Abstract:
According to the invention, a method for protecting digital television from unauthorized digital receivers within a population of digital receivers is disclosed. Each digital receiver in the population has a unique identifier. In one step, provisioning information is received from a subset of the population of digital receivers indicating that the subset is potentially within range to receive digital television from a broadcaster. First decryption information is distributed to the subset of the population of digital receivers. The first decryption information allows for potentially decrypting a plurality of programs coextensively in time. The unauthorized digital receivers are cryptographically excluded from using the first decryption information. A first program is encrypted using a first method that is cryptographically related to second decryption information. The first program is sent. The second decryption information is distributed and cryptographically secured with the first decryption information.

Description:
This application claims the benefit of and is non-provisional of U.S. Provisional Application Ser. No. 60/405,454 filed on Aug. 23, 2002, which is incorporated by reference in its entirety. 

   BACKGROUND OF THE INVENTION 
   This invention relates in general to copy protection and, more specifically, to copy protection of terrestrial broadcast digital television. 
   Copy protection and digital rights management (DRM) are used to protect content from use not licensed by the copyright holder. There are various levels of protection which include copy freely, copy once, copy never, etc. Protection of movies and music on the Internet has been performed with DRM. In some cases, software is also protected with DRM. 
   Digital television (DTV) is broadcast in many designated marketing areas (DMA). One popular type of DTV is high-definition television (HDTV). Some televisions include DTV tuners, while others rely on external tuners. Anyone with a tuner can receive and view the broadcast programs. These broadcasts are transmitted in the clear, but may include a flag that indicates the program should not be copied. The flag is also in the clear, but is intended to secure the program. A properly-functioning DTV tuning device recognizes the flag and prevents copying to the extent possible. Those skilled in the art can appreciate that the flag could easily be replaced by a content pirate to make the program unsecured. Conventional DTV is referred to as unprotected DTV in this application. Further, many other techniques can be used to pirate or steal the broadcast programs. 
   In the United States alone there are hundreds of millions of TV sets that may move to various geographic locations during their lifetime. Today, most of these TVs are analog, but the trend is toward use of TVs and external tuners that can receive unprotected DTV. A given broadcaster in a particular DMA only needs to worry about those TVs that can receive the signal, but the owners can move from one DMA to another DMA along with his or her TV. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is described in conjunction with the appended figures: 
       FIG. 1A  is a block diagram of an embodiment of a terrestrial broadcast system; 
       FIG. 1B  is a block diagram of another embodiment of the terrestrial broadcast system that provisions centrally; 
       FIG. 1C  is a block diagram of yet another embodiment of the terrestrial broadcast system that allows for sibling content broadcasters to share provisioning information; 
       FIG. 1D  is a block diagram of still another embodiment of the terrestrial broadcast system that provisions centrally without maintaining a central receiver database; 
       FIG. 1E  is a block diagram of yet another embodiment of the terrestrial broadcast system that shares a local receiver database; 
       FIG. 2A  is a protocol flow diagram of an embodiment of provisioning and key distribution process that uses central provisioning; 
       FIG. 2B  is a protocol flow diagram of another embodiment of provisioning and key distribution process that allows sibling content broadcasters to share provisioning information; 
       FIG. 2C  is a protocol flow diagram of yet another embodiment of provisioning and key distribution process that sends content keys for a number of content broadcasters; 
       FIG. 2D  is a protocol flow diagram of still another embodiment of provisioning and key distribution process that sends content keys for use with a number of content broadcasters; 
       FIG. 3  is a flow diagram of an embodiment of a process for management of digital receivers in the terrestrial broadcast system; and 
       FIG. 4  is a flow diagram of an embodiment of a process for managing cryptographic functions with the digital receiver. 
   

   In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The ensuing description provides preferred exemplary embodiment(s) only, and is not intended to limit the scope, applicability or configuration of the invention. Rather, the ensuing description of the preferred exemplary embodiment(s) will provide those skilled in the art with an enabling description for implementing a preferred exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the invention as set forth in the appended claims. 
