Patent Publication Number: US-8996862-B2

Title: Client device and local station with digital rights management and methods for use therewith

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present U.S. Utility Patent Application claims priority pursuant to 35 U.S.C. §120, as a continuation, to the following U.S. Utility Patent Application which is hereby incorporated herein by reference in its entirety and made part of the present U.S. Utility Patent Application for all purposes:
         1. U.S. Utility application Ser. No. 13/027,032, entitled CLIENT DEVICE AND LOCAL STATION WITH DIGITAL RIGHTS MANAGEMENT AND METHODS FOR USE THEREWITH, filed Feb. 14, 2011, which issued as U.S. Pat. No. 8,458,459 on Jun. 4, 2013.       

    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to the digital rights management, and the distribution of protected content such as audio and video programming. 
     DESCRIPTION OF RELATED ART 
     The number of households having multiple television sets is increasing, and many users want the latest and greatest video viewing services. As such, many households have multiple satellite receivers, cable set-top boxes, modems, et cetera. For in-home Internet access, each computer or Internet device can have its own Internet connection. As such, each computer or Internet device includes a modem. 
     As an alternative, an in-home wireless local area network may be used to provide Internet access and to communicate multimedia information to multiple devices within the home. In such an in-home local area network, each computer or Internet device includes a network card to access an IP gateway. The gateway provides the coupling to the Internet. The in-home wireless local area network can also be used to facilitate an in-home computer network that couples a plurality of computers with one or more printers, facsimile machines, as well as to multimedia content from a digital video recorder, set-top box, broadband video system, etc. 
     Certain media content, such as movies, songs, and music albums can be protected by digital rights management techniques that are meant to restrict unlicensed copying of copyrighted materials. For instance, music compact disks (CDs), video cassettes and digital video disks (DVDs) are recorded with copy protection signals that are meant to prevent the media content contained on these media from being copied. 
     Video signals are frequently scrambled during transmission in order to protect the content from unauthorized reception and viewing. An authorized viewer is provided an encryption key that is used to descramble the video content for playback. If a hacker or other unauthorized person gains access to an encryption key, they are also able to descramble the video content for playback. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  presents a pictorial representation of a content distribution system that includes digital rights management in accordance with an embodiment of the present invention. 
         FIG. 2  presents a block diagram representation of client device  10  in accordance with an embodiment of the present invention. 
         FIG. 3  presents a block diagram representation of client device  10  and local station  50  in accordance with an embodiment of the present invention. 
         FIG. 4  presents a block diagram representation of a local instance certificate list in accordance with an embodiment of the present invention. 
         FIG. 5  presents a block diagram representation of client device  10  and local station  50  in accordance with an embodiment of the present invention. 
         FIG. 6  presents a block diagram representation of client device  10  and local station  50  in accordance with an embodiment of the present invention. 
         FIG. 7  presents a flowchart representation of a method in accordance with an embodiment of the present invention. 
         FIG. 8  presents a flowchart representation of a method in accordance with an embodiment of the present invention. 
         FIG. 9  presents a flowchart representation of a method in accordance with an embodiment of the present invention. 
         FIG. 10  presents a flowchart representation of a method in accordance with an embodiment of the present invention. 
         FIG. 11  presents a flowchart representation of a method in accordance with an embodiment of the present invention. 
         FIG. 12  presents a flowchart representation of a method in accordance with an embodiment of the present invention. 
         FIG. 13  presents a flowchart representation of a method in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION INCLUDING THE PRESENTLY PREFERRED EMBODIMENTS 
       FIG. 1  presents a pictorial representation of a content distribution system that includes digital rights management in accordance with an embodiment of the present invention. In particular, a local station  50  is capable of accessing and distributing content from one or more content providers  40  to a plurality of client devices such as a television  60 , smart phone, internet tablet or other personal media players  62  and  64 , handheld video player  66 , and personal computer  68 . While specific client devices are shown, local station  50  is capable of accessing and distributing content from one or more content providers  40  to other client devices that can receive and reproduce media content from media content providers  40 . The local station  50  can be a stand-alone device such as QewStation made available from Morega, Systems, Inc. or a router, set top box, digital video recorder, gateway or other device that includes the functionality attributed to local station  50  as described herein. 
     Local station  50  includes one or more device interfaces, such as a network card, port, data interface, wireless or wired modem or other transceiver or interface device for communicating with the media content providers  40 , with the television  60 , smart phone, internet tablet or other personal media players  62  and  64 , handheld video player  66 , personal computer  68 , and further with certification authority  30 . In particular, certification authority  30  operates in conjunction with local station  50  to implement a digital rights management (DRM) scheme for the media content distributed by local station  50  to the various client devices. 
