170  for the system is usually located remotely from the rest of the system. It preferably includes physical data processing equipment, communications links, and software systems. The backend  170  provides functions that include, but are not limited to, account management, content access, encryption/decryption pairing assistance, and uploading to the system, title keys, watermarks, and data required for content access. Data required for content access preferably include recalled content, prices, release dates, promotions, and downloads from the system such as content access journals and system journals. 
     As used herein, the term “data stream” refers to a continuous or semi-continuous flow of data that is moving through the system. It is convenient to label these streams to assist in understanding the flow of data through the system. Although data may travel through the system, it is the collection of data that comprises the data stream and not the hardware per se. Typically, there are several data streams in the system. They preferably include a super-encrypted content data stream (which may be found on the communications line  180 ), a watermark authorization stream (which may be found on the communications line  181 ), a content display stream (which may be found on the communications line  182 ), a receiver back channel data stream (which may be found on the communications line  183 ), a conditional access module back channel data stream (which may be found on the communications line  184 ), an interface stream (which may be found on the communications line  185 ), a backend data stream (which may be found on the communications line  186 ), unencrypted content stream (which may be found on the communications line  187 ), and a receiver/CAM control stream (which may be found on the communications line  188 ). 
     The super encrypted content data stream which contains super encrypted content data is transported over communications line  180  to the receiver  120  and the conditional access module  140  from the super encrypt logic  105  on the source  100 . This data stream does not always have to be super encrypted. The super encrypt logic  105  may be enabled or disabled by the source control logic  109 . When the super encrypt logic  105  is disabled, the data stream from transport packet generation logic  104  will preferably pass through super encrypt logic  105  without any modification. 
     An authorization data stream is transported over communications line  181  which connects the watermark logic  164  in the output device  160  and the copy protection and playback control logic  145  in the conditional access module  140  over the second interface  130  and the third interface  150 . Information relating to authorizing the display of content  103  on the output device  160  is communicated in this data stream. 
     The communications line  182  transports the content display stream from the content decoder logic  125  on the receiver  120  to the video logic  165  on the output device  160  over the third interface  150 . This data stream carries the decoded content for display on the output device  160 . 
     Two of the data streams comprise a back channel for this system, a receiver back channel data stream is (which may be found on the communications line  183 ) and a CAM back channel data stream (which may be found on the communications line  184 ). The communications line  183  transports the receiver back channel data stream from the modem  121  on the receiver  120  to the modem switch  108  on the source  100  over the first interface  110 . The communications line  184  carrying the CAM Back channel data stream connects the communications and control logic  144  on the conditional access module  140  to the modem  121  on the receiver  120  over the second interface  130 . These data streams provides a channel for the conditional access module  140  and the receiver  120  to communicate their state and other information to the source  100  and the backend  170 . 
     The interface data stream (which may be found on communications line  185 ) carries a freshly encrypted version of the content after the conditional access module has otherwise processed it from the interface encrypt logic  146  on the conditional access module  140  to the interface decrypt logic  123  on the receiver  120  over the third interface  130 . This fresh encryption of the content protects the content while being transported over the second interface  130  where it could be compromised. 
     The communications line  186  transports a backend data stream between the backend  170  and the system through the modem switch  108  on the source  100  over the fourth interface  172 . 
     All data that comes from the source  100  does not need to be encrypted. The unencrypted content stream (which may be found on communications line  187 ) provides a shortcut for the digital content stream to proceed directly to the transport packet demultiplexer  124 . In the cases where the content is not encrypted and no protection is needed for the digital content  103 , the pathway through the conditional access module may be bypassed. The transport packet demultiplexer logic  124  may easily determine if the unencrypted content stream (which may be found on communications line  187 ) is in fact unencrypted. If the content data stream (which may be found on communications line  187 ) is unencrypted, then the transport packet demultiplexer logic  124  will process data from this stream rather than the data coming from the interface decrypt logic  123 . 
     The receiver/CAM control stream (which may be found on communications line  188 ) provides a communications channel for the conditional access module  140  to communicate with the receiver  120 . Information that two subsystems might share could include status data, synchronization data, and control data. 
     Referring now to  FIG. 2 , which is a flow diagram of the watermark logic  164  shown on  FIG. 1 , there is depicted an exemplary logic (which includes analysis of the watermark contained in the content) used to determine if the output device  160  should or should not be enabled. 
     At step S 202  the watermark logic  164  initializes the monitor  161  to an enabled state by sending an enable signal to the monitor enable logic  162 . Content  103  is received from the video logic  164  at step S 204 . The watermark is removed from the video content at step S 206 . Next, the watermark that was just removed from the video content is compared to a predetermined watermark which, may be a previous watermark, at step S 208 . If the watermarks are the same, the content is authorized for viewing and the display  161  is enabled at step S 218 . In essence, this step is detecting a change in the watermark. If the watermark has changed, then a copy of it is sent to the protection and playback control logic  145  in the conditional access module  140  for authorization at step S 210 . At step S 212 , the watermark logic  164  waits for a response from the copy protection and playback control logic  145 . If the response has timed out (step S 214 ), then the display is disabled at S 220 . Otherwise control passes to step S 216  where the response is analyzed to see if the content is authorized for viewing. If the content is authorized for viewing, then the display  161  is enabled at step S 218 . If the content is not authorized for viewing, then the display  161  is disabled at step S 220 . Control then returns to step S 204  where the process starts again. 
       FIG. 3  depicts the creation of a single exemplary ATSC transport packet stream which combines several different display streams, in essence creating virtual streams. This process takes place as part of the disc authoring process. Authored content  103  may have multiple streams. There may be several types of streams including but not limited to audio and video. Each stream type may have multiple streams. Examples include multiple video angles, multiple languages, and different rating cuts. 
     Blocks  300 ,  301  and  302  represent n virtual video streams for a channel i. The display stream for virtual video channel 1, option 1 is Vi, 1  300 . The display stream for virtual video channel 1, option 2 is Vi,2  301 . The display stream for virtual video channel 1, option n is Vi,n  302 , where n may be any value between 1 and the maximum number of choices available for this virtual video stream. 
     The video virtual stream former  303  accepts as input all of the possible video display streams that need to be recorded on content  103 . The video virtual stream former  303  combines these streams into one continuous ATSC stream. Information identifying which stream each packet originated from is stored in packet headers. The resultant stream is Vi  304 . The 
     Blocks  305 ,  306  and  307  represent n virtual audio streams for a channel j. The display stream for virtual audio channel 1, option 1 is Vj,1  305 . The display stream for virtual audio channel 1, option 2 is Vj,2  306 . The display stream for virtual audio channel 1, option n is Vj,m  302 , where m may be any value between 1 and the maximum number of choices available for this virtual audio stream. 
     The audio virtual stream former  307  accepts as input all of the possible audio streams that need to be recorded on content  103 . The audio virtual stream former  307  combines these streams into one continuous ATSC stream. Information Identifying which stream each packet originated from is stored in packet headers. The resultant stream is shown as Vj  309 . 
       FIG. 4  depicts an example of an ATSC transport packet stream, grouped and packed into DVD sectors. In this example the ATSC transport packet stream consists of packets for two video streams and two audio streams. In the preferred embodiment, each DVD sector will only contain ATSC packets of a particular display stream. There may be several display streams for each type of packet. 
     Each packet in the ATSC transport packet stream  400  is preferably processed sequentially, as follows. The packet header is analyzed to determine which stream the corresponding packets come from. The packet is then packed into a DVD sector reserved for only packets of the type matching this packet. For example, six V1 packets in ATSC transport packet stream  400  may fit in and are packed into DVD sector  401 . After ATSC transport packet stream  400  is filled, the next V1 packet will be packed into DVD sector  405 , and so on. In this example the same process takes place for the A1, A2, and V2 packets. Provisions may be made for packing packets across sector boundaries, by storing enough information in the sector headers to restore the packets. Such information may only need to be a flag to indicate that the first packet of data in a sector is fractional. The system may then concatenate this packet to the last packet of this type received when reconstructing the stream later. 
       FIG. 5  depicts exemplary audio and video streams laid out on a DVD disc. In this example, the DVD sectors  450  contain packets of only one stream each. Sectors  501 ,  502 ,  503 ,  513 ,  514 , and  515  contain packets for a first video stream. Sectors  507 ,  508 , and  509  contain packets for a second video stream. Sectors  504 ,  505  and  506  contain packets for a first audio stream. Sectors  510 ,  511  and  512  contain packets for a second audio stream. The packets may be laid on the disc in any order, but for efficiency&#39;s sake, they are usually laid out in as close an order to their likely access as possible. 
     The optical disc may be authoring as follows. The disc may contain several elementary streams that may include but are not limited to elementary audio and elementary video streams. Multiple streams may exist for each of the elementary stream types. The content from these elementary streams is converted to standard ATSC transport packet streams. A virtual stream is created as shown in  FIG. 3  for each stream type which combines all of the multiple streams of that type. The virtual streams are then multiplexed together into one ATSC transport packet stream  400 . The ATSC transport packet stream  400  is grouped into DVD sectors  450  as shown in  FIG. 4 , including the case of padding packets. The ATSC transport packets may be modified utilizing common well-known compression algorithms to reduce their size. 
     A sector header is created. Four bits of unique information from the ATSC packet header are saved for insertion into the DVD-sector header for use during reconstruction. These four bits include 2 transport_scrambling_control bits and two adaption_field_control bits. The four-byte header from the ATSC transport packet may now be discarded as well as padding packets. Information required to restore the ATSC packet stream, including padding packets, is saved for insertion into the DVD sector headers. 
     Next, the modified ATSC transport packets are packed into the DVD sectors, utilizing an ATSC to DVD grouping algorithms.  FIG. 4  shows an example of ATSC transport packets being grouped into DVD Sectors. In our preferred embodiment, each sector may only carry one type of data corresponding to the ATSC transport packet types. Sector packet types may include but are not limited to video or audio packets. 
     The sector header will carry information to assist the reconstruction of the original ATSC transport packets. This information may include but is not limited to pointers to packets which contains the beginning of a frame, pointers to the beginning of a fractional packet, location data for audio and video packets, the number of packets packed into this frame, the sector type identifier, and unique ATSC packet header data. 
     The DVD data sectors then are laid out for recording on the media. The layout process should optimize the sectors to produce efficient access of the content. 
     The present invention provides a series of security features to adequately protect the transmission of content data from a source device to a display device. The security features include pairing, super-encryption and re-encryption, interface protection, pirate card rejection, watermark detection and authorization request by the monitor, key management and registration, disc/title integrity data, and utilization of a new HD-DVD disc structure. 
     A device A is paired to a device B if device B is authorized to effectively communicate with device A. Possible pairs utilized in this system include conditional access module  140  to source  100 , receiver  120  to conditional access module  140 , and conditional access module  140  to monitor  160 . Pairing is extensively utilized in this architecture to ensure that a predetermined flow of data and authorization is maintained, and that all of the hardware elements are in fact the intended hardware elements to be in this system. 
     Interface protection techniques are used to protect content while traveling across the first interface  110 , the second interface  130 , or the third interface  150 . Super-encryption and re-encryption are utilized as a technique to protect the encrypted content as it is transported from the source  100 , across the first interface  110  and the second interface  130 , to the conditional access module  140 . The encrypted content is encrypted again using a secret known only to the super encrypt logic  105  and super decrypt logic  141 , in the case that the conditional access key used to encrypt the digital content  103  has been compromised. Again, the encryption may be any type of encryption including DES and triple DES. 
     Pirate Card Rejection techniques are also used, wherein several factors may cause the system to reject the conditional access module  140  as an authorization device. An example includes title based rejections where the conditional access module  140  must prove its identity to the system based on a title by title basis. Another example includes rejection because the conditional access module was not authorized to communicate in the system. 
     Watermark detection and authorization request by the output device  160  is another protection mechanism utilized in this system. A content data stream  182  is generated by a content decoder  125 . This content decoder may be an MPEG decoder or some variant. Data is transported to the watermark logic  164  through the video logic  165 . The watermark logic pulls out the watermark data from the data content stream and compares the watermark data to see if watermark data has changed from the last authorized watermark or if a timeout period has occurred. If either case has happened, then the watermark logic  164  requests a new authorization from the copy protection and playback control logic  145  to enable the display  161 . 
     The following is a discussion of Conditional Access and Interface Protection utilized in this architecture. The security architecture utilizes a bi-directional communications path between the source  100  and the receiver  120 . In particular, use is made of the path from the conditional access module  140  to the source  100  in order to strengthen the pirate-card-rejection verifier functionality. The conditional access module  140  is accessed while present in a card-slot of the receiver  120  during communications between the source  100  and conditional access module  140 , communications between the conditional access module  140  and receiver  120 , and communications between the conditional access module  140  and the backend  170 . It is the responsibility of the backend  170  to reconcile charges. In particular, conditional access modules  140  associated with different receiver devices  120  do not directly communicate. 
     A conditional access module  140  to source  100  pairing provides for a means of distributing a long-term shared secret value secret to the source  100  and conditional access module  140 . The one-way pairing authenticates the conditional access module  140  to the source  100 . The conditional access module  140  will accept content regardless of origin. The conditional access module  140  to source  100  pairing provides for pirate card rejection in that a compliant source  100  will not effectively communicate with a conditional access module  140  which is not in possession of the long-term shared secret value. This is accomplished through implicit authentication since only the designated conditional access module  140  has the capability of deriving the session key from the long-term shared secret value, where the session key is used to super-encrypt the digital content  103 . More specifically, a key may be used to encrypt the encrypted digital content  103  that results from processing the plaintext content data under the conditional access (CA) key. The session keys may derive freshness from counter values provided to the conditional access module  140  in the clear by the source  100 . There is no need for the conditional access module  140  to provide freshness to the source  100 , since replay of the super-encrypted content  103  to the conditional access module  140  would result in additional logging. 
     The super-encryption mechanism employed by the source  100  also provides for interface protection of the encrypted digital content  103 , which could otherwise be decrypted using a pirate apparatus which makes use of the universal key present in all legitimate conditional access modules  140 . 
     As a further layer of protection, to ensure that the use of digital content  103  is logged by the conditional access module  140  at least once as a condition of playback, the Title ID information may be transmitted (assuming that it is otherwise permitted) by the source  100 , where the source  100  may require an authenticated receipt of the Title ID information from the conditional access module  140  prior to transmission of the (super-encrypted) digital content  103 . The receipt may be freshly authenticated by the conditional access module  140 , for subsequent verification by the source  100 , using a most recent counter value provided by the source  100 . Although the authentication mechanism and the session keys may both based on the long-term shared secret value, the authentication may be cryptographically stronger because it ultimately uses a significantly longer key. 
     The receiver  120  may supply freshness to the conditional access module  140  in order to prevent effective replay of the content data  103  from the conditional access module  140  to the receiver  120 . The conditional access module  140  encrypts the plaintext content  103  read from the optical disc using a session key negotiated between the conditional access module  140  and receiver  120 . The session key computation may derive freshness from a counter value provided by the receiver  120 . A receiver  120  to conditional access module  140  pairing provides for a means of distributing a long-term shared secret value to the conditional access module  140  and receiver  120 . The receiver  120  to conditional access module  140  pairing provides for implicit authentication by ensuring that only the designated receiver  120  will be able to derive the session key by means of possession of the long-term secret. This one-way pairing authenticates the receiver  120  to the conditional access module  140 . The receiver  120  may accept content for decryption regardless of origin. 
     Session keys may be derived through any number of techniques known to those in the art. For example, a single-DES session keys could be derived by computing Hash56(counter | | shared secret value | | counter); and (in the case of communications between the source  100  and the conditional access module  140 ) authenticated receipts may be formed by Hash96(message | | Hash64(counter | | shared secret value | | counter)) ⊕ Hash96(counter | | shared secret value | | counter), where the counter value is incremented by one between the computation of authenticated receipts and session keys. Hash56( ) may be derived by extracting the 56 least significant bits of a 160-bit hash word, Hash64( ) may be derived by extracting the 64 least significant bits of the hash word, and Hash96( ) may be derived by extracting the 96 most significant bits of the hash word. | | denotes concatenation of bit-streams, and ⊕ denotes the bit-wise exclusive-or operation. 
     The conditional access module  140  to source  100  pairing may be achieved as follows. In order to effect the pairing between the conditional access module  140  and the source  100 , the backend  170  could issue a certificate binding the source ID to the Diffie-Hellman public key of the conditional access module  140 , gXcam. The Diffie-Hellman public key of the source  100 , gXplayer, need not be authenticated. If the certificate verifies correctly, and the player ID within the certificate matches the ID of the source, the player sets the long-term shared secret value to the 256 least significant bits of the Diffie-Hellman value computed using gXcam and Xplayer, namely (gXcam)Xplayer=gXcam*Xplayer. The session keys may be computed based on the long-term shared secret value. The player&#39;s Diffie-Hellman key pair and source ID may be established during the manufacturing process or may be generated in the source  100  using suitable randomness. A source ID may be used by the source  100  to determine whether it is authorized to communicate with the conditional access module  140 , and thus could be chosen so as to be very unlikely to coincide with the IDs of other sources. 
     The receiver  120  to conditional access module  140  pairing may be achieved as follows. In order to effect the pairing between the conditional access module  140  and the receiver  120 , the receiver  120  may transmit to the conditional access module  140  the certified Diffie-Hellman public key, gXfinal of the receiver devices  120 , and the conditional access module  140  may transmit to the receiver  120  the unauthenticated Diffie-Hellman public key, gXcam of the conditional access module  140 . The certificate may be verified by the conditional access module  140  using the appropriate chain of certified keys. If this certificate verifies correctly, the conditional access module  140  may use its private Diffie-Hellman key Xcam in conjunction with gXfinal in order to compute the Diffie-Hellman value (gXfinal)Xcam=gXfinal*Xcam. As the credential confirmation step, the most significant 256 bits of this value may be checked for a match against the 256 bits transmitted to the conditional access module  140  by the receiver  120  (after the conditional access module  140  transmits gXcam to the receiver  120 . If the two 256-bit blocks match, the conditional access module  140  may set the long-term shared secret value held by it with the receiver  120  to the 256 least significant bits of the Diffie-Hellman value gXfinal*Xcam. The certificate and evidence-of-compliance block of the receiver device&#39;s  120  gXfinal may be sent (authenticated by the conditional access module  140  to the backend  170 . The session keys and authenticated receipts may be computed based on the long-term shared secret value with the receiver  120 . The next section explains, in particular, the generation procedure for Xfinal. 
     One skilled in the art will appreciate that registration and certification techniques may also be used in this system to enable the authentication of an individual receiver  120  and to enable clone detection. This will enable confirmation that each receiver  120  was built with the consent of the licenser, without unnecessarily exposing secrets held by the receiver  120 . Therefore, we have the following four goals: clone detection, unit-by-unit licensing, manufacturer accountability over licensed units, and limited manufacturer and licenser responsibility for receiver  120  secrets. 
     We also do not assume that the receiver  120  has a good random number generator, in that we make productive use of such randomness but ensure that an acceptable level of security is preserved even if such randomness maynot be relied upon for strength. 
     Although there may be a single licensing authority, there may be many licensed competing receiver  120  manufacturers, and customers may have access to many service providers, all of who may have no reason to trust one another. For example, a receiver  120  should be able to move between service providers without introducing trust dependencies between those providers. 
     A clone device may be defined as either an exact copy of a manufactured receiver  120  or built from the keying material the licenser gave the manufacturer for that device. Unit-by-unit licensing requires that the licensers produce and distribute the secrets to be held by the receiver  120 . Limited manufacturer and licenser responsibility for these secrets requires that the secrets be placed in the receiver  120  not be valid forever in the sense that knowledge of these secrets is not sufficient to compromise compliant receivers  120 . Eliminating trust dependencies between service providers requires that service providers not know receiver  120  keys, and therefore that public-key cryptography is used. 
     Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. For example, it will be apparent to those of skill in the art that the content may be provided from any type of source device which may produce content which may be encrypted according to principles of the present invention. Therefore, unless such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.