Patent Publication Number: US-2002012432-A1

Title: Secure video card in computing device having digital rights management (DRM) system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
     [0001] This application is related to U.S. patent application Ser. No. 09/290,363, filed Apr. 12, 1999 and entitled “ENFORCEMENT ARCHITECTURE AND METHOD FOR DIGITAL RIGHTS MANAGEMENT”, and U.S. Provisional Application No. 60/126,614, filed Mar. 27, 1999 and entitled “ENFORCEMENT ARCHITECTURE AND METHOD FOR DIGITAL RIGHTS MANAGEMENT”, each of which is hereby incorporated by reference in its entirety. 
    
    
     
       TECHNICAL FIELD  
       [0002] The present invention relates to an architecture for enforcing rights in digital content. More specifically, the present invention relates to such an enforcement architecture that allows access to encrypted digital content only in accordance with parameters specified by license rights acquired by a user of the digital content. Even more specifically, the present invention relates to ensuring that a device that receives un-encrypted digital content, such as a video card in a computing device, can be trusted.  
       BACKGROUND OF THE INVENTION  
       [0003] Digital rights management and enforcement is highly desirable in connection with digital content such as digital audio, digital video, digital text, digital data, digital multimedia, etc., where such digital content is to be distributed to users. Typical modes of distribution include tangible devices such as a magnetic (floppy) disk, a magnetic tape, an optical (compact) disk (CD), etc., and intangible media such as an electronic bulletin board, an electronic network, the Internet, etc. Upon being received by the user, such user renders or ‘plays’ the digital content with the aid of an appropriate rendering device such as a media player on a personal computer or the like.  
       [0004] Typically, a content owner or rights-owner, such as an author, a publisher, a broadcaster, etc. (hereinafter “content owner”), wishes to distribute such digital content to a user or recipient in exchange for a license fee or some other consideration. Such content owner, given the choice, would likely wish to restrict what the user can do with such distributed digital content. For example, the content owner would like to restrict the user from copying and re-distributing such content to a second user, at least in a manner that denies the content owner a license fee from such second user.  
       [0005] In addition, the content owner may wish to provide the user with the flexibility to purchase different types of use licenses at different license fees, while at the same time holding the user to the terms of whatever type of license is in fact purchased. For example, the content owner may wish to allow distributed digital content to be played only a limited number of times, only for a certain total time, only on a certain type of machine, only on a certain type of media player, only by a certain type of user, etc.  
       [0006] However, after distribution has occurred, such content owner has very little if any control over the digital content. This is especially problematic in view of the fact that practically every new or recent personal computer includes the software and hardware necessary to make an exact digital copy of such digital content, and to download such exact digital copy to a write-able magnetic or optical disk, or to send such exact digital copy over a network such as the Internet to any destination.  
       [0007] Of course, as part of the legitimate transaction where the license fee was obtained, the content owner may require the user of the digital content to promise not to re-distribute such digital content. However, such a promise is easily made and easily broken. A content owner may attempt to prevent such re-distribution through any of several known security devices, usually involving encryption and decryption. However, there is likely very little that prevents a mildly determined user from decrypting encrypted digital content, saving such digital content in an un-encrypted form, and then re-distributing same.  
       [0008] A need exists, then, for providing an enforcement architecture and method that allows the controlled rendering or playing of arbitrary forms of digital content, where such control is flexible and definable by the content owner of such digital content. A need also exists for providing a controlled rendering environment on a computing device such as a personal computer, where the rendering environment includes at least a portion of such enforcement architecture. Such controlled rendering environment allows that the digital content will only be rendered as specified by the content owner, even though the digital content is to be rendered on a computing device which is not under the control of the content owner.  
       [0009] Further, a need exists for a trusted component running on the computing device, where the trusted component enforces the rights of the content owner on such computing device in connection with a piece of digital content, even against attempts by the user of such computing device to access such digital content in ways not permitted by the content owner. Additionally, a need exists for a secure video card on the computing device to prevent a content thief from stealing content residing on/destined for the video card.  
       SUMMARY OF THE INVENTION  
       [0010] The aforementioned needs are satisfied at least in part by an enforcement architecture and method for digital rights management, where the architecture and method enforce rights in protected (secure) digital content available on a medium such as the Internet, an optical disk, etc. For purposes of making content available, the architecture includes a content server from which the digital content is accessible over the Internet or the like in an encrypted form. The content server may also supply the encrypted digital content for recording on an optical disk or the like, wherein the encrypted digital content may be distributed on the optical disk itself. At the content server, the digital content is encrypted using an encryption key, and public/private key techniques are employed to bind the digital content with a digital license at the user&#39;s computing device or client machine.  
       [0011] When a user attempts to render the digital content on a computing device, the rendering application invokes a Digital Rights Management (DRM) system on such user&#39;s computing device. If the user is attempting to render the digital content for the first time, the DRM system either directs the user to a license server to obtain a license to render such digital content in the manner sought, or transparently obtains such license from such license server without any action necessary on the part of the user. The license includes:  
       [0012] a decryption key (KD) that decrypts the encrypted digital content;  
       [0013] a description of the rights (play, copy, etc.) conferred by the license and related conditions (begin date, expiration date, number of plays, etc.), where such description is in a digitally readable form; and  
       [0014] a digital signature that ensures the integrity of the license.  
       [0015] The user should not be able to decrypt and render the encrypted digital content without obtaining such a license from the license server. The obtained license is stored in a license store in the user&#39;s computing device.  
       [0016] Importantly, the license server only issues a license to a DRM system that is ‘trusted’ (i.e., that can authenticate itself). To implement ‘trust’, the DRM system is equipped with a ‘black box’ that performs decryption and encryption functions for such DRM system. The black box includes a public/private key pair, a version number and a unique signature, all as provided by an approved certifying authority. The public key is made available to the license server for purposes of encrypting portions of the issued license, thereby binding such license to such black box. The private key is available to the black box only, and not to the user or anyone else, for purposes of decrypting information encrypted with the corresponding public key. The DRM system is initially provided with a black box with a public/private key pair, and the user is prompted to download from a black box server an updated secure black box when the user first requests a license. The black box server provides the updated black box, along with a unique public/private key pair. Such updated black box is written in unique executable code that will run only on the user&#39;s computing device, and is re-updated on a regular basis.  
       [0017] When a user requests a license, the client machine sends the black box public key, version number, and signature to the license server, and such license server issues a license only if the version number is current and the signature is valid. A license request also includes an identification of the digital content for which a license is requested and a key ID that identifies the decryption key associated with the requested digital content. The license server uses the black box public key to encrypt the decryption key, and the decryption key to encrypt the license terms, then downloads the encrypted decryption key and encrypted license terms to the user&#39;s computing device along with a license signature.  
       [0018] Once the downloaded license has been stored in the DRM system license store, the user can render the digital content according to the rights conferred by the license and specified in the license terms. When a request is made to render the digital content, the black box is caused to decrypt the decryption key and license terms, and a DRM system license evaluator evaluates such license terms. The black box decrypts the encrypted digital content only if the license evaluation results in a decision that the requester is allowed to play such content. The decrypted content is provided to the rendering application for rendering.  
       [0019] In the present invention, a computing device includes a digital rights management (DRM) system thereon for allowing rendering of rights-protected digital content on the computing device only in accordance with rights specified in a corresponding digital license. The content includes video content to be displayed on a monitor coupled to the computing device. The computing device also includes a video section therein for receiving the content and for producing a video signal to be sent to the monitor based on the received content. The video section includes video memory for storing the received content, and the video memory is configured to be write-only except with regard to the video section. The video section further includes an authentication device for authenticating to the DRM system that the video memory is configured to be write-only except with regard to the video section.  
       [0020] A secure computing environment is thus created which can render video data to an output device in such a way that no other software component on the computing device can read the data so written. The video section supports secure output either by presenting a video buffer that is write-only with respect to applications or operating system components that access such video section, or the video section can establish an encrypted connection with a local process or remote entity to effectively hide transmitted and rendered data.  
       [0021] The producer of the data must be assured that data sent to the video section is truly sent to the video section and not to malicious software masquerading as a video section Such assurance may be achieved by way of cryptographic authentication. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0022] The foregoing summary, as well as the following detailed description of the embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. As should be understood, however, the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:  
     [0023]FIG. 1 is a block diagram showing an enforcement architecture in accordance with one embodiment of the present invention;  
     [0024]FIG. 2 is a block diagram of the authoring tool of the architecture of FIG. 1 in accordance with one embodiment of the present invention;  
     [0025]FIG. 3 is a block diagram of a digital content package having digital content for use in connection with the architecture of FIG. 1 in accordance with one embodiment of the present invention;  
     [0026]FIG. 4 is a block diagram of the user&#39;s computing device of FIG. 1 in accordance with one embodiment of the present invention;  
     [0027]FIGS. 5A and 5B are flow diagrams showing the steps performed in connection with the Digital Rights Management (DRM) system of the computing device of FIG. 4 to render content in accordance with one embodiment of the present invention;  
     [0028]FIG. 6 is a flow diagram showing the steps performed in connection with the DRM system of FIG. 4 to determine whether any valid, enabling licenses are present in accordance with one embodiment of the present invention;  
     [0029]FIG. 7 is a flow diagram showing the steps performed in connection with the DRM system of FIG. 4 to obtain a license in accordance with one embodiment of the present invention;  
     [0030]FIG. 8 is a block diagram of a digital license for use in connection with the architecture of FIG. 1 in accordance with one embodiment of the present invention;  
     [0031]FIG. 9 is a flow diagram showing the steps performed in connection with the DRM system of FIG. 4 to obtain a new black box in accordance with one embodiment of the present invention;  
     [0032]FIG. 10 is a flow diagram showing the key transaction steps performed in connection with the DRM system of FIG. 4 to validate a license and a piece of digital content and render the content in accordance with one embodiment of the present invention;  
     [0033]FIG. 11 is a block diagram showing the license evaluator of FIG. 4 along with a Digital Rights License (DRL) of a license and a language engine for interpreting the DRL in accordance with one embodiment of the present invention;  
     [0034]FIG. 12 is a block diagram representing a general purpose computer system in which aspects of the present invention and/or portions thereof may be incorporated; and  
     [0035]FIG. 13 is a block diagram showing the DRM system and rendering application of FIG. 4 and a video card on the computing device of FIG. 1 in accordance with one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0036] Referring to the drawings in details, wherein like numerals are used to indicate like elements throughout, there is shown in FIG. 1 an enforcement architecture  10  in accordance with one embodiment of the present invention. Overall, the enforcement architecture  10  allows an owner of digital content  12  to specify license rules that must be satisfied before such digital content  12  is allowed to be rendered on a user&#39;s computing device  14 . Such license rules are embodied within a digital license  16  that the user/user&#39;s computing device  14  (hereinafter, such terms are interchangeable unless circumstances require otherwise) must obtain from the content owner or an agent thereof. The digital content  12  is distributed in an encrypted form, and may be distributed freely and widely. Preferably, the decrypting key (KD) for decrypting the digital content  12  is included with the license  16 .  