     In one example of operation, the DRM operates based on a version certificate for each client device that is assigned by the certification authority  30  and stored in the client device. The version certificate includes a private key of a public key cryptography system. During setup and installation of the client device, another certificate, an instance certificate, is applied for and obtained by the client device from the certification authority  30 . The instance certificate includes a public key corresponding the client device&#39;s private key along with a version identifier corresponding to, for example, a version number of the version certificate. 
     When a client device is activated, i.e. when its instance certificate is issued by the certification authority  30 , it is able to register with a local station  50  in order to receive media content. The registration process involves providing its instance certificate to the local station  50  to be included in a local instance certificate list. Once the client device&#39;s instance certificate is listed with a local station  50 , the client device is able to request and receive media content via the local station  50 . For example, when the local station  50  wants to send media content to the client, it uses the public key included in the instance certificate listed for that device to encrypt a content key that is sent to the client device as encrypted data. The client device can decrypt the content key using its private key from its version certificate. When the local station  50  sends media content to the client device, the media content is encrypted with the content key so that only that specified client can read it. A number of client certificates can be added to that process; the cryptographic messaging syntax (CMS) set forth in the request for comments (RFC) 3852 of the Internet Engineering Task Force (IETF) can be used. 
     When a client device is upgraded with a new version certificate, it will be issued a new instance certificate. It can keep the old instance certificate with the old private key to be able to decrypt older content, that for example could be stored on the device. 
     In this configuration, the certificate authority  30  can revoke a client device&#39;s access in more than one way. For revocation of a specific client device, for example, when the device is reported as stolen or is no longer paying its bills, the certification authority  30  can add its instance certificate to a certificate revocation list that is sent to either a particular local station  50  or to all local stations in a network. In another case, where, for example, an entire version has been compromised by hackers, the entire version can revoked by revocation of the corresponding version number at each of the local stations including local station  50 . Simultaneously, the certification authority  30  can stop issuing new instance certificates for that version. 
     The advantages of this DRM scheme includes the following:
         Revocation of an individual installation of a client (e.g. for not paying bills).   Revocation of an entire build/version of clients (e.g. for being hacked)   Binding of content to a group of clients for a particular local station  50     Local station  50  will only talk with registered clients having valid instance certificates   Client devices are still able to access old content after version upgrade   The certification authority can enforce various security and business rules (account in good standing, valid credentials provided, service subscribed to etc.) before issuing the instance certificate.   The ability of registered client devices to copy and share the same content with other registered client devices, without the need to re-encrypt it.       

     The local station  50 , certification authority  30 , and the client devices, such as television  60 , smart phone, internet tablet or other personal media players  62  and  64 , handheld video player  66 , and personal computer  68 , each include one or more features of the present invention described further in conjunction with  FIGS. 2-13  that follow. 
       FIG. 2  presents a block diagram representation of client device  10  in accordance with an embodiment of the present invention. Elements from prior figures are incorporated that are referred to by common reference numerals. In particular, a client device  10  is shown, such as television  60 , smart phone, internet tablet or other personal media players  62  and  64 , handheld video player  66  and/or personal computer  68 . Client device  10  includes a processing module  200 , memory module  202 , cryptography module  210 , interface module  206 , display device  204  and user input interface  212 , that are coupled via bus  218 . While a particular bus architecture is shown, other architectures that include two or more buses and/or direct connectivity between one or more modules of client device  10  are also possible within the scope of the present invention. Further, client device  10  can optionally include additional modules and components, for instance, for performing additional functions and features of the device, depending on its implementation. 
     Client device  10  can be coupled to display video content on its own optional display device  204  such as a liquid crystal display, light emitting diode (LED) backlit display, or other display device, including speakers. In addition or in the alternative, the client device  10  optionally couples to an external display device such as computer monitor, television receiver, external speakers, headphones, et cetera. In an embodiment of the present invention, interface module  206  includes a wired link for coupling to local  50 . The coupling can include a serial or parallel connection such as an Ethernet connection, Universal Serial Bus (USB) connection, an Institute of Electrical and Electronics Engineers (IEEE) 1394 (Firewire) connection, small computer serial interface (SCSI), high definition media interface (HDMI) connection or other wired connection that operates in accordance with either a standard or custom interface protocol. 