   Referring initially to  FIG. 1A , a block diagram of an embodiment of a terrestrial broadcast system  100 - 1  is shown that distributes protected DTV. This embodiment shows only two content broadcasters  104  and four digital receivers, but it is to be understood that other embodiments could have tens of content broadcasters  104  and hundreds of thousands of digital receivers  126  or more. For example, a city having a population of a million could expect twenty content broadcasters  104  and a million digital receivers. 
   Content broadcasters  104  transmit programming by way of terrestrial antennas  124  in digital format. Digital receivers  126  at the user locations each receive this signal with an antenna  136  and decode it for presenting on a television or other display. In this embodiment, each content broadcaster  104  can provision digital receivers  126  to be able to decode the content broadcast. In this embodiment, all digital receivers  126  that can receive the signal from the broadcaster  104  is allowed to decode that signal unless permission has been revoked. The content broadcaster in this embodiment maintains a local receiver database  116  of digital receivers  126  allowed to decode the content. Cryptographic techniques are used in this embodiment to prevent revoked receivers  126  from viewing the content. 
   This embodiment uses both local and central receiver databases  116 ,  108  to track provisioned receivers  126 . The local database  116  lists the receivers  126  allowed to receive the next revocation management message (RMM). An RMM is very similar to an Entitlement Management Message (EMM), which delivers authorization data and associated keys. Though an RMM delivers this same information, its purpose also includes the delivery of revocation information if required. Thus one important purpose is deauthorization, rather than authorization, and its name reflects this. Each provisioned receiver  126  communicates a unique serial number, a unit key and a certificate for storage in the local receiver database  116 . The unique serial number is used to track the digital receiver  126 . The certificate is recursively generated to authenticate the receiver  126  back to a root authority. For example, the unique serial number for the unit could be encrypted by a chain of trust such that checking of the certificate assures the receiver  126  is authentic. 
   The unit key is used to individually encrypt the RMM sent to each of the provisioned receivers  126 . The RMM has an expiration date and a category key used to decrypt revocation control messages (RCM). Each program or channel includes a RCM that has a content key to decrypt the program or channel. Some embodiments have a RCM for each program and others have a RCM for each channel. Only the digital receivers  126  that have a current RMM to decrypt the RCM can get the content key. De-provisioning or revocation occurs when the RMM changes and certain receivers  126  do not receive the new category key. It should be noted that there could be a number of category keys, where one or more content broadcasters share a particular category key. In this embodiment, the unit key is unique and distinct to a single receiver and is a public key using an asymmetric algorithm, such as RSA. The category and content keys are private keys using a symmetric algorithm, such as 128-bit AES, but other embodiments could use different algorithms and key lengths. 
   The central receiver database  108  has information gathered from a number of local receiver databases  116 . Entries in the local and central receiver databases  116 ,  108  are reconciled by the content broadcaster  104  through a wide area network (WAN)  120 . Once a receiver  126  is provisioned, the central receiver database  108  is informed and the data on the receiver  126  is forwarded. This information can be forwarded to other content broadcasters  104 - 2  in the designated marketing area (DMA) of the first content broadcaster  104 - 1  who originally received the provisioning. Content providers  104  in neighboring DMAs that overlap the first DMA would also be informed. All of their local databases  116  would be updated and RMMs would be sent. 
   Whenever a digital receiver  126  moved from a DMA, the local receiver databases  116  would be updated to remove the relevant entry. Some embodiments have two-way communication with the digital receivers  126  such that polling could be performed to determine when a digital receiver  126  had moved or gone out of service. In systems where the communication is one-way and the receiver  126  cannot automatically send information to the content broadcasters  104 , the moved receivers  126  could be determined by querying the central receiver database  108  to find units that have provisioned at another DMA. For digital receivers  126  that are mobile, such as those in autos, they could be provisioned nationwide by making a note in the central receiver database  108  and propagating the entry to all local receiver databases  116 . Alternatively, the user could provision once in each DMA. 
   The provisioning transport  112  provides a mechanism for new digital receivers  126  to be provisioned. This could be performed at the store that sold the digital receiver or at the user location. Some embodiments could provide temporary keys to allow viewing some terrestrial content before provisioning is required when the RMM key expires. Two-way communication between the digital receiver  126  and content broadcaster enables provisioning in an automated and/or manual fashion. 
   There are many possibilities for doing receiver  126  provisioning. In one embodiment, the store clerk performs the provisioning before the customer leaves the store. Address information from the user could be used to determine the relevant DMA for that address. The unique identifier, unit key and certificate could be communicated by an electronic connection, for example, a network connection. In some embodiments, only a unique identifier is communicated and the content broadcaster  104  queries a database for the receiver&#39;s unit key. The unit key could also serve as the unique identifier to reduce the information needed, though its secure handling might necessitate significant protections. 
   Another possibility is to use an electronic connection to the content broadcaster  104  as the provisioning transport  112  to communicate information on the digital receiver  126 . This connection could be through a cable modem, DSL modem, Ethernet, wireless networking, cellular phone network, phone modem, satellite link, or other datalink. A port on the digital receiver  126  could be connected through a network to allow providing provisioning information to the content broadcaster. This connection could be only during provisioning or a persistent connection to allow polling, RMM and RCM delivery, etc. The retailer could perform the connection at the retail location before the user took home the receiver  126 . 
   In another embodiment, the content broadcaster  104  has a list of the unit keys for all or most digital receivers  126 . The list may be in the central receiver database  108 , for example. The user could telephone in, e-mail or mail his or her unique serial number for the digital receiver  126 . The unique serial number would be used to retrieve the unit key for the digital receiver  126  for storage in the local receiver database  116 . Alternatively, the user could in some embodiments read-off the characters that make up the unit key which could serve as the unique serial number also or that could also be read-off to a customer representative on the telephone if that proves practical. 
   This embodiment has digital receivers  126  that fall into two general categories, namely, transcoders  128  and digital tuners  132 . The transcoder  128  takes the protected DTV signal, unscrambles it and recodes it for a format compatible to the display device. In many cases, the recoded format is a baseband signal, a NTSC signal, or an unprotected DTV signal. For example, the transcoder  128  could receive the protected DTV signal, unscramble it, and output it remodulated as an unprotected DTV signal. The tuner in the display decodes and presents the unprotected DTV signal for the user. Transcoders  128  are particularly useful when an original population of receivers was deployed without decryption capability, thus requiring a nearby device (i.e., a transcoder  128 ) to adapt an encrypted broadcast DTV signal to the unencrypted format they can process. 
   Some embodiments of this invention could be used in a hybrid digital broadcast system where some content is protected and some is not. The digital receiver  126  would be used for the content that is protected, while a conventional receiver would be used for content that is not encrypted. The user could view the unprotected content with the conventional receiver, but would require a digital receiver  126  to view the protected content. Revocation of the right to use the digital receiver  126  would not affect the user&#39;s ability to view the unprotected content. 
   The digital tuner  132  could be integral or separate from the display. In this embodiment, the digital tuner  132  is integral with the display such that the program is protected until it reaches the television. The digital tuner receives the protected DTV signal and unscrambles it. Unscrambling includes decryption with a key available to provisioned digital receivers  126 . 
   With reference to  FIG. 1B , a block diagram of another embodiment of the terrestrial broadcast system  100 - 2  is shown that provisions digital receivers  126  centrally. In this embodiment, the digital receivers  126  are provisioned centrally by adding the unit key, certificate and unique serial number to the central receiver database  108 . Based upon location information, the entry is propagated to the local receiver databases within likely transmission range of the digital receiver  126 . 
   Referring to  FIG. 1C , a block diagram of yet another embodiment of the terrestrial broadcast system  100 - 3  that allows for sibling content broadcasters  104  to share provisioning information without the need for a central receiver database  108 . The digital receivers  126  provision with a first content broadcaster  104 - 1 . The entry added to the first local receiver database  116 - 1  is propagated to another local receiver database  116 - 2 . Contact to geographically remote local receiver databases  116  could be performed periodically to determine those digital receivers  126  that have moved. In this embodiment, there are a number of content broadcasters  104  that share the first local receiver database  116 - 1 . These content broadcasters  104  could share the same RMM or use a number of RMMs. 