     [0037] Computer Environment  
     [0038]FIG. 12 and the following discussion are intended to provide a brief general description of a suitable computing environment in which the present invention and/or portions thereof may be implemented. Although not required, the invention is described in the general context of computer-executable instructions, such as program modules, being executed by a computer, such as a client workstation or a server. Generally, program modules include routines, programs, objects, components, data structures and the like that perform particular tasks or implement particular abstract data types. Moreover, it should be appreciated that the invention and/or portions thereof may be practiced with other computer system configurations, including hand-held devices, multi-processor systems, microprocessor-based or programmable consumer electronics, network PCs, minicomputers, mainframe computers and the like. The invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote memory storage devices.  
     [0039] As shown in FIG. 12, an exemplary general purpose computing system includes a conventional personal computer  120  or the like, including a processing unit  121 , a system memory  122 , and a system bus  123  that couples various system components including the system memory to the processing unit  121 . The system bus  123  may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. The system memory includes read-only memory (ROM)  124  and random access memory (RAM)  125 . A basic input/output system  126  (BIOS), containing the basic routines that help to transfer information between elements within the personal computer  120 , such as during start-up, is stored in ROM  124 .  
     [0040] The personal computer  120  may further include a hard disk drive  127  for reading from and writing to a hard disk (not shown), a magnetic disk drive  128  for reading from or writing to a removable magnetic disk  129 , and an optical disk drive  130  for reading from or writing to a removable optical disk  131  such as a CD-ROM or other optical media. The hard disk drive  127 , magnetic disk drive  128 , and optical disk drive  130  are connected to the system bus  123  by a hard disk drive interface  132 , a magnetic disk drive interface  133 , and an optical drive interface  134 , respectively. The drives and their associated computer-readable media provide non-volatile storage of computer readable instructions, data structures, program modules and other data for the personal computer  20 .  
     [0041] Although the exemplary environment described herein employs a hard disk, a removable magnetic disk  129 , and a removable optical disk  131 , it should be appreciated that other types of computer readable media which can store data that is accessible by a computer may also be used in the exemplary operating environment. Such other types of media include a magnetic cassette, a flash memory card, a digital video disk, a Bernoulli cartridge, a random access memory (RAM), a read-only memory (ROM), and the like.  
     [0042] A number of program modules may be stored on the hard disk, magnetic disk  129 , optical disk  131 , ROM  124  or RAM  125 , including an operating system  135 , one or more application programs  136 , other program modules  137  and program data  138 . A user may enter commands and information into the personal computer  120  through input devices such as a keyboard  140  and pointing device  142 . Other input devices (not shown) may include a microphone, joystick, game pad, satellite disk, scanner, or the like. These and other input devices are often connected to the processing unit  121  through a serial port interface  146  that is coupled to the system bus, but may be connected by other interfaces, such as a parallel port, game port, or universal serial bus (USB). A monitor  147  or other type of display device is also connected to the system bus  123  via an interface, such as a video adapter  148 . In addition to the monitor  147 , a personal computer typically includes other peripheral output devices (not shown), such as speakers and printers. The exemplary system of FIG. 12 also includes a host adapter  155 , a Small Computer System Interface (SCSI) bus  156 , and an external storage device  162  connected to the SCSI bus  156 .  
     [0043] The personal computer  120  may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer  149 . The remote computer  149  may be another personal computer, a server, a router, a network PC, a peer device or other common network node, and typically includes many or all of the elements described above relative to the personal computer  120 , although only a memory storage device  150  has been illustrated in FIG. 12. The logical connections depicted in FIG. 12 include a local area network (LAN)  151  and a wide area network (WAN)  152 . Such networking environments are commonplace in offices, enterprise-wide computer networks, intranets, and the Internet.  
     [0044] When used in a LAN networking environment, the personal computer  120  is connected to the LAN  151  through a network interface or adapter  153 . When used in a WAN networking environment, the personal computer  120  typically includes a modem  154  or other means for establishing communications over the wide area network  152 , such as the Internet. The modem  154 , which may be internal or external, is connected to the system bus  123  via the serial port interface  146 . In a networked environment, program modules depicted relative to the personal computer  120 , or portions thereof, may be stored in the remote memory storage device. It will be appreciated that the network connections shown are exemplary and other means of establishing a communications link between the computers may be used.  
     [0045] Architecture  
     [0046] Referring again to FIG. 1, in one embodiment of the present invention, the architecture  10  includes an authoring tool  18 , a content-key database  20 , a content server  22 , a license server  24 , and a black box server  26 , as well as the aforementioned user&#39;s computing device  14 .  
     [0047] Architecture—Authoring Tool  18   
     [0048] The authoring tool  18  is employed by a content owner to package a piece of digital content  12  into a form that is amenable for use in connection with the architecture  10  of the present invention. In particular, the content owner provides the authoring tool  18  with the digital content  12 , instructions and/or rules that are to accompany the digital content  12 , and instructions and/or rules as to how the digital content  12  is to be packaged. The authoring tool  18  then produces a digital content package  12   p  having the digital content  12  encrypted according to an encryption/decryption key, and the instructions and/or rules that accompany the digital content  12 .  
     [0049] In one embodiment of the present invention, the authoring tool  18  is instructed to serially produce several different digital content  12  packages  12   p,  each having the same digital content  12  encrypted according to a different encryption/decryption key. As should be understood, having several different packages  12   p  with the same digital content  12  may be useful for tracking the distribution of such packages  12   p /content  12  (hereinafter simply “digital content  12 ”, unless circumstances require otherwise). Such distribution tracking is not ordinarily necessary, but may be used by an investigative authority in cases where the digital content  12  has been illegally sold or broadcast.  
     [0050] In one embodiment of the present invention, the encryption/decryption key that encrypts the digital content  12  is a symmetric key, in that the encryption key is also the decryption key (KD). As will be discussed below in more detail, such decryption key (KD) is delivered to a user&#39;s computing device  14  in a hidden form as part of a license  16  for such digital content  12 . Preferably, each piece of digital content  12  is provided with a content ID (or each package  12   p  is provided with a package ID), each decryption key (KD) has a key ID, and the authoring tool  18  causes the decryption key (KD), key ID, and content ID (or package ID) for each piece of digital content  12  (or each package  12   p ) to be stored in the content-key database  20 . In addition, license data regarding the types of licenses  16  to be issued for the digital content  12  and the terms and conditions for each type of license  16  may be stored in the content-key database  20 , or else in another database (not shown). Preferably, the license data can be modified by the content owner at a later time as circumstances and market conditions may require.  
     [0051] In use, the authoring tool  18  is supplied with information including, among other things:  
     [0052] the digital content  12  to be packaged;  
     [0053] the type and parameters of watermarking and/or fingerprinting to be employed, if any;  
     [0054] the type and parameters of data compression to be employed, if any;  
     [0055] the type and parameters of encryption to be employed;  
     [0056] the type and parameters of serialization to be employed, if any; and  
     [0057] the instructions and/or rules that are to accompany the digital content  12 .  
     [0058] As is known, a watermark is a hidden, computer-readable signal that is added to the digital content  12  as an identifier. A fingerprint is a watermark that is different for each instance. As should be understood, an instance is a version of the digital content  12  that is unique. Multiple copies of any instance may be made, and any copy is of a particular instance. When a specific instance of digital content  12  is illegally sold or broadcast, an investigative authority can perhaps identify suspects according to the watermark/fingerprint added to such digital content  12 .  
     [0059] Data compression may be performed according to any appropriate compression algorithm without departing from the spirit and scope of the present invention. For example, the .mp3 or .wav compression algorithm may be employed. Of course, the digital content  12  may already be in a compressed state, in which case no additional compression is necessary.  
     [0060] The instructions and/or rules that are to accompany the digital content  12  may include practically any appropriate instructions, rules, or other information without departing from the spirit and scope of the present invention. As will be discussed below, such accompanying instructions/rules/information are primarily employed by the user and the user&#39;s computing device  14  to obtain a license  16  to render the digital content  12 . Accordingly, such accompanying instructions/rules/information may include an appropriately formatted license acquisition script or the like, as will be described in more detail below. In addition, or in the alternative, such accompanying instructions/rules/information may include ‘preview’ information designed to provide a user with a preview of the digital content  12 .  
     [0061] With the supplied information, the authoring tool  18  then produces one or more packages  12   p  corresponding to the digital content  12 . Each package  12   p  may then be stored on the content server  22  for distribution to the world.  
     [0062] In one embodiment of the present invention, and referring now to FIG. 2, the authoring tool  18  is a dynamic authoring tool  18  that receives input parameters which can be specified and operated on. Accordingly, such authoring tool  18  can rapidly produce multiple variations of package  12   p  for multiple pieces of digital content  12 . Preferably, the input parameters are embodied in the form of a dictionary  28 , as shown, where the dictionary  28  includes such parameters as:  
     [0063] the name of the input file  29   a  having the digital content  12 ;  
     [0064] the type of encoding that is to take place  
     [0065] the encryption/decryption key (KD) to be employed,  
     [0066] the accompanying instructions/rules/information (‘header information’) to be packaged with the digital content  12  in the package  12   p.    
     [0067] the type of muxing that is to occur; and  
     [0068] the name of the output file  29   b  to which the package  12   p  based on the digital content  12  is to be written.  