     In addition or in the alternative, the interface module  206  can include a wireless link for coupling to the local station  50  either directly or indirectly through one or more devices that operate in accordance with a wireless network protocol such as 802.11a,b,g,n (referred to generically as 802.11x), Bluetooth, Ultra Wideband (UWB), 3G wireless data connection, 4G wireless data connection or other wireless connection that operates in accordance with either a standard or custom interface protocol in order to communicate with one or more of these other devices. 
     In addition, interface module  206  can include a port, such as a card slot or other connection that is coupleable to a removable memory device such as a memory stick, memory card, flash memory device or other memory that transfers data via a digital data file. User input interface  212  includes one or more buttons, a keyboard, a touch pad, a touch screen, thumb wheel and/or other user interface devices that generate signals in response to the action of the user for allowing the user to interact with the device, by making selections, entering data, etc. 
     Processing module  200  can be implemented using a single processing device or a plurality of processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on operational instructions that are stored in a memory, such as memory module  202 . Memory module  202  may be a single memory device or a plurality of memory devices. Such a memory device can include a hard disc drive or other disc drive, read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, cache memory, and/or any device that stores digital information. Note that when the processing module implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory storing the corresponding operational instructions may be embedded within, or external to, the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. 
     Memory module  202  can store a resident video player application, user selections, preferences and other user attribute data, application data corresponding to other applications of the client device  10 , the operating system, other software and firmware, and other data. Additionally, memory module  202  can store a plurality of compressed video files corresponding to stored instances of video content. As discussed above, memory module  202  can include a plurality of different memory devices such as random access memory (RAM), read only memory (ROM), and removable storage devices. In an embodiment of the present invention, memory module  202  includes a flash memory card, memory stick or other flash memory device. 
     Cryptography (crypto) module  210  operates one or more cryptography algorithms such as data encryption standard (DES), Rivest, Shamir, Adelman (RSA), elliptical curve cryptography (ECC) or other algorithm to assist in processing digital signatures or other certificates used in authenticating the client device  10 , and further for decrypting data received from local station  50 . Cryptography module  210  can be implemented via a stand alone processing device or via firmware or software stored in memory module  202  and executed via processing module  200 . 
     Memory module  202  stores a current version certificate that includes a version public key of a public key cryptosystem having an associated version private key. The current version certificate has a corresponding current version identifier, such as a version number or other identifier, that can be used to quickly reference and distinguish the current version certificate from past and future version certificates. The version certificates can be signed by the certification authority for authentication purposes pursuant to a digital signature algorithm such as elliptic curve digital signature algorithm (ECDSA). 
     During setup and installation of the client device  10  or after the device has been upgraded with new software or firmware to include a new version certificate, an instance certificate, is applied for and obtained by the client device from the certification authority  30 . The instance certificate  32  includes the current version identifier of the current version certificate, for example a version number or other identifier. The instance certificate  32  also includes a current instance public key corresponding to a current instance private key. The current instance private key can either be generated locally by cryptography module  210  or received from the certification authority  30 . In addition, the instance certificate is also digitally signed by the certification authority for authentication purposes. In an embodiment of the present invention, the current version certificate can be embedded in an executable program such as cryptography utility, a video player application or other software or firmware in order to make the current version certificate more difficult to access by unauthorized parties. In the alternative, the current version certificate can be stored in a secure key storage module of memory module  202 . It should be noted that both version and instance private keys can also be hidden or obfuscated using either a commercially available source code hardening technique, or a commercially available whitebox cryptography product. 
     In particular, the processing module  200  executes a routine that communicates with certification authority  30  to receive the instance certificate  32 . For example, the interface module  206  can access the certification authority  30  via an internet connection, such as a secure socket layer (SSL) internet connection or other secure connection. The client device  10  shares its current version certificate with the certification authority  30  for purposes of authenticating the client device  10  to the certification authority  30  and further to receive an instance certificate  32  that corresponds to the current version certificate. 
     When a client device  10  is upgraded with a new version certificate, a new instance certificate can be applied for and issued in a similar fashion. Client device  10  can keep the old instance certificate and version certificate with the old private key to be able to decrypt older content. As will be discussed further in conjunction with  FIG. 6 , content received from the local station  50  using the old instance certificate could be stored in memory module  202  for later playback via the client device  10 . 
     The process of obtaining or re-obtaining the instance certificate  32  can follow a number of protocols. In one example, the client device  10  generates an instance private key, as well as a certificate request (e.g. a certificate signing request as set forth in the PKCS#10 specification as defined by RSA labs). The certificate request is sent to the certification authority  30 , which signs it and sends back a signed certificate. In another example, the client device  10  applies for a certificate, and the certification authority generates an instance private key and a certificate for the client. Both the instance private key and the instance certificate are sent back to the client over a secure channel. 
     The instance and/or version certificates can be X.509 certificates, as defined in IETF RFC 2459. The certificates can be used directly in transport layer security (TLS) protocol as defined in IETF RFC 2246, or other secure channels. As discussed, the version certificate can be used to authenticate the client device  10  to the certification authority  30  during the certificate request process; and the instance certificate can be used to authenticate the client device  10  to the local station  50 , or other components of the system (such as a remote server), after the client device has been activated. 
     Further use of the instance certificate by the client device  10 , including several optional functions and features will be discussed in conjunction with  FIGS. 3-13  that follow. 
       FIG. 3  presents a block diagram representation of client device  10  and local station  50  in accordance with an embodiment of the present invention. Elements from prior figures are incorporated that are referred to by common reference numerals. Local station  50  includes a processing module  220 , memory module  222 , cryptography module  230 , interface module  226 , and user input interface  232 , that are coupled via bus  228 . While a particular bus architecture is shown, other architectures that include two or more buses and/or direct connectivity between one or more modules of local station  50  are also possible within the scope of the present invention. Further, local station  50  can optionally include additional modules and components, for instance, for performing additional functions and features of the device, depending on its implementation. 
     In an embodiment of the present invention, interface module  226  includes a wired link for coupling local station  50  to any of the client devices  10 . The coupling can include a serial or parallel connection such as an Ethernet connection, Universal Serial Bus (USB) connection, an Institute of Electrical and Electronics Engineers (IEEE) 1394 (Firewire) connection, small computer serial interface (SCSI), high definition media interface (HDMI) connection or other wired connection that operates in accordance with either a standard or custom interface protocol. In addition or in the alternative, the interface module  226  can include a wireless link for the local station  50  to any of the client devices  10 , either directly or indirectly through one or more devices that operate in accordance with a wireless network protocol such as 802.11a,b,g,n (referred to generically as 802.11x), Bluetooth, Ultra Wideband (UWB), 3G wireless data connection, 4G wireless data connection or other wireless connection that operates in accordance with either a standard or custom interface protocol. The interface module  226  can also include a wired or wireless connection for coupling local station  50  to certification authority  30  and further to one or more media content providers via an internet connection, cable network, telephone network, or other network connection. 
     In addition, interface module  226  can include a port, such as a card slot or other connection that is coupleable to a removable memory device such as a memory stick, memory card, flash memory device or other memory for transferring data via a digital data file. User input interface  232  includes one or more buttons, a keyboard, a touch pad, a touch screen, thumb wheel and/or other user interface devices that generate signals in response to the action of the user of local station  50  for allowing the user to interact with the device, by making selections, entering data, etc. 
     Processing module  220  can be implemented using a single processing device or a plurality of processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on operational instructions that are stored in a memory, such as memory module  222 . Memory module  222  may be a single memory device or a plurality of memory devices. Such a memory device can include a hard disc drive or other disc drive, read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, cache memory, and/or any device that stores digital information. Note that when the processing module implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory storing the corresponding operational instructions may be embedded within, or external to, the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. 
     Memory module  222  can store a local station application, user selections, preferences and other user attribute data, and application data corresponding to other applications of the local station  50 , the operating system, other software and firmware, and other data. Additionally, memory module  222  can store a plurality of compressed video files corresponding to stored instances of video content. As discussed above, memory module  222  can include a plurality of different memory devices such as random access memory (RAM), read only memory (ROM), and removable storage devices. In an embodiment of the present invention, memory module  222  includes a flash memory card, memory stick or other flash memory device. 
     Cryptography (crypto) module  230  operates one or more cryptography algorithms such as data encryption standard (DES), Rivest, Shamir, Adelman (RSA), elliptical curve cryptography (ECC) or other algorithm to assists in processing digital signatures or other certificates used in authenticating the local station  50  and communications from other devices, and further for encrypting data that is sent to any of the client devices  10 . Cryptography module  230  can be implemented via a stand alone processing device or via firmware or software stored in memory module  222  and executed via processing module  220 . 
     When a client device  10  is activated, i.e. when its instance certificate is issued by the certification authority  30 , it is able to register with local station  50  in order to receive media content via that local station. The registration process involves a client device  10  providing its instance certificate  32  to the local station  50  to be included in its local instance certificate list  55 . As discussed in conjunction with  FIG. 2 , the instance certificate  32  was signed by the certification authority  30 . In an embodiment of the present invention, the processing module  220  operates in conjunction with cryptography module  230  to authenticate the instance certificate  32  as originating from the certificate authority  30 , as a precondition for including the instance certificate  32  on the local instance certificate list  55  of memory module  222 . 
       FIG. 4  presents a block diagram representation of a local instance certificate list in accordance with an embodiment of the present invention. Elements from prior figures are incorporated that are referred to by common reference numerals. In particular, the local instance certificate list  55  includes a plurality of instance certificates  32  corresponding to the client devices  10  that have been successfully registered with the local station  50 . As previously discussed, each instance certificate includes both the current instance public key for the client device as well as a current version identifier that identifies the current version of the version certificate of the client device. While the instance certificate is shown as a single field in the local instance certificate list  55 , the current instance public key and current version number could be stored separately or otherwise separately indexed to facilitate faster public key retrieval, and faster deregistration of client devices  10  based on revoked versions. As shown, the local instance certificate list  55  can optionally correlate each instance certificate to a device identifier of the corresponding client device, such as a name, number or other identifier. 
     The local instance certificate list  55  can also optionally correlate each instance certificate to one or more additional certificates that can be securely shared between local station  50  and each particular client device  10 . For example, once a client device&#39;s instance certificate  32  is authenticated, local station  50  can generate one or more additional certificates for that device that are particular to the pairing between the local station  50  and a particular client device  10 . The client device&#39;s public key can be used to encrypt these additional certificates so that they can be sent securely to the particular client device  10 . These additional certificates can be used, for example, to authenticate requests for content and other communications from the client device  10 . 
     As shown, the local instance certificate list  55  can also optionally correlate each instance certificate to a status indicator that indicates, for example whether the instance certificate is active or whether the registration of the client device has been revoked, for example a revocation for a particular client device or group of client devices by the certification authority  30  due to non-payment of bills, due to a wider revocation by the certification authority  30  of a particular version, due to expiration of an instance certificate, or due to other revocation. While the statuses shown in the local instance certificate list  55  include “active” and “revoked” status can further include an optional expiration date, a status, such as “expiring in 3 days”, a particular revocation status, such as “revoked for non-payment”, etc. Further, while the status field is shown as an alphanumeric field, number codes likewise can be used to represent each allowed status condition. 
     Once the client device&#39;s instance certificate  32  is listed with a local station  50 , the client device  10  is able to request and receive media content via the local station  50 . It should be noted that the local station can optionally send all or portions of the local instance certificate list  55  to a remote server (not shown) for tracking purposes via a secure internet connection established between the local station  50  and remote server. Optional additional certificates may or may not be included in versions of the local instance certificate list  55  sent to the remote server. 
       FIG. 5  presents a block diagram representation of client device  10  and local station  50  in accordance with an embodiment of the present invention. Elements from prior figures are incorporated that are referred to by common reference numerals. In this exchange, the client device  10  can issue a request for content  54 . The request for content  54 , generated via processing module  200  in response to user input received via user input interface  212 , can include an indication of the particular content requested, an identification of particular client device  10 , information regarding the display capabilities of the client device  10  and/or the desired format of the content, a particular media content provider  40  and other optional data corresponding to the request. Client device  10  can optionally employ cryptography module  210  to sign the request for content  54  in order to allow local station  50  to verify that the request for content originated from client device  10 . 
     The request for content  54  is encoded as data that is communicated from client device  10  to local station  50  via interface modules  206  and  226 . The data corresponding to the request for content  54  is interpreted by processing module  220  and authenticated. The processing module  220  accesses the local instance certificate list  55  in response to the request. The authentication can include verification of the client device&#39;s signature via cryptography module  230  to determine that the request originated from a valid client device  10 . The authentication can also include determining if the local instance certificate of the requesting client device  10  is active or has been revoked. When the request for content  54  is authenticated, processing module  220  optionally identifies a particular media content provider to fulfill the request, based on the particular content requested, an identification of a particular media content provider  40  included in the request, a determination of the availability of a particular media content provider  40  or based on other factors such as costs, time of retrieval, etc. Processing module  220  communicates with the particular media content provider  40  via interface module  226  to receive the media content  42 . It should be noted that media content  42  may be encrypted by media content provider  40  for transmission to local station  50 , in which case, cryptography module  230  operates to decrypt the media content  42 . 
     If the request for content  54  cannot be authenticated, either because the client device  10  cannot be authenticated, or because the current instance certificate for that client device has been revoked, the request for content  54  is either ignored or in the case where the current instance certificate has been revoked, a return message can be generated by processing module  220  and sent to client device  10  via interface modules  226  and  206  indicating the revoked status and optionally prompting the user to contact the certification authority  30  or other service provider. 
     Processing module  220  optionally operates to transcode the media content  42 . For example, in the instance where the media content  42  includes a digital video signal, the transcoding can include changing the compression format, frame rate, resolution, color depth, aspect ratio, or other parameters of the digital video signal from the format as received into a format suitable for or otherwise requested by the particular client device  10 . 
     The processing module  220  retrieves the public key of the client device  10  from the local instance certificate list  55 . The processing module first generates or retrieves a content key to be used to encrypt the content. The cryptography module  230  generates encrypted data by encrypting the content key via the public key. Processing module  220  formats and sends the encrypted data for transmission to the client device  10  via interface modules  226  and  206 . The processing module  200  commands the cryptography module  210  to decrypt the encrypted data via the private key included in the current version certificate of client device  10 . The decrypted content key can then be stored in memory module  202  for use in decrypting the encrypted content to follow. 
     The cryptography module  230  generates additional encrypted data that includes encrypted content  52 . In particular, cryptography module  230  encrypts or re-encrypts the media content  42 , after optional transcoding, via the content key. Processing module  220  formats and sends the encrypted data  52  for transmission to the client device  10  via interface modules  226  and  206 . The processing module  200  commands the cryptography module  210  to decrypt the encrypted data  52  via the received content key. 
     It should be noted that the processing module  220  can encrypt the content key using one or more other instance public keys corresponding to one or more other client devices  10  associated with a local station  50 . In this mode of operation, the content key and encrypted data  52  can be securely shared between a group of client devices  10  associated with a local station  50 . Each client device  10  is able to decrypt the encrypted data  52  using its own private key to decrypt the content key. In this fashion, media content for a plurality of client devices  10 , associated with a particular user or group of users, can be bound together and accessed by the entire group or any subset thereof, based on the particular subset of the instance public keys used to encrypt the content key. Registered client devices  10  can copy and share the same content with other registered client devices  10 , without the need to re-encrypt it. 
     The encrypted content  52  can include one or more video signals, optionally including associated audio signals that are either real-time signals in digital format or data files that contain video signals in a digital format. In general, such a video signal can be in a digital format such as a Motion Picture Experts Group (MPEG) format (such as MPEG1, MPEG2 or MPEG4), Quicktime format, Real Media format, H.264 format, Windows Media Video (WMV) or Audio Video Interleave (AVI), or another digital video format, either standard or proprietary. For instance, encrypted content  52  can include content from a broadcast video signal, such as a high definition television signal, enhanced high definition television signal or other digital broadcast video signal that has been transmitted over a wireless medium, either directly or through one or more satellites or other relay stations or through a cable network, optical network, IP television network, or other transmission network. Further, encrypted content  52  include a digital audio/video file, transferred from a storage medium such as a server memory, magnetic tape, magnetic disc or optical disc, or can included a streaming audio or video signal that is transmitted over a public or private network such as a wireless or wired data network, local area network, wide area network, metropolitan area network or the Internet. 
     Client device  10  can be coupled to display video content from encrypted content  52  on its own optional display device  204  display device such as a liquid crystal display, light emitting diode (LED) backlit display, or other display device, including speakers. In addition or in the alternative, the client device  10  optionally couples to an external display device such as computer monitor, television receiver, external speakers, headphones, et cetera. In an embodiment of the present invention, interface module  206  includes a wired link for coupling to media content provider  40  to transfer the encrypted content  52  either directly or through one or more intermediate devices. The coupling can include a serial or parallel connection such as an Ethernet connection, Universal Serial Bus (USB) connection, an Institute of Electrical and Electronics Engineers (IEEE) 1394 (Firewire) connection, small computer serial interface (SCSI) connection or other wired connection that operates in accordance with either a standard or custom interface protocol. 
     While described above, in conjunction with a specific request for content  54 , local station  50  may automatically send content to a particular client device  10 , under certain circumstances such as a scheduled broadcast, push transaction, repeating request or other scenario. Further, while a two stage approach is described above whereby local station uses a client device&#39;s public key to encrypt a content key that is used by local station  50  in encrypting the encrypted content  52 . In a more direct approach, the encrypted content  52  can be directly encrypted via the public key of the particular client device  10 , provided that the encryption algorithm employed, the computational resources of cryptography module  210  and the timing associated with delivery of the media content  42  allow direct decryption. Such a direct approach can be employed in non-streaming applications, or circumstances where cryptography module  210  can decrypt the encrypted signal  52  using the cryptography system associated directly with the version certificate and instance certificate at a sufficient speed to facilitate real-time processing. 
       FIG. 6  presents a block diagram representation of client device  10  and local station  50  in accordance with an embodiment of the present invention. Elements from prior figures are incorporated that are referred to by common reference numerals. As previously discussed, the certificate authority  30  can revoke a client device&#39;s access to content in more than one way. For revocation of a specific client device, for example, when a client device is reported as stolen or is no longer paying its bills, the certification authority  30  can add its instance certificate to a certificate revocation list that is sent to either a particular local station  50  or to all local stations in a network as revocation data  34 . For example, the certificate revocation list can be implemented in accordance with the X.509 standard, as per request for comments (RFC) 5280 of the Internet Engineering Task Force. 
     In another case, where, for example, an entire version has been compromised by hackers, the entire version can revoked by sending revocation data  34  to all local stations including local stations  50  that indicates revocation of all version certificates having that corresponding version identifier. Simultaneously, the certification authority  30  can stop issuing new instance certificates to client devices  10  having version certificates of that version. In either case, the local instance certificate list  55  is updated based on the revocation data  34  to indicate a revoked status of one or more devices, based on the particular instance certificates that are revoked or the particular instance certificates that indicate a corresponding version identifier that has been revoked. 
     As discussed in conjunction with  FIG. 5 , when a request for content  54  is received it is authenticated. Processing module  220  accesses the local instance certification list  55  to determine if the local instance certificate of the requesting client device  10  is active or has been revoked. If the request for content  54  cannot be authenticated, either because the current instance certificate or the current version certification for that client device has been revoked, the request is either ignored or a return message can be generated by processing module  220  and sent to client device  10  via interface modules  226  and  206  indicated the revoked status and optionally prompting the user to contact the certification authority  30  or other service provider. 
     When a client device  10  is upgraded with a new version certificate, a new instance certificate can be applied for and issued in a similar fashion as discussed in conjunction with  FIG. 2 . Client device  10  can keep the old instance certificate and version certificate with the old private key to be able to decrypt older content. In the event that media content  42  has been requested and received via a previous instance certificate and stored in memory module  202 , client device  10  is still able to decrypt and play that content. In particular, memory module  202  stores the current instance certificate along with one or more past instance certificates, each past instance certificate including a past instance public key corresponding to an earlier version certificate having an earlier version identifier than the current version identifier. The processing module  220  identifies when encrypted data received via communications from the local station  50  corresponds to one of the past instance certificate that is encrypted via a past instance public key. The cryptography module  210  decrypts this encrypted data based on the past instance private key. 
       FIG. 7  presents a flowchart representation of a method in accordance with an embodiment of the present invention. In particular a method is presented for use in conjunction with one or more functions and features described in conjunction with  FIGS. 1-6 , such as via a client device  10 . In step  400  a current version certificate is stored that includes a current version public key of a public key cryptosystem, the current version certificate having a corresponding current version identifier. In step  402 , a current instance certificate is received from a certificate authority, wherein the current instance certificate includes the current version identifier of the current version certificate and a current instance public key corresponding to the client&#39;s current instance private key. In step  404 , the current instance certificate is sent to a local station, during a registration with the local station. In step  406 , a request for video content is generated and the request is sent to the local station. In step  408 , first encrypted data is received from the local station, wherein the first encrypted data includes a content key that is encrypted via the current instance public key. In step  410 , second encrypted data is received from the local station, wherein the second encrypted data includes the video content that is encrypted via the content key. 
     In an embodiment of the present invention, the current instance certificate and the current version certificate are signed by the certification authority. 
       FIG. 8  presents a flowchart representation of a method in accordance with an embodiment of the present invention. In particular a method is presented for use in conjunction with one or more functions and features described in conjunction with  FIGS. 1-7 . In step  420 , at least one past instance certificate is stored that includes a past instance public key corresponding to a past instance private key. 
       FIG. 9  presents a flowchart representation of a method in accordance with an embodiment of the present invention. In particular a method is presented for use in conjunction with one or more functions and features described in conjunction with  FIGS. 1-8 . In step  430 , the method identifies when third encrypted data received from the local station corresponds to the at least one past instance certificate that is encrypted via the past instance public key. In step  432 , the third encrypted data is decrypted based on the past instance private key, when the third encrypted data corresponds to the at least one past instance certificate that is encrypted via the past instance public key. 
       FIG. 10  presents a flowchart representation of a method in accordance with an embodiment of the present invention. In particular a method is presented for use in conjunction with one or more functions and features described in conjunction with  FIGS. 1-9 . In step  440 , the client device is authenticated to the certification authority, prior to receiving the current instance certificate, by sending the current version certificate to the certification authority. 
       FIG. 11  presents a flowchart representation of a method in accordance with an embodiment of the present invention. In particular a method is presented for use in conjunction with one or more functions and features described in conjunction with FIGS.  1 - 10 . In step  500 , a plurality of current instance certificates are received from a plurality of client devices, during registrations with the plurality of client devices. In step  502 , the plurality of current instance certificates corresponding to the plurality of client devices are stored, wherein each of the plurality of current instance certificates includes a current version identifier and a current instance public key associated with the current instance private key of a corresponding one of the plurality of client devices. In step  504 , a request is received for video content from one of the plurality of client devices. In decision block  506 , the method accessing one of the plurality of current instance certificates corresponding to the one of the plurality of client devices and determines if the request is authenticated, based the one of the plurality of current instance certificates. When the request is authenticated, the method proceeds to step  508 , to retrieve the requested video content from at least one media content provider; to step  510  to generate first encrypted data and sending the first encrypted data to the one of the plurality of client devices, wherein the first encrypted data includes a content key that is encrypted via the current instance public key; and to step  512  to generate second encrypted data and sending the second encrypted data to the one of the plurality of client devices, wherein the second encrypted data includes the video content that is encrypted via the content key. 
     In an embodiment of the present invention, the current instance certificate is signed by a certification authority. 
     It should also be noted that, in step  510 , the content key can also be encrypted by one or more other public keys corresponding to one or more other client devices associated with a local station. 
       FIG. 12  presents a flowchart representation of a method in accordance with an embodiment of the present invention. In particular a method is presented for use in conjunction with one or more functions and features described in conjunction with  FIGS. 1-11 . In step  520 , revocation data is received from a certification authority, the revocation data indicating the revocation of at least one of the plurality of client devices. In particular, authenticating a request for content can include determining when the one of the plurality of current instance certificates has not been revoked. 
     In an embodiment of the present invention, the revocation data includes a certificate revocation list implemented in accordance with the X.509 standard, as per request for comments (RFC) 5280 of the Internet Engineering Task Force. 
       FIG. 13  presents a flowchart representation of a method in accordance with an embodiment of the present invention. In particular a method is presented for use in conjunction with one or more functions and features described in conjunction with  FIGS. 1-12 . In step  530 , revocation data is received from a certification authority, the revocation data indicating the revocation of at least one version identifier. In particular, authenticating a request for content can include determining when the current version identifier included in the one of the plurality of current instance certificates, has not been revoked. 
     In preferred embodiments, optional circuit components can be implemented using 0.35 micron or smaller CMOS technology. Provided however that other circuit technologies, both integrated or non-integrated, may be used within the broad scope of the present invention. 
     As one of ordinary skill in the art will appreciate, the term “substantially” or “approximately”, as may be used herein, provides an industry-accepted tolerance to its corresponding term and/or relativity between items. Such an industry-accepted tolerance ranges from less than one percent to twenty percent and corresponds to, but is not limited to, component values, integrated circuit process variations, temperature variations, rise and fall times, and/or thermal noise. Such relativity between items ranges from a difference of a few percent to magnitude differences. As one of ordinary skill in the art will further appreciate, the term “coupled”, as may be used herein, includes direct coupling and indirect coupling via another component, element, circuit, or module where, for indirect coupling, the intervening component, element, circuit, or module does not modify the information of a signal but may adjust its current level, voltage level, and/or power level. As one of ordinary skill in the art will also appreciate, inferred coupling (i.e., where one element is coupled to another element by inference) includes direct and indirect coupling between two elements in the same manner as “coupled”. As one of ordinary skill in the art will further appreciate, the term “compares favorably”, as may be used herein, indicates that a comparison between two or more elements, items, signals, etc., provides a desired relationship. For example, when the desired relationship is that signal 1 has a greater magnitude than signal 2, a favorable comparison may be achieved when the magnitude of signal  1  is greater than that of signal 2 or when the magnitude of signal 2 is less than that of signal 1. 
     As the term module is used in the description of the various embodiments of the present invention, a module includes a functional block that is implemented in hardware, software, and/or firmware that performs one or module functions such as the processing of an input signal to produce an output signal. As used herein, a module may contain submodules that themselves are modules. 
     Thus, there has been described herein an apparatus and method, as well as several embodiments including a preferred embodiment, for implementing a media distribution system with digital rights management. Various embodiments of the present invention herein-described have features that distinguish the present invention from the prior art. 
     It will be apparent to those skilled in the art that the disclosed invention may be modified in numerous ways and may assume many embodiments other than the preferred forms specifically set out and described above. Accordingly, it is intended by the appended claims to cover all modifications of the invention which fall within the true spirit and scope of the invention.