   With reference to  FIG. 1D , a block diagram of still another embodiment of the terrestrial broadcast system  100 - 4  is shown that provisions centrally without maintaining any local receiver databases  116 . In this embodiment, the provisioning is done to update the central receiver database  108 . Each entry in the central receiver database  108  can be geographically filtered by the content broadcasters  104 . When determining the RMMs to send, the content broadcaster  104  queries the central receiver database  108  for the list of provisioned digital receivers  126  within probable broadcast range. 
   Referring next to  FIG. 1E , a block diagram of yet another embodiment of the terrestrial broadcast system  100 - 5  is shown that shares a local receiver database  116  with many content broadcasters  104 . In this embodiment, all the content broadcasters  104  use a local receiver database  116 . All users who provision a digital receiver would contact a single entity for provisioning and that provisioning information is accessible to all content broadcasters  104 . Some content broadcasters  104  directly connect with the receiver database  116  and others connect over a WAN  120 . The content broadcasters  104  can use any number of category keys. 
   With reference to  FIG. 2A , a protocol flow diagram of an embodiment of provisioning and key distribution process  200 - 1  is shown that uses central provisioning. The depicted portion of the flow begins in step  202  where the first transcoder  128 - 1  sends provisioning information to the central receiver database  108  by way of the provisioning transport  112 . The certificate in the provisioning information could be validated to confirm authentication of the first transcoder  128 - 1 . In steps  206 - 1  and  206 - 2 , the provisioning information is sent to the first and second content broadcasters  104 - 1 ,  104 - 2  who are determined to be in likely broadcast range of the first transcoder  128 - 1 . Additionally, the category key(s) could be delivered by the central receiver database  108  or the content broadcasters  104  could derive their own category key(s). In this embodiment, the first and second content broadcasters  104  use different category keys. 
   In steps  210 - 1  and  210 - 2 , the unit key is taken from the provisioning information by each of the first and second content broadcasters  104 - 1 ,  104 - 2 . An RMM is created by each content broadcaster  104 . The RMM includes the category key for the content broadcaster  104  and is encrypted using the unit key for the transcoder  128 - 1 . In this embodiment, the unit key is a public key and the category key is a private AES 128-bit key. The first RMM is sent from the second content broadcaster  104 - 2  in step  212  and the second RMM is sent from the first content broadcaster  104 - 1  in step  216 . 
   In step  220 , the RMM is decrypted by the transcoder  128 - 1  using the private version of the unit key to reveal the category key for the second content provider  104 - 2 . In step  224 , a first RCM is received along with a first program from the second content provider  104 - 2 . Using the category key, the first RCM is decoded to reveal a first content key for the first program. Decrypting the program with the first content key allows producing an unprotected DTV signal for the display to process. The RMM for the first content provider  104 - 1  is received in step  216  and decoded to reveal another category key in step  228 . In step  232 , a second RCM and a second program are received from the first content provider  104 - 1  for transcoding with a second content key decoded from the second RCM. 
   In this embodiment there is a RCM for each program, but other embodiments are not so limited. For example, the RCM could designate a content broadcaster(s)  104  and a time frame. All programs from that content broadcaster  104  during that time frame would use the content key in the RCM. For example, the RCM could be valid for two hours, a day, a week, a month, a year, etc. A program may be protected by a first content key and then roll-over to the next content key during the program. 
   Referring to  FIG. 2B , a protocol flow diagram of another embodiment of provisioning and key distribution process  200 - 2  is shown that allows sibling content broadcasters to share provisioning information. Also, the first and second content broadcasters  104 - 1 ,  104 - 2  in this embodiment use the same category key and share a local receiver database  116 . The transcoder  128 - 1  provisions with the first content broadcaster  104 - 1  in step  204  to add the provisioning information to the local receiver database  116 . In step  216 , the RMM is encrypted using the public unit key of the transcoder  128 - 1 . The category key is retrieved from the RMM in step  220 . RCMs and programs from both content broadcasters  104  are decoded in steps  224  and  232 . The RCMs are unique to their respective program in this embodiment, but some embodiments could have the same RCM for more than one program. 
   This embodiment uses a single RMM for two content broadcasters  104 , but a single RMM could provide a category key for any number of content broadcasters  104  and their RCMs. For example, one embodiment could include twenty content broadcasters  104  that use a single RMM. Another embodiment could use three RMMs to cover the same twenty content broadcasters. In yet another embodiment, twenty content broadcasters  104  could have fifty content services and use fifty RMMs such that there was one for each content service. Any permutation of RMMs and content services is possible in various embodiments. 
   With reference to  FIG. 2C , a protocol flow diagram  200 - 3  of yet another embodiment of provisioning and key distribution process is shown that sends content keys for a number of content broadcasters  104 . This embodiment does not use a category key or RMM to deliver it. The RCM is uniquely encrypted for each receiver  126  with the unit key for that unit and sent from each content broadcaster in steps  240  and  248 . Using the unit key, either symmetric or asymmetric decryption could be performed to derive the content key from the RCM in steps  244  or  252 . In step  246 , a first program is received from the second content broadcaster  104 - 1  for decryption with the first content key. The content key could be valid for a single program or a time period, for example, a number of hours, a day, a week, a year, etc. 
   In some embodiments, multiple content services are provided to the user by a content broadcaster  104 . In other words, a given content broadcaster  104  may have one or more content services. From the user&#39;s perspective, a content service is a channel of video or audio programming or an on-demand video service. In the various embodiments, there may be any number of category or any number of content keys associated with a content broadcaster  104 . For example, a content broadcaster  104  may offer thee services, but have only two different key schemes. Two of the services could have only a RCM for each service and not use an RMM, while another service could use both a RMM and RCM to enable the user to play the content service. 
   Referring next to  FIG. 2D , a protocol flow diagram  200 - 4  of still another embodiment of provisioning and key distribution process is shown that sends content keys for use with a number of content broadcasters  104 . This embodiment does not use a RMM message, but uniquely encrypts the RCM message using the unit key for each receiver  126 . The content key revealed from the RCM in step  264  is used to decrypt a first program from a second content broadcaster  104 - 2  in step  272  and decrypt a second program from a first content broadcaster  104 - 1  in step  276 . 
   There are many variations on the number of content keys for a given implementation. The embodiment of  FIG. 2C  uses a content key for each content broadcaster  104 . Some embodiments could have a number of content keys for the various services of a content broadcaster  104 . With the embodiment of  FIG. 2D , a content key is used for all content broadcasters  104 , but other embodiments could use a content key for less than all content broadcasters  104 . For example, there might be four content keys used among twenty content broadcasters. For embodiments that don&#39;t use a RMM, revocation of the right to use received program is performed by not sending a new RCM that is uniquely encrypted for the receiver  126 . Once the old content key expires, a new RCM is not provided such that the right to use the content expires with the old content key. 
   The embodiments of  FIGS. 2C and 2D  do not use a RMM, but other embodiments could instead not have a RCM. The RMM is uniquely encrypted for the user and protects a category key. In this embodiment, that category key is used to decrypt programs from one or more content broadcasters  104  or services. Changing the category key without sending a RMM to a unit would revoke the right for that unit to use the content service(s) using the new category key. 
   With reference to  FIG. 3 , a flow diagram of an embodiment of a process  300  for management of digital receivers  126  in the terrestrial broadcast system  100  is shown. By changing the category key without providing some digital receivers  126  the new RMM, those digital receivers  126  can have their provisioning effectively revoked. This is a much more effective method than traditional distribution of Certificate Revocation Lists (CRLs), which can be blocked. The depicted portion of the process begins in step  304  where provisioning information is received from digital receivers  126 . The local receiver database  116  is updated and the provisioning information is forwarded to other sibling local receiver databases  116  and any central receiver database  108  in step  308 . 
   A determination is made in step  312  regarding those digital receivers  126  to deprovision because of revocation or a move away from the content broadcaster  104 . Revocation could be performed when the user of a digital receiver  126  is adjudicated as a pirate or if unauthorized modifications to the digital receiver are detected, for example. The central receiver database  108  and sibling local receiver databases  116  can be used to determine which receivers  126  have moved or been revoked. The revoked and moved receivers are removed from the local receiver database in step  316 . Only those entries remaining in the local receiver database  116  receive RMMs. 
   In step  320 , it is determined if the RMM will soon expire. Where the RMM is still valid and not expiring soon, processing loops back to step  304 . This embodiment sends the new RMM out three times before switching over to a new RCM that utilizes a different category key. It can take considerable time to send the RMM uniquely encrypted with a unit key for each digital receiver  126 . The digital receiver may be given two category keys in a RMM such that the following RMM is also available when the preceding RMM expires. In step  324 , the RMM with a switch-over time is broadcast to each digital receiver  126  in the local database  116 . Step  324  could be performed in a loop on a given data channel such that the content broadcaster  104  continually cycles through the entries in the local database  116  to provide RMMs. Some embodiments could have multiple channels for distributing RMMs. Where two-way communication is available between the content broadcaster  104  and the digital receiver  126 , the RMM could be sent a single time if receipt were acknowledged. 
   The switch-over time supercedes any expiration date for the old RMM. It may be necessary to switch-over to a new category key before it expires if the category key has been compromised. For example, a first RMM may expire in one year. Six months into that year, a second RMM could be distributed with a switch-over date of the following month. This will, in-effect, expire the first RMM in the seventh rather than the twelfth month. 
   In some cases, a digital receiver  126  could have missed some RMMs and not be able to decode protected DTV without the current category key. A query could be made either automatically or manually to the content broadcaster  104  to quickly broadcast the RMM for that receiver  126 . With two-way communication the RMM could be singlecasted back to the receiver  126 . 
   In step  328 , RCMs are encrypted with the old category key until the switch-over time or expiration date. Once the old RMM and associated category key expires, the programs sent after that time use the new RMM&#39;s category key to encode their RCMs in step  332 . Since the moved and revoked receivers  126  are not in the local database  116 , they will not receive the new RMM and category key. Any programs sent after step  328  only utilize the new category key, and will be undecipherable to the moved and revoked receivers  126 . 
   Referring to  FIG. 4 , a flow diagram of an embodiment of a process  400  for managing cryptographic functions with the digital receiver  126  is shown. The depicted portion of the process  400  begins in step  404  where the digital receiver  126  provisions in the DMA by sending provisioning information. In this embodiment, the provisioning information includes a unit key, unique serial number and certificate. Some embodiments could use a unit key or unique serial number and forgo authentication with a certificate. 
   A RMM is received in step  408  from a digital data stream. The data stream could be on a special content channel, a control/data channel, or some other data channel. The RMM is decrypted in step  412  using the private unit key resident in the digital receiver  126 . A header on the RMM indicates the unique serial number of the digital receiver  126 . Decryption of the RMM reveals the currently valid category key. Information in the RMM indicates what channels and/or PIDs correspond to the category key. There could be any number of category keys for the various channels and/or PIDs. 
   To tune in a protected channel, the carrier signal is decoded for that channel. The program is identified with a PID in the decoded data stream. An RCM is received from the data stream for that program in step  416 . The RCM is decrypted with the current category key to reveal the content key. In step  424 , the content key is used to decrypt the program, which is displayed in step  428 . 
   Where it is determined the program was not unscrambled properly because of a bad RMM and category key, processing loops back to step  404  for reprovisioning. If the RMM is not invalid after watching the program, processing loops back to step  416  to watch additional programs. If the RMM expires or switches over during viewing of the program, processing loops back to step  408  to receive a new RMM and valid category key. In many cases, the RMM for the next time period is already available such that acquisition is unnecessary. Other embodiments could be constantly watching a RMM channel to receive any RMM addressed to a specific receiver  126 . 
   A number of variations and modifications of the invention can also be used. For example, instead of assigning a unit key to each digital receiver  126  during manufacture, this key could be assigned during the provisioning process. Various embodiments could distribute RMM and RCM in any number of ways such as broadcast, multicast, singlecast, etc. 
   While the principles of the invention have been described above in connection with specific apparatuses and methods, it is to be clearly understood that this description is made only by way of example and not as limitation on the scope of the invention.