     [0069] As should be understood, such dictionary  28  is easily and quickly modifiable by an operator of the authoring tool  18  (human or machine), and therefore the type of authoring performed by the authoring tool  18  is likewise easily and quickly modifiable in a dynamic manner. In one embodiment of the present invention, the authoring tool  18  includes an operator interface (not shown) displayable on a computer screen to a human operator. Accordingly, such operator may modify the dictionary  28  by way of the interface, and further may be appropriately aided and/or restricted in modifying the dictionary  28  by way of the interface.  
     [0070] In the authoring tool  18 , and as seen in FIG. 2, a source filter  18   a  receives the name of the input file  29   a  having the digital content  12  from the dictionary  28 , and retrieves such digital content  12  from such input file and places the digital content  12  into a memory  29   c  such as a RAM or the like. An encoding filter  18   b  then performs encoding on the digital content  12  in the memory  29   c  to transfer the file from the input format to the output format according to the type of encoding specified in the dictionary  28  (i.e., .wav to .asp, .mp3 to asp, etc.), and places the encoded digital content  12  in the memory  29   c.  As shown, the digital content  12  to be packaged (music, e.g.) is received in a compressed format such as the .wav or .mp3 format, and is transformed into a format such as the .asp (active streaming protocol) format. Of course, other input and output formats may be employed without departing from the spirit and scope of the present invention.  
     [0071] Thereafter, an encryption filter  18   c  encrypts the encoded digital content  12  in the memory  29   c  according to the encryption/decryption key (KD) specified in the dictionary  28 , and places the encrypted digital content  12  in the memory  29   c.  A header filter  18   d  then adds the header information specified in the dictionary  28  to the encrypted digital content  12  in the memory  29   c.    
     [0072] As should be understood, depending on the situation, the package  12   p  may include multiple streams of temporally aligned digital content  12  (one stream being shown in FIG. 2), where such multiple streams are multiplexed (i.e., ‘muxed’). Accordingly, a mux filter  18   e  performs muxing on the header information and encrypted digital content  12  in the memory  29   c  according to the type of muxing specified in the dictionary  28 , and places the result in the memory  29   c.  A file writer filter  18   f  then retrieves the result from the memory  29   c  and writes such result to the output file  29   b  specified in the dictionary  28  as the package  12   p.    
     [0073] It should be noted that in certain circumstances, the type of encoding to be performed will not normally change. Since the type of muxing typically is based on the type of encoding, it is likewise the case that the type of muxing will not normally change, either. If this is in fact the case, the dictionary  28  need not include parameters on the type of encoding and/or the type of muxing. Instead, it is only necessary that the type of encoding be ‘hardwired’ into the encoding filter and/or that the type of muxing be ‘hardwired’ into the mux filter. Of course, as circumstance require, the authoring tool  18  may not include all of the aforementioned filters, or may include other filters, and any included filter may be hardwired or may perform its function according to parameters specified in the dictionary  28 , all without departing from the spirit and scope of the present invention.  
     [0074] Preferably, the authoring tool  18  is implemented on an appropriate computer, processor, or other computing machine by way of appropriate software. The structure and operation of such machine and such software should be apparent based on the disclosure herein and therefore do not require any detailed discussion in the present disclosure.  
     [0075] Architecture—Content Server  22   
     [0076] Referring again to FIG. 1, in one embodiment of the present invention, the content server  22  distributes or otherwise makes available for retrieval the packages  12   p  produced by the authoring tool  18 . Such packages  12   p  may be distributed as requested by the content server  22  by way of any appropriate distribution channel without departing from the spirit and scope of the present invention. For example, such distribution channel may be the Internet or another network, an electronic bulletin board, electronic mail, or the like. In addition, the content server  22  may be employed to copy the packages  12   p  onto magnetic or optical disks or other storage devices, and such storage devices may then be distributed.  
     [0077] It will be appreciated that the content server  22  distributes packages  12   p  without regard to any trust or security issues. As discussed below, such issues are dealt with in connection with the license server  24  and the relationship between such license server  24  and the user&#39;s computing device  14 . In one embodiment of the present invention, the content server  22  freely releases and distributes packages  12   p  having digital content  12  to any distributes requesting same. However, the content server  22  may also release and distribute such packages  12   p  in a restricted manner without departing from the spirit and scope of the present invention. For example, the content server  22  may first require payment of a pre-determined distribution fee prior to distribution, or may require that a distributes identify itself, or may indeed make a determination of whether distribution is to occur based on an identification of the distributee.  
     [0078] In addition, the content server  22  may be employed to perform inventory management by controlling the authoring tool  18  to generate a number of different packages  12   p  in advance to meet an anticipated demand. For example, the server could generate 100 packages  12   p  based on the same digital content  12 , and serve each package  12   p  10 times. As supplies of packages  12   p  dwindle to 20, for example, the content server  22  may then direct the authoring tool  18  to generate 80 additional packages  12   p,  again for example.  
     [0079] Preferably, the content server  22  in the architecture  10  has a unique public/private key pair (PU-CS, PR-CS) that is employed as part of the process of evaluating a license  16  and obtaining a decryption key (KD) for decrypting corresponding digital content  12 , as will be explained in more detail below. As is known, a public/private key pair is an asymmetric key, in that what is encrypted in one of the keys in the key pair can only be decrypted by the other of the keys in the key pair. In a public/private key pair encryption system, the public key may be made known to the world, but the private key should always be held in confidence by the owner of such private key. Accordingly, if the content server  22  encrypts data with its private key (PR-CS), it can send the encrypted data out into the world with its public key (PU-CS) for decryption purposes. Correspondingly, if an external device wants to send data to the content server  22  so that only such content server  22  can decrypt such data, such external device must first obtain the public key of the content server  22  (PU-CS) and then must encrypt the data with such public key. Accordingly, the content server  22  (and only the content server  22 ) can then employ its private key (PR-CS) to decrypt such encrypted data.  
     [0080] As with the authoring tool  18 , the content server  22  is implemented on an appropriate computer, processor, or other computing machine by way of appropriate software. The structure and operation of such machine and such software should be apparent based on the disclosure herein and therefore do not require any detailed discussion in the present disclosure. Moreover, in one embodiment of the present invention, the authoring tool  18  and the content server  22  may reside on a single computer, processor, or other computing machine, each in a separate work space. It should be recognized, moreover, that the content server  22  may in certain circumstances include the authoring tool  18  and/or perform the functions of the authoring tool  18 , as discussed above.  
     [0081] Structure of Digital Content Package  12   p    
     [0082] Referring now to FIG. 3, in one embodiment of the present invention, the digital content package  12   p  as distributed by the content server  22  includes:  
     [0083] the digital content  12  encrypted with the encryption/decryption key (KD), as was discussed above (i.e., (KD(CONTENT)));  
     [0084] the content ID (or package ID) of such digital content  12  (or package  12   p );  
     [0085] the key ID of the decryption key (KD);  
     [0086] license acquisition information, preferably in an un-encrypted form; and  
     [0087] the key KD encrypting the content server  22  public key (PU-CS), signed by the content server  22  private key (PR-CS) (i.e., (KD (PU-CS) S (PR-CS))).  
     [0088] With regard to (KD (PU-CS) S (PR-CS)), it is to be understood that such item is to be used in connection with validating the digital content  12  and/or package  12   p,  as will be explained below. Unlike a certificate with a digital signature (see below), the key (PU-CS) is not necessary to get at (KD (PU-CS)). Instead, the key (PU-CS) is obtained merely by applying the decryption key (KD). Once so obtained, such key (PU-CS) may be employed to test the validity of the signature (S (PR-CS)).  
     [0089] It should also be understood that for such package  12   p  to be constructed by the authoring tool  18 , such authoring tool  18  must already possess the license acquisition information and (KD (PU-CS) S (PR-CS)), presumably as header information supplied by the dictionary  28 . Moreover, the authoring tool  18  and the content server  22  must presumably interact to construct (KD (PU-CS) S (PR-CS)). Such interaction may for example include the steps of:  
     [0090] the content server  22  sending (PU-CS) to the authoring tool  18 ;  
     [0091] the authoring tool  18  encrypting (PU-CS) with (KD) to produce (KD (PU-CS));  
     [0092] the authoring tool  18  sending (KD (PU-CS)) to the content server  22 ;  
     [0093] the content server  22  signing (KD (PU-CS)) with (PR-CS) to produce (KD (PU-CS) S (PR-CS)); and  
     [0094] the content server  22  sending (KD (PU-CS) S (PR-CS)) to the authoring tool  18 .  
     [0095] Architecture—License Server  24   
     [0096] Referring again to FIG. 1, in one embodiment of the present invention, the license server  24  performs the functions of receiving a request for a license  16  from a user&#39;s computing device  14  in connection with a piece of digital content  12 , determining whether the user&#39;s computing device  14  can be trusted to honor an issued license  16 , negotiating such a license  16 , constructing such license  16 , and transmitting such license  16  to the user&#39;s computing device  14 . Preferably, such transmitted license  16  includes the decryption key (KD) for decrypting the digital content  12 . Such license server  24  and such functions will be explained in more detail below. Preferably, and like the content server  22 , the license server  24  in the architecture  10  has a unique public/private key pair (PU-LS, PR-LS) that is employed as part of the process of evaluating a license  16  and obtaining a decryption key (KD) for decrypting corresponding digital content  12 , as will be explained in more detail below.  
     [0097] As with the authoring tool  18  and the content server  22 , the license server  24  is implemented on an appropriate computer, processor, or other computing machine by way of appropriate software. The structure and operation of such machine and such software should be apparent based on the disclosure herein and therefore do not require any detailed discussion in the present disclosure. Moreover, in one embodiment of the present invention the authoring tool  18  and/or the content server  22  may reside on a single computer, processor, or other computing machine together with the license server  24 , each in a separate work space.  
     [0098] In one embodiment of the present invention, prior to issuance of a license  16 , the license server  24  and the content server  22  enter into an agency agreement or the like, wherein the license server  24  in effect agrees to be the licensing authority for at least a portion of the digital content  12  distributed by the content server  22 . As should be understood, one content server  22  may enter into an agency agreement or the like with several license servers  24 , and/or one license server  24  may enter into an agency agreement or the like with several content servers  22 , all without departing from the spirit and scope of the present invention.  
     [0099] Preferably, the license server  24  can show to the world that it does in fact have the authority to issue a license  16  for digital content  12  distributed by the content server  22 . To do so, it is preferable that the license server  24  send to the content server  22  the license server  24  public key (PU-LS), and that the content server  22  then send to the license server  24  a digital certificate containing PU-LS as the contents signed by the content server  22  private key (CERT (PU-LS) S (PR-CS)). As should be understood, the contents (PU-LS) in such certificate can only be accessed with the content server  22  public key (PU-CS). As should also be understood, in general, a digital signature of underlying data is an encrypted form of such data, and will not match such data when decrypted if such data has been adulterated or otherwise modified.  
     [0100] As a licensing authority in connection with a piece of digital content  12 , and as part of the licensing function, the license server  24  must have access to the decryption key (KD) for such digital content  12 . Accordingly, it is preferable that license server  24  have access to the content-key database  20  that has the decryption key (KD), key ID, and content ID (or package ID) for such digital content  12  (or package  12   p ).  
     [0101] Architecture—Black Box Server  26   
     [0102] Still referring to FIG. 1, in one embodiment of the present invention, the black box server  26  performs the functions of installing and/or upgrading a new black box  30  in a user&#39;s computing device  14 . As will be explained in more detail below, the black box  30  performs encryption and decryption functions for the user&#39;s computing device  14 . As will also be explained in more detail below, the black box  30  is intended to be secure and protected from attack. Such security and protection is provided, at least in part, by upgrading the black box  30  to a new version as necessary by way of the black box server  26 , as will be explained in more detail below.  
     [0103] As with the authoring tool  18 , the content server  22 , and the license server  24 , the black box server  26  is implemented on an appropriate computer, processor, or other computing machine by way of appropriate software. The structure and operation of such machine and such software should be apparent based on the disclosure herein and therefore do not require any detailed discussion in the present disclosure. Moreover, in one embodiment of the present invention the license server  24 , the authoring tool  18 , and/or the content server  22  may reside on a single computer, processor, or other computing machine together with the black box server  26 , each in a separate work space. Note, though, that for security purposes, it may be wise to have the black box server  26  on a separate machine.  
     [0104] Architecture—User&#39;S Computing Device  14   
     [0105] Referring now to FIG. 4, in one embodiment of the present invention, the user&#39;s computing device  14  is a personal computer or the like, having elements including a keyboard, a mouse, a screen, a processor, RAM, ROM, a hard drive, a floppy drive, a CD player, and/or the like. However, the user&#39;s computing device  14  may also be a dedicated viewing device such as a television or monitor, a dedicated audio device such as a stereo or other music player, a dedicated printer, or the like, among other things, all without departing from the spirit and scope of the present invention.  
     [0106] The content owner for a piece of digital content  12  must trust that the user&#39;s computing device  14  will abide by the rules specified by such content owner, i.e. that the digital content  12  will not be rendered unless the user obtains a license  16  that permits the rendering in the manner sought. Preferably, then, the user&#39;s computing device  14  must provide a trusted component or mechanism  32  that can satisfy to the content owner that such computing device  14  will not render the digital content  12  except according to the license rules embodied in the license  16  associated with the digital content  12  and obtained by the user.  
     [0107] Here, the trusted mechanism  32  is a Digital Rights Management (DRM) system  32  that is enabled when a user requests that a piece of digital content  12  be rendered, that determines whether the user has a license  16  to render the digital content  12  in the manner sought, that effectuates obtaining such a license  16  if necessary, that determines whether the user has the right to play the digital content  12  according to the license  16 , and that decrypts the digital content  12  for rendering purposes if in fact the user has such right according to such license  16 . The contents and function of the DRM system  32  on the user&#39;s computing device  14  and in connection with the architecture  10  are described below.  
     [0108] DRM System  32   
     [0109] The DRM system  32  performs four main functions with the architecture  10  disclosed herein: (1) content acquisition, (2) license acquisition, (3) content rendering, and (4) black box  30  installation/update. Preferably, any of the functions can be performed at any time, although it is recognized that some of the functions already require that digital content  12  be acquired.  
     [0110] DRM System  32 —Content Acquisition  
     [0111] Acquisition of digital content  12  by a user and/or the user&#39;s computing device  14  is typically a relatively straight-forward matter and generally involves placing a file having encrypted digital content  12  on the user&#39;s computing device  14 . Of course, to work with the architecture  10  and the DRM system  32  disclosed herein, it is necessary that the encrypted digital content  12  be in a form that is amenable to such architecture  10  and DRM system  32 , such as the digital package  12   p  as will be described below.  
     [0112] As should be understood, the digital content  12  may be obtained in any manner from a content server  22 , either directly or indirectly, without departing from the spirit and scope of the present invention. For example, such digital content  12  may be downloaded from a network such as the Internet, located on an obtained optical or magnetic disk or the like, received as part of an E-mail message or the like, or downloaded from an electronic bulletin board or the like.  
     [0113] Such digital content  12 , once obtained, is preferably stored in a manner such that the obtained digital content  12  is accessible by a rendering application  34  (to be described below) running on the computing device  14 , and by the DRM system  32 . For example, the digital content  12  may be placed as a file on a hard drive (not shown) of the user&#39;s computing device  14 , or on a network server (not shown) accessible to the computing device  14 . In the case where the digital content  12  is obtained on an optical or magnetic disk or the like, it may only be necessary that such disk be present in an appropriate drive (not shown) coupled to the user&#39;s computing device  14 .  
     [0114] In the present invention, it is not envisioned that any special tools are necessary to acquire digital content  12 , either from the content server  22  as a direct distribution source or from some intermediary as an indirect distribution source. That is, it is preferable that digital content  12  be as easily acquired as any other data file. However, the DRM system  32  and/or the rendering application  34  may include an interface (not shown) designed to assist the user in obtaining digital content  12 . For example, the interface may include a web browser especially designed to search for digital content  12 , links to pre-defined Internet web sites that are known to be sources of digital content  12 , and the like.  
     [0115] DRM System  32 —Content Rendering, Part 1  
     [0116] Referring now to FIG. 5A, in one embodiment of the present invention, assuming the encrypted digital content  12  has been distributed to and received by a user and placed by the user on the computing device  14  in the form of a stored file, the user will attempt to render the digital content  12  by executing some variation on a render command (step  501 ). For example, such render command may be embodied as a request to ‘play’ or ‘open’ the digital content  12 . In some computing environments, such as for example the “MICROSOFT WINDOWS” operating system, distributed by MICROSOFT Corporation of Redmond, Washington, such play or open command may be as simple as ‘clicking’ on an icon representative of the digital content  12 . Of course, other embodiments of such render command may be employed without departing from the spirit and scope of the present invention. In general, such render command may be considered to be executed whenever a user directs that a file having digital content  12  be opened, run, executed, and/or the like.  
     [0117] Importantly, and in addition, such render command may be embodied as a request to copy the digital content  12  to another form, such as to a printed form, a visual form, an audio form, etc. As should be understood, the same digital content  12  may be rendered in one form, such as on a computer screen, and then in another form, such as a printed document. In the present invention, each type of rendering is performed only if the user has the right to do so, as will be explained below.  
     [0118] In one embodiment of the present invention, the digital content  12  is in the form of a digital file having a file name ending with an extension, and the computing device  14  can determine based on such extension to start a particular kind of rendering application  34 . For example, if the file name extension indicates that the digital content  12  is a text file, the rendering application  34  is some form of word processor such as the “MICROSOFT WORD”, distributed by MICROSOFT Corporation of Redmond, Washington. Likewise, if the file name extension indicates that the digital content  12  is an audio, video, and/or multimedia file, the rendering application  34  is some form of multimedia player, such as “MICROSOFT MEDIA PLAYER”, also distributed by MICROSOFT Corporation of Redmond, Wash.  
     [0119] Of course, other methods of determining a rendering application may be employed without departing from the spirit and scope of the present invention. As but one example, the digital content  12  may contain meta-data in an un-encrypted form (i.e., the aforementioned header information), where the meta-data includes information on the type of rendering application  34  necessary to render such digital content  12 .  
     [0120] Preferably, such rendering application  34  examines the digital content  12  associated with the file name and determines whether such digital content  12  is encrypted in a rights-protected form (steps  503 ,  505 ). If not protected, the digital content  12  may be rendered without further ado (step  507 ). If protected, the rendering application  34  determines from the encrypted digital content  12  that the DRM system  32  is necessary to play such digital content  12 . Accordingly, such rendering application  34  directs the user&#39;s computing device  14  to run the DRM system  32  thereon (step  509 ). Such rendering application  34  then calls such DRM system  32  to decrypt the digital content  12  (step  511 ). As will be discussed in more detail below, the DRM system  32  in fact decrypts the digital content  12  only if the user has a valid license  16  for such digital content  12  and the right to play the digital content  12  according to the license rules in the valid license  16 . Preferably, once the DRM system  32  has been called by the rendering application  34 , such DRM system  32  assumes control from the rendering application  34 , at least for purposes of determining whether the user has a right to play such digital content  12  (step  513 ).  
     [0121] DRM System  32  Components  
     [0122] In one embodiment of the present invention, and referring again to FIG. 4, the DRM system  32  includes a license evaluator  36 , the black box  30 , a license store  38 , and a state store  40 .  
     [0123] DRM System  32  Components—License Evaluator  36   
     [0124] The license evaluator  36  locates one or more licenses  16  that correspond to the requested digital content  12 , determines whether such licenses  16  are valid, reviews the license rules in such valid licenses  16 , and determines based on the reviewed license rules whether the requesting user has the right to render the requested digital content  12  in the manner sought, among other things. As should be understood, the license evaluator  36  is a trusted component in the DRM system  32 . In the present disclosure, to be ‘trusted’ means that the license server  24  (or any other trusting element) is satisfied that the trusted element will carry out the wishes of the owner of the digital content  12  according to the rights description in the license  16 , and that a user cannot easily alter such trusted element for any purpose, nefarious or otherwise.  
     [0125] The license evaluator  36  has to be trusted in order to ensure that such license evaluator  36  will in fact evaluate a license  16  properly, and to ensure that such license evaluator  36  has not been adulterated or otherwise modified by a user for the purpose of bypassing actual evaluation of a license  16 . Accordingly, the license evaluator  36  is run in a protected or shrouded environment such that the user is denied access to such license evaluator  36 . Other protective measures may of course be employed in connection with the license evaluator  36  without departing from the spirit and scope of the present invention.  
     [0126] DRM System  32  Components—Black Box  30   
     [0127] Primarily, and as was discussed above, the black box  30  performs encryption and decryption functions in the DRM system  32 . In particular, the black box  30  works in conjunction with the license evaluator  36  to decrypt and encrypt certain information as part of the license evaluation function. In addition, once the license evaluator  36  determines that a user does in fact have the right to render the requested digital content  12  in the manner sought, the black box  30  is provided with a decryption key (KD) for such digital content  12 , and performs the function of decrypting such digital content  12  based on such decryption key (KD).  
     [0128] The black box  30  is also a trusted component in the DRM system  32 . In particular, the license server  24  must trust that the black box  30  will perform the decryption function only in accordance with the license rules in the license  16 , and also trust that such black box  30  will not operate should it become adulterated or otherwise modified by a user for the nefarious purpose of bypassing actual evaluation of a license  16 . Accordingly, the black box  30  is also run in a protected or shrouded environment such that the user is denied access to such black box  30 . Again, other protective measures may be employed in connection with the black box  30  without departing from the spirit and scope of the present invention. Preferably, and like the content server  22  and license server  24 , the black box  30  in the DRM system  32  has a unique public/private key pair (PU-BB, PR-BB) that is employed as part of the process of evaluating the license  16  and obtaining a decryption key (KD) for decrypting the digital content  12 , as will be described in more detail below.  
     [0129] DRM System  32  Components—License Store  38   
     [0130] The license store  38  stores licenses  16  received by the DRM system  32  for corresponding digital content  12 . The license store  38  itself need not be trusted since the license store  38  merely stores licenses  16 , each of which already has trust components built thereinto, as will be described below. In one embodiment of the present invention, the license store  38  is merely a sub-directory of a drive such as a hard disk drive or a network drive. However, the license store  38  may be embodied in any other form without departing from the spirit and scope of the present invention, so long as such license store  38  performs the function of storing licenses  16  in a location relatively convenient to the DRM system  32 .  
     [0131] DRM System  32  Components—State Store  40   
     [0132] The state store  40  performs the function of maintaining state information corresponding to licenses  16  presently or formerly in the license store  38 . Such state information is created by the DRM system  32  and stored in the state store  40  as necessary. For example, if a particular license  16  only allows a pre-determined number of renderings of a piece of corresponding digital content  12 , the state store  40  maintains state information on how many renderings have in fact taken place in connection with such license  16 . The state store  40  continues to maintain state information on licenses  16  that are no longer in the license store  38  to avoid the situation where it would otherwise be advantageous to delete a license  16  from the license store  38  and then obtain an identical license  16  in an attempt to delete the corresponding state information from the state store  40 .  
     [0133] The state store  40  also has to be trusted in order to ensure that the information stored therein is not reset to a state more favorable to a user. Accordingly, the state store  40  is likewise run in a protected or shrouded environment such that the user is denied access to such state store  40 . Once again, other protective measures may of course be employed in connection with the state store  40  without departing from the spirit and scope of the present invention. For example, the state store  40  may be stored by the DRM system  32  on the computing device  14  in an encrypted form.  
     [0134] DRM System  32 —Content Rendering, Part 2  
     [0135] Referring again to FIG. 5A, and again discussing content rendering in one embodiment of the present invention, once the DRM system  32  has assumed control from the calling rendering application  34 , such DRM system  32  then begins the process of determining whether the user has a right to render the requested digital content  12  in the manner sought. In particular, the DRM system  32  either locates a valid, enabling license  16  in the license store (steps  515 ,  517 ) or attempts to acquire a valid, enabling license  16  from the license server  24  (i.e. performs the license acquisition function as discussed below and as shown in FIG. 7).  
     [0136] As a first step, and referring now to FIG. 6, the license evaluator  36  of such DRM system  32  checks the license store  38  for the presence of one or more received licenses  16  that correspond to the digital content  12  (step  601 ). Typically, the license  16  is in the form of a digital file, as will be discussed below, although it will be recognized that the license  16  may also be in other forms without departing from the spirit and scope of the present invention. Typically, the user will receive the digital content  12  without such license  16 , although it will likewise be recognized that the digital content  12  may be received with a corresponding license  16  without departing from the spirit and scope of the present invention.  
     [0137] As was discussed above in connection with FIG. 3, each piece of digital content  12  is in a package  12   p  with a content ID (or package ID) identifying such digital content  12  (or package  12   p ), and a key ID identifying the decryption key (KD) that will decrypt the encrypted digital content  12 . Preferably, the content ID (or package ID) and the key ID are in an un-encrypted form. Accordingly, and in particular, based on the content ID of the digital content  12 , the license evaluator  36  looks for any license  16  in the license store  38  that contains an identification of applicability to such content ID. Note that multiple such licenses  16  may be found, especially if the owner of the digital content  12  has specified several different kinds of licenses  16  for such digital content  12 , and the user has obtained multiple ones of such licenses  16 . If in fact the license evaluator  36  does not find in the license store  38  any license  16  corresponding to the requested digital content  12 , the DRM system  32  may then perform the function of license acquisition (step  519  of FIG. 5), to be described below.  
     [0138] Assume now that the DRM system  32  has been requested to render a piece of digital content  12 , and one or more licenses  16  corresponding thereto are present in the license store  38 . In one embodiment of the present invention, then, the license evaluator  36  of the DRM system  32  proceeds to determine for each such license  16  whether such license  16  itself is valid (steps  603  and  605  of FIG. 6). Preferably, and in particular, each license  16  includes a digital signature  26  based on the content  28  of the license  16 . As should be understood, the digital signature  26  will not match the license  16  if the content  28  has been adulterated or otherwise modified. Thus, the license evaluator  36  can determine based on the digital signature  26  whether the content  28  is in the form that it was received from the license server  24  (i.e., is valid). If no valid license  16  is found in the license store  38 , the DRM system  32  may then perform the license acquisition function described below to obtain such a valid license  16 .  
     [0139] Assuming that one or more valid licenses  16  are found, for each valid license  16 , the license evaluator  36  of the DRM system  32  next determines whether such valid license  16  gives the user the right to render the corresponding digital content  12  in the manner desired (i.e., is enabling) (steps  607  and  609 ). In particular, the license evaluator  36  determines whether the requesting user has the right to play the requested digital content  12  based on the rights description in each license  16  and based on what the user is attempting to do with the digital content  12 . For example, such rights description may allow the user to render the digital content  12  into a sound, but not into a decrypted digital copy.  
     [0140] As should be understood, the rights description in each license  16  specifies whether the user has rights to play the digital content  12  based on any of several factors, including who the user is, where the user is located, what type of computing device  14  the user is using, what rendering application  34  is calling the DRM system  32 , the date, the time, etc. In addition, the rights description may limit the license  16  to a pre-determined number of plays, or pre-determined play time, for example. In such case, the DRM system  32  must refer to any state information with regard to the license  16 , (i.e., how many times the digital content  12  has been rendered, the total amount of time the digital content  12  has been rendered, etc.), where such state information is stored in the state store  40  of the DRM system  32  on the user&#39;s computing device  14 .  
     [0141] Accordingly, the license evaluator  36  of the DRM system  32  reviews the rights description of each valid license  16  to determine whether such valid license  16  confers the rights sought to the user. In doing so, the license evaluator  36  may have to refer to other data local to the user&#39;s computing device  14  to perform a determination of whether the user has the rights sought. As seen in FIG. 4, such data may include an identification  42  of the user&#39;s computing device (machine)  14  and particular aspects thereof, an identification  44  of the user and particular aspects thereof, an identification of the rendering application  34  and particular aspects thereof, a system clock  46 , and the like. If no valid license  16  is found that provides the user with the right to render the digital content  12  in the manner sought, the DRM system  32  may then perform the license acquisition function described below to obtain such a license  16 , if in fact such a license  16  is obtainable.  
     [0142] Of course, in some instances the user cannot obtain the right to render the digital content  12  in the manner requested, because the content owner of such digital content  12  has in effect directed that such right not be granted. For example, the content owner of such digital content  12  may have directed that no license  16  be granted to allow a user to print a text document, or to copy a multimedia presentation into an un-encrypted form. In one embodiment of the present invention, the digital content  12  includes data on what rights are available upon purchase of a license  16 , and types of licenses  16  available. However, it will be recognized that the content owner of a piece of digital content  12  may at any time change the rights currently available for such digital content  12  by changing the licenses  16  available for such digital content  12 .  
     [0143] DRM System  32 —License Acquisition  
     [0144] Referring now to FIG. 7, if in fact the license evaluator  36  does not find in the license store  38  any valid, enabling license  16  corresponding to the requested digital content  12 , the DRM system  32  may then perform the function of license acquisition. As shown in FIG. 3, each piece of digital content  12  is packaged with information in an un-encrypted form regarding how to obtain a license  16  for rendering such digital content  12  (i.e., license acquisition information).  
     [0145] In one embodiment of the present invention, such license acquisition information may include (among other things) types of licenses  16  available, and one or more Internet web sites or other site information at which one or more appropriate license servers  24  may be accessed, where each such license server  24  is in fact capable of issuing a license  16  corresponding to the digital content  12 . Of course, the license  16  may be obtained in other manners without departing from the spirit and scope of the present invention. For example, the license  16  may be obtained from a license server  24  at an electronic bulletin board, or even in person or via regular mail in the form of a file on a magnetic or optical disk or the like.  
     [0146] Assuming that the location for obtaining a license  16  is in fact a license server  24  on a network, the license evaluator  36  then establishes a network connection to such license server  24  based on the web site or other site information, and then sends a request for a license  16  from such connected license server  24  (steps  701 ,  703 ). In particular, once the DRM system  32  has contacted the license server  24 , such DRM system  32  transmits appropriate license request information  36  to such license server  24 . In one embodiment of the present invention, such license  16  request information  36  may include:  
     [0147] the public key of the black box  30  of the DRM system  32  (PU-BB);  
     [0148] the version number of the black box  30  of the DRM system  32 ;  
     [0149] a certificate with a digital signature from a certifying authority certifying the black box  30  (where the certificate may in fact include the aforementioned public key and version number of the black box  30 );  
     [0150] the content ID (or package ID) that identifies the digital content  12  (or package  12   p );  
     [0151] the key ID that identifies the decryption key (KD) for decrypting the digital content  12 ;  
     [0152] the type of license  16  requested (if in fact multiple types are available);  
     [0153] the type of rendering application  34  that requested rendering of the digital content  12 ;  
     [0154] and/or the like, among other things. Of course, greater or lessor amounts of license  16  request information  36  may be transmitted to the license server  24  by the DRM system  32  without departing from the spirit and scope of the present invention. For example, information on the type of rendering application  34  may not be necessary, while additional information about the user and/or the user&#39;s computing device  14  may be necessary.  
     [0155] Once the license server  24  has received the license  16  request information  36  from the DRM system  32 , the license server  24  may then perform several checks for trust/authentication and for other purposes. In one embodiment of the present invention, such license server  24  checks the certificate with the digital signature of the certifying authority to determine whether such has been adulterated or otherwise modified (steps  705 ,  707 ). If so, the license server  24  refuses to grant any license  16  based on the request information  36 . The license server  24  may also maintain a list of known ‘bad’ users and/or user&#39;s computing devices  14 , and may refuse to grant any license  16  based on a request from any such bad user and/or bad user&#39;s computing device  14  on the list. Such ‘bad’ list may be compiled in any appropriate manner without departing from the spirit and scope of the present invention.  
     [0156] Based on the received request and the information associated therewith, and particularly based on the content ID (or package ID) in the license request information, the license server  24  can interrogate the content-key database  20  (FIG. 1) and locate a record corresponding to the digital content  12  (or package  12   p ) that is the basis of the request. As was discussed above, such record contains the decryption key (KD), key ID, and content ID for such digital content  12 . In addition, such record may contain license data regarding the types of licenses  16  to be issued for the digital content  12  and the terms and conditions for each type of license  16 . Alternatively, such record may include a pointer, link, or reference to a location having such additional information.  
     [0157] As mentioned above, multiple types of licenses  16  may be available. For example, for a relatively small license fee, a license  16  allowing a limited number of renderings may be available. For a relatively greater license fee, a license  16  allowing unlimited renderings until an expiration date may be available. For a still greater license fee, a license  16  allowing unlimited renderings without any expiration date may be available. Practically any type of license  16  having any kind of license terms may be devised and issued by the license server  24  without departing from the spirit and scope of the present invention.  
     [0158] In one embodiment of the present invention, the request for a license  16  is accomplished with the aid of a web page or the like as transmitted from the license server  24  to the user&#39;s computing device  14 . Preferably, such web page includes information on all types of licenses  16  available from the license server  24  for the digital content  12  that is the basis of the license  16  request.  
     [0159] In one embodiment of the present invention, prior to issuing a license  16 , the license server  24  checks the version number of the black box  30  to determine whether such black box  30  is relatively current (steps  709 ,  711 ). As should be understood, the black box  30  is intended to be secure and protected from attacks from a user with nefarious purposes (i.e., to improperly render digital content  12  without a license  16 , or outside the terms of a corresponding license  16 ). However, it is to be recognized that no system and no software device is in fact totally secure from such an attack.  
     [0160] As should also be understood, if the black box  30  is relatively current, i.e., has been obtained or updated relatively recently, it is less likely that such black box  30  has been successfully attacked by such a nefarious user. Preferably, and as a matter of trust, if the license server  24  receives a license request with request information  36  including a black box  30  version number that is not relatively current, such license server  24  refuses to issue the requested license  16  until the corresponding black box  30  is upgraded to a current version, as will be described below. Put simply, the license server  24  will not trust such black box  30  unless such black box  30  is relatively current.  
     [0161] In the context of the black box  30  of the present invention, the term ‘current’ or ‘relatively current’ may have any appropriate meaning without departing from the spirit and scope of the present invention, consistent with the function of providing trust in the black box  30  based on the age or use thereof. For example, ‘current’ may be defined according to age (i.e., less than one month old). As an alternative example, ‘current’ may be defined based on a number of times that the black box  30  has decrypted digital content  12  (i.e., less than 200 instances of decryption). Moreover, ‘current’ may be based on policy as set by each license server  24 , where one license server  24  may define ‘current’ differently from another license server  24 , and a license server  24  may further define ‘current’ differently depending on the digital content  12  for which a license  16  is requested, or depending on the type of license  16  requested, among other things.  
     [0162] Assuming that the license server  24  is satisfied from the version number of a black box  30  or other indicia thereof that such black box  30  is current, the license server  24  then proceeds to negotiate terms and conditions for the license  16  with the user (step  713 ). Alternatively, the license server  24  negotiates the license  16  with the user, then satisfies itself from the version number of the black box  30  that such black box  30  is current (i.e., performs step  713 , then step  711 ). Of course, the amount of negotiation varies depending on the type of license  16  to be issued, and other factors. For example, if the license server  24  is merely issuing a paid-up unlimited use license  16 , very little need be negotiated. On the other hand, if the license  16  is to be based on such items as varying values, sliding scales, break points, and other details, such items and details may need to be worked out between the license server  24  and the user before the license  16  can be issued.  
     [0163] As should be understood, depending on the circumstances, the license negotiation may require that the user provide further information to the license server  24  (for example, information on the user, the user&#39;s computing device  14 , etc.). Importantly, the license negotiation may also require that the user and the license server  24  determine a mutually acceptable payment instrument (a credit account, a debit account, a mailed check, etc.) and/or payment method (paid-up immediately, spread over a period of time, etc.), among other things.  
     [0164] Once all the terms of the license  16  have been negotiated and agreed to by both the license server  24  and user (step  715 ), a digital license  16  is generated by the license server  24  (step  719 ), where such generated license  16  is based at least in part on the license request, the black box  30  public key (PU-BB), and the decryption key (KD) for the digital content  12  that is the basis of the request as obtained from the content-key database  20 . In one embodiment of the present invention, and as seen in FIG. 8, the generated license  16  includes:  
     [0165] the content ID of the digital content  12  to which the license  16  applies;  
     [0166] a Digital Rights License (DRL)  48  (i.e., the rights description or actual terms and conditions of the license  16  written in a predetermined form that the license evaluator  36  can interrogate), perhaps encrypted with the decryption key (KD) (i.e., KD (DRL));  
     [0167] the decryption key (KD) for the digital content  12  encrypted with the black box  30  public key (PU-BB) as receive in the license request (i.e.,(PU-BB (KD));  
     [0168] a digital signature from the license server  24  (without any attached certificate) based on (KD (DRL)) and (PU-BB (KD)) and encrypted with the license server  24  private key (i.e., (S (PR-LS))); and  
     [0169] the certificate that the license server  24  obtained previously from the content server  22 , such certificate indicating that the license server  24  has the authority from the content server  22  to issue the license  16  (i.e., (CERT (PU-LS) S (PR-CS))).  
     [0170] As should be understood, the aforementioned elements and perhaps others are packaged into a digital file or some other appropriate form. As should also be understood, if the DRL  48  or (PU-BB (KD)) in the license  16  should become adulterated or otherwise modified, the digital signature (S (PR-LS)) in the license  16  will not match and therefore will not validate such license  16 . For this reason, the DRL  48  need not necessarily be in an encrypted form (i.e., (KD(DRL)) as mentioned above), although such encrypted form may in some instances be desirable and therefore may be employed without departing from the spirit and scope of the present invention.  
     [0171] Once the digital license  16  has been prepared, such license  16  is then issued to the requestor (i.e., the DRM system  32  on the user&#39;s computing device  14 ) (step  719  of FIG. 7). Preferably, the license  16  is transmitted over the same path through which the request therefor was made (i.e., the Internet or another network), although another path may be employed without departing from the spirit and scope of the present invention. Upon receipt, the requesting DRM system  32  preferably automatically places the received digital license  16  in the license store  38  (step  721 ).  
     [0172] It is to be understood that a user&#39;s computing device  14  may on occasion malfunction, and licenses  16  stored in the license store  38  of the DRM system  32  on such user&#39;s computing device  14  may become irretrievably lost. Accordingly, it is preferable that the license server  24  maintain a database  50  of issued licenses  16  (FIG. 1), and that such license server  24  provide a user with a copy or re-issue (hereinafter ‘re-issue’) of an issued license  16  if the user is in fact entitled to such re-issue. In the aforementioned case where licenses  16  are irretrievably lost, it is also likely the case that state information stored in the state store  40  and corresponding to such licenses  16  is also lost. Such lost state information should be taken into account when re-issuing a license  16 . For example, a fixed number of renderings license  16  might legitimately be re-issued in a pro-rated form after a relatively short period of time, and not re-issued at all after a relatively longer period of time.  
     [0173] DRM System  32 —Installation/Upgrade of Black Box  30   
     [0174] As was discussed above, as part of the function of acquiring a license  16 , the license server  24  may deny a request for a license  16  from a user if the user&#39;s computing device  14  has a DRM system  32  with a black box  30  that is not relatively current, i.e., has a relatively old version number. In such case, it is preferable that the black box  30  of such DRM system  32  be upgraded so that the license acquisition function can then proceed. Of course, the black box  30  may be upgraded at other times without departing from the spirit and scope of the present invention.  
     [0175] Preferably, as part of the process of installing the DRM system  32  on a user&#39;s computing device  14 , a non-unique ‘lite’ version of a black box  30  is provided. Such ‘lite’ black box  30  is then upgraded to a unique regular version prior to rendering a piece of digital content  12 . As should be understood, if each black box  30  in each DRM system  32  is unique, a security breach into one black box  30  cannot easily be replicated with any other black box  30 .  
     [0176] Referring now to FIG. 9, the DRM system  32  obtains the unique black box  30  by requesting same from a black box server  26  or the like (as was discussed above and as shown in FIG. 1) (step  901 ). Typically, such request is made by way of the Internet, although other means of access may be employed without departing from the spirit and scope of the present invention. For example, the connection to a black box server  26  may be a direct connection, either locally or remotely. An upgrade from one unique non-lite black box  30  to another unique non-lite black box  30  may also be requested by the DRM system  32  at any time, such as for example a time when a license server  24  deems the black box  30  not current, as was discussed above.  
     [0177] Thereafter, the black box server  26  generates a new unique black box  30  (step  903 ). As seen in FIG. 3, each new black box  30  is provided with a version number and a certificate with a digital signature from a certifying authority. As was discussed above in connection with the license acquisition function, the version number of the black box  30  indicates the relative age and/or use thereof. The certificate with the digital signature from the certifying authority, also discussed above in connection with the license acquisition function, is a proffer or vouching mechanism from the certifying authority that a license server  24  should trust the black box  30 . Of course, the license server  24  must trust the certifying authority to issue such a certificate for a black box  30  that is in fact trustworthy. It may be the case, in fact, that the license server  24  does not trust a particular certifying authority, and refuses to honor any certificate issued by such certifying authority. Trust may not occur, for example, if a particular certifying authority is found to be engaging in a pattern of improperly issuing certificates.  
     [0178] Preferably, and as was discussed above, the black box server  26  includes a new unique public/private key pair (PU-BB, PR-BB) with the newly generated unique black box  30  (step  903  of FIG. 9). Preferably, the private key for the black box  30  (PR-BB) is accessible only to such black box  30 , and is hidden from and inaccessible by the remainder of the world, including the computing device  14  having the DRM system  32  with such black box  30 , and the user thereof.  
     [0179] Most any hiding scheme may be employed without departing from the spirit and scope of the present invention, so long as such hiding scheme in fact performs the function of hiding the private key (PR-BB) from the world. As but one example, the private key (PR-BB) may be split into several sub-components, and each sub-component may be encrypted uniquely and stored in a different location. In such a situation, it is preferable that such sub-components are never assembled in full to produce the entire private key (PR-BB).  
     [0180] In one embodiment of the present invention, such private key (PR-BB) is encrypted according to code-based encryption techniques. In particular, in such embodiment, the actual software code of the black box  30  (or other software code) is employed as encrypting key(s). Accordingly, if the code of the black box  30  (or the other software code) becomes adulterated or otherwise modified, for example by a user with nefarious purposes, such private key (PR-BB) cannot be decrypted.  
     [0181] Although each new black box  30  is delivered with a new public/private key pair (PU-BB, PR-BB), such new black box  30  is also preferably given access to old public/private key pairs from old black boxes  30  previously delivered to the DRM system  32  on the user&#39;s computing device  14  (step  905 ). Accordingly, the upgraded black box  30  can still employ the old key pairs to access older digital content  12  and older corresponding licenses  16  that were generated according to such old key pairs, as will be discussed in more detail below.  
     [0182] Preferably, the upgraded black box  30  delivered by the black box server  26  is tightly tied to or associated with the user&#39;s computing device  14 . Accordingly, the upgraded black box  30  cannot be operably transferred among multiple computing devices  14  for nefarious purposes or otherwise. In one embodiment of the present invention, as part of the request for the black box  30  (step  901 ) the DRM system  32  provides hardware information unique to such DRM system  32  and/or unique to the user&#39;s computing device  14  to the black box server  26 , and the black box server  26  generates a black box  30  for the DRM system  32  based in part on such provided hardware information. Such generated upgraded black box  30  is then delivered to and installed in the DRM system  32  on the user&#39;s computing device  14  (steps  907 ,  909 ). If the upgraded black box  30  is then somehow transferred to another computing device  14 , the transferred black box  30  recognizes that it is not intended for such other computing device  14 , and does not allow any requested rendering to proceed on such other computing device  14 .  
     [0183] Once the new black box  30  is installed in the DRM system  32 , such DRM system  32  can proceed with a license acquisition function or with any other function.  
     [0184] DRM System  32 —Content Rendering, Part 3  
     [0185] Referring now to FIG. 5B, and assuming, now, that the license evaluator  36  has found at least one valid license  16  and that at least one of such valid licenses  16  provides the user with the rights necessary to render the corresponding digital content  12  in the manner sought (i.e., is enabling), the license evaluator  36  then selects one of such licenses  16  for further use (step  519 ). Specifically, to render the requested digital content  12 , the license evaluator  36  and the black box  30  in combination obtain the decryption key (KD) from such license  16 , and the black box  30  employs such decryption key (KD) to decrypt the digital content  12 . In one embodiment of the present invention, and as was discussed above, the decryption key (KD) as obtained from the license  16  is encrypted with the black box  30  public key (PU-BB(KD)), and the black box  30  decrypts such encrypted decryption key with its private key (PR-BB) to produce the decryption key (KD) (steps  521 ,  523 ). However, other methods of obtaining the decryption key (KD) for the digital content  12  may be employed without departing from the spirit and scope of the present invention.  
     [0186] Once the black box  30  has the decryption key (KD) for the digital content  12  and permission from the license evaluator  36  to render the digital content  12 , control may be returned to the rendering application  34  (steps  525 ,  527 ). In one embodiment of the present invention, the rendering application  34  then calls the DRM system  32 /black box  30  and directs at least a portion of the encrypted digital content  12  to the black box  30  for decryption according to the decryption key (KD) (step  529 ). The black box  30  decrypts the digital content  12  based upon the decryption key (KD) for the digital content  12 , and then the black box  30  returns the decrypted digital content  12  to the rendering application  34  for actual rendering (steps  533 ,  535 ). The rendering application  34  may either send a portion of the encrypted digital content  12  or the entire digital content  12  to the black box  30  for decryption based on the decryption key (KD) for such digital content  12  without departing from the spirit and scope of the present invention.  
     [0187] Preferably, when the rendering application  34  sends digital content  12  to the black box  30  for decryption, the black box  30  and/or the DRM system  32  authenticates such rendering application  34  to ensure that it is in fact the same rendering application  34  that initially requested the DRM system  32  to run (step  531 ). Otherwise, the potential exists that rendering approval may be obtained improperly by basing the rendering request on one type of rendering application  34  and in fact rendering with another type of rendering application  34 . Assuming the authentication is successful and the digital content  12  is decrypted by the black box  30 , the rendering application  34  may then render the decrypted digital content  12  (steps  533 ,  535 ).  
     [0188] Sequence of Key Transactions  
     [0189] Referring now to FIG. 10, in one embodiment of the present invention, a sequence of key transactions is performed to obtain the decryption key (KD) and evaluate a license  16  for a requested piece of digital content  12  (i.e., to perform steps  515 - 523  of FIGS. 5A and 5B). Mainly, in such sequence, the DRM system  32  obtains the decryption key (KD) from the license  16 , uses information obtained from the license  16  and the digital content  12  to authenticate or ensure the validity of both, and then determines whether the license  16  in fact provides the right to render the digital content  12  in the manner sought. If so, the digital content  12  may be rendered.  
     [0190] Bearing in mind that each license  16  for the digital content  12 , as seen in FIG. 8, includes:  
     [0191] the content ID of the digital content  12  to which the license  16  applies;  
     [0192] the Digital Rights License (DRL)  48 , perhaps encrypted with the decryption key (KD) (i.e., KD (DRL));  
     [0193] the decryption key (KD) for the digital content  12  encrypted with the black box  30  public key (PU-BB) (i.e.,(PU-BB (KD));  
     [0194] the digital signature from the license server  24  based on (KD (DRL)) and (PU-BB (KD)) and encrypted with the license server  24  private key (i.e., (S (PR-LS))); and  
     [0195] the certificate that the license server  24  obtained previously from the content server  22  (i.e., (CERT (PU-LS) S (PR-CS))),  
     [0196] and also bearing in mind that the package  12   p  having the digital content  12 , as seen in FIG. 3, includes:  
     [0197] the content ID of such digital content  12 ;  
     [0198] the digital content  12  encrypted by KD (i.e., (KD(CONTENT)));  
     [0199] a license acquisition script that is not encrypted; and  
     [0200] the key KD encrypting the content server  22  public key (PU-CS), signed by the content server  22  private key (PR-CS) (i.e., (KD (PU-CS) S (PR-CS))),  
     [0201] in one embodiment of the present invention, the specific sequence of key transactions that are performed with regard to a specific one of the licenses  16  for the digital content  12  is as follows:  
     [0202] 1. Based on (PU-BB (KD)) from the license  16 , the black box  30  of the DRM system  32  on the user&#39;s computing device  14  applies its private key (PR-BB) to obtain (KD) (step  1001 ). (PR-BB (PU-BB (KD))=(KD)). Note, importantly, that the black box  30  could then proceed to employ KD to decrypt the digital content  12  without any further ado. However, and also importantly, the license server  24  trusts the black box  30  not to do so. Such trust was established at the time such license server  24  issued the license  16  based on the certificate from the certifying authority vouching for the trustworthiness of such black box  30 . Accordingly, despite the black box  30  obtaining the decryption key (KD) as an initial step rather than a final step, the DRM system  32  continues to perform all license  16  validation and evaluation functions, as described below.  
     [0203] 2. Based on (KD (PU-CS) S (PR-CS)) from the digital content  12 , the black box  30  applies the newly obtained decryption key (KD) to obtain (PU-CS) (step  1003 ). (KD (KD (PU-CS)) =(PU-CS)). Additionally, the black box  30  can apply (PU-CS) as against the signature (S (PR-CS)) to satisfy itself that such signature and such digital content  12 /package  12   p  is valid (step  1005 ). If not valid, the process is halted and access to the digital content  12  is denied.  
     [0204] 3. Based on (CERT (PU-LS) S (PR-CS)) from the license  16 , the black box  30  applies the newly obtained content server  22  public key (PU-CS) to satisfy itself that the certificate is valid (step  1007 ), signifying that the license server  24  that issued the license  16  had the authority from the content server  22  to do so, and then examines the certificate contents to obtain (PU-LS) (step  1009 ). If not valid, the process is halted and access to the digital content  12  based on the license  16  is denied.  
     [0205] 4. Based on (S (PR-LS)) from the license  16 , the black box  30  applies the newly obtained license server  24  public key (PU-LS) to satisfy itself that the license  16  is valid (step  1011 ). If not valid, the process is halted and access to the digital content  12  based on the license  16  is denied.  
     [0206] 5. Assuming all validation steps are successful, and that the DRL  48  in the license  16  is in fact encrypted with the decryption key (KD), the license evaluator  36  then applies the already-obtained decryption key (KD) to (KD(DRL)) as obtained from the license  16  to obtain the license terms from the license  16  (i.e., the DRL  48 ) (step  1013 ). Of course, if the DRL  48  in the license  16  is not in fact encrypted with the decryption key (KD), step  1013  may be omitted. The license evaluator  36  then evaluates/interrogates the DRL  48  and determines whether the user&#39;s computing device  14  has the right based on the DRL  48  in the license  16  to render the corresponding digital content  12  in the manner sought (i.e., whether the DRL  48  is enabling) (step  1015 ). If the license evaluator  36  determines that such right does not exist, the process is halted and access to the digital content  12  based on the license  16  is denied.  
     [0207] 6. Finally, assuming evaluation of the license  16  results in a positive determination that the user&#39;s computing device  14  has the right based on the DRL  48  terms to render the corresponding digital content  12  in the manner sought, the license evaluator  36  informs the black box  30  that such black box  30  can render the corresponding digital content  12  according to the decryption key (KD). The black box  30  thereafter applies the decryption key (KD) to decrypt the digital content  12  from the package  12   p  (i.e., (KD(KD(CONTENT))=(CONTENT)) (step  1017 ).  
     [0208] It is important to note that the above-specified series of steps represents an alternating or ‘ping-ponging’ between the license  16  and the digital content  12 . Such ping-ponging ensures that the digital content  12  is tightly bound to the license  16 , in that the validation and evaluation process can only occur if both the digital content  12  and license  16  are present in a properly issued and valid form. In addition, since the same decryption key (KD) is needed to get the content server  22  public key (PU-CS) from the license  16  and the digital content  12  from the package  12   p  in a decrypted form (and perhaps the license terms (DRL  48 ) from the license  16  in a decrypted form), such items are also tightly bound. Signature validation also ensures that the digital content  12  and the license  16  are in the same form as issued from the content server  22  and the license server  24 , respectively. Accordingly, it is difficult if not impossible to decrypt the digital content  12  by bypassing the license server  24 , and also difficult if not impossible to alter and then decrypt the digital content  12  or the license  16 .  
     [0209] In one embodiment of the present invention, signature verification, and especially signature verification of the license  16 , is alternately performed as follows. Rather than having a signature encrypted by the private key of the license server  16  (PR-LS), as is seen in FIG. 8, each license  16  has a signature encrypted by a private root key (PR-R) (not shown), where the black box  30  of each DRM system  32  includes a public root key (PU-R) (also not shown) corresponding to the private root key (PR-R). The private root key (PR-R) is known only to a root entity, and a license server  24  can only issue licenses  16  if such license server  24  has arranged with the root entity to issue licenses  16 .  
     [0210] In particular, in such embodiment:  
     [0211] 1. the license server  24  provides its public key (PU-LS) to the root entity;  
     [0212] 2. the root entity returns the license server public key (PU-LS) to such license server  24  encrypted with the private root key (PR-R) (i.e., (CERT (PU-LS) S (PR-R))); and  
     [0213] 3. the license server  24  then issues a license  16  with a signature encrypted with the license server private key (S (PR-LS)), and also attaches to the license the certificate from the root entity (CERT (PU-LS) S (PR-R)).  
     [0214] For a DRM system  18  to validate such issued license  16 , then, the DRM system  18 :  
     [0215] 1. applies the public root key (PU-R) to the attached certificate (CERT (PU-LS) S (PR-R)) to obtain the license server public key (PU-LS); and  
     [0216] 2. applies the obtained license server public key (PU-LS) to the signature of the license  16  (S (PR-LS).  
     [0217] Importantly, it should be recognized that just as the root entity gave the license server  24  permission to issue licenses  16  by providing the certificate (CERT (PU-LS) S (PR-R)) to such license server  24 , such license server  24  can provide a similar certificate to a second license server  24  (i.e., (CERT (PU-LS2) S (PR-LS1)), thereby allowing the second license server to also issue licenses  16 . As should now be evident, a license  16  issued by the second license server would include a first certificate (CERT (PU-LS1) S (PR-R)) and a second certificate (CERT (PU-LS2) S (PR-LS1)). Likewise, such license  16  is validated by following the chain through the first and second certificates. Of course, additional links in the chain may be added and traversed.  
     [0218] One advantage of the aforementioned signature verification process is that the root entity may periodically change the private root key (PR-R), thereby likewise periodically requiring each license server  24  to obtain a new certificate (CERT (PU-LS) S (PR-R)). Importantly, as a requirement for obtaining such new certificate, each license server may be required to upgrade itself. As with the black box  30 , if a license server  24  is relatively current, i.e., has been upgraded relatively recently, it is less likely that license server  24  has been successfully attacked. Accordingly, as a matter of trust, each license server  24  is preferably required to be upgraded periodically via an appropriate upgrade trigger mechanism such as the signature verification process. Of course, other upgrade mechanisms may be employed without departing from the spirit and scope of the present invention.  
     [0219] Of course, if the private root key (PR-R) is changed, then the public root key (PU-R) in each DRM system  18  must also be changed. Such change may for example take place during a normal black box  30  upgrade, or in fact may require that a black box  30  upgrade take place. Although a changed public root key (PU-R) may potentially interfere with signature validation for an older license  16  issued based on an older private root key (PR-R), such interference may be minimized by requiring that an upgraded black box  30  remember all old public root keys (PU-R). Alternatively, such interference may be minimized by requiring signature verification for a license  16  only once, for example the first time such license  16  is evaluated by the license evaluator  36  of a DRM system  18 . In such case, state information on whether signature verification has taken place should be compiled, and such state information should be stored in the state store  40  of the DRM system  18 .  
     [0220] Digital Rights License  48   
     [0221] In the present invention, the license evaluator  36  evaluates a Digital Rights License (DRL)  48  as the rights description or terms of a license  16  to determine if such DRL  48  allows rendering of a corresponding piece of digital content  12  in the manner sought. In one embodiment of the present invention, the DRL  48  may be written by a licensor (i.e., the content owner) in any DRL language.  
     [0222] As should be understood, there are a multitude of ways to specify a DRL  48 . Accordingly, a high degree of flexibility must be allowed for in any DRL language. However, it is impractical to specify all aspects of a DRL  48  in a particular license language, and it is highly unlikely that the author of such a language can appreciate all possible licensing aspects that a particular digital licensor may desire. Moreover, a highly sophisticated license language may be unnecessary and even a hindrance for a licensor providing a relatively simple DRL  48 . Nevertheless, a licensor should not be unnecessarily restricted in how to specify a DRL  48 . At the same time, the license evaluator  36  should always be able to get answers from a DRL  48  regarding a number of specific license questions.  
     [0223] In the present invention, and referring now to FIG. 11, a DRL  48  can be specified in any license language, but includes a language identifier or tag  54 . The license evaluator  36  evaluating the license  16 , then, performs the preliminary step of reviewing the language tag  54  to identify such language, and then selects an appropriate license language engine  52  for accessing the license  16  in such identified language. As should be understood, such license language engine  52  must be present and accessible to the license evaluator  36 . If not present, the language tag  54  and/or the DRL  48  preferably includes a location  56  (typically a web site) for obtaining such language engine  52 .  
     [0224] Typically, the language engine  52  is in the form of an executable file or set of files that reside in a memory of the user&#39;s computing device  14 , such as a hard drive. The language engine  52  assists the license evaluator  36  to directly interrogate the DRL  48 , the license evaluator  36  interrogates the DRL  48  indirectly via the language engine  48  acting as an intermediary, or the like. When executed, the language engine  52  runs in a work space in a memory of the user&#39;s computing device  14 , such as RAM. However, any other form of language engine  52  may be employed without departing from the spirit and scope of the present invention.  
     [0225] Preferably, any language engine  52  and any DRL language supports at least a number of specific license questions that the license evaluator  36  expects to be answered by any DRL  48 , as will be discussed below. Accordingly, the license evaluator  36  is not tied to any particular DRL language; a DRL  48  may be written in any appropriate DRL language; and a DRL  48  specified in a new license language can be employed by an existing license evaluator  36  by having such license evaluator  36  obtain a corresponding new language engine  52 .  
     [0226] DRL Languages  
     [0227] Two examples of DRL languages, as embodied in respective DRLs  48 , are provided below. The first, ‘simple’ DRL  48  is written in a DRL language that specifies license attributes, while the second ‘script’ DRL  48  is written in a DRL language that can perform functions according to the script specified in the DRL  48 . While written in a DRL language, the meaning of each line of code should be apparent based on the linguistics thereof and/or on the attribute description chart that follows:  
                                  Simple DRL 48:                         &lt;LICENSE&gt;           &lt;DATA&gt;           &lt;NAME&gt;Beastie Boy&#39;s Play&lt;/NAME&gt;           &lt;ID&gt;39384&lt;/ID&gt;           &lt;DESCRIPTION&gt;Play the song 3 times&lt;/DESCRIPTION&gt;           &lt;TERMS&gt;&lt;/TERMS&gt;           &lt;VALIDITY&gt;           &lt;NOTBEFORE&gt;19980102 23:20:14Z&lt;/NOTBEFORE&gt;           &lt;NOTAFTER&gt;19980102 23:20:14Z&lt;/NOTAFTER&gt;           &lt;/VALIDITY&gt;           &lt;ISSUEDDATE&gt;19980102 23:20:14Z&lt;/ISSUEDDATE&gt;           &lt;LICENSORSITE&gt;http://www.foo.com&lt;/LICENSORSITE&gt;           &lt;CONTENT&gt;           &lt;NAME&gt;Beastie Boy&#39;s&lt;/NAME&gt;           &lt;ID&gt;392&lt;/ID&gt;           &lt;KEYID&gt;39292&lt;/KEYID&gt;           &lt;TYPE&gt;MS Encrypted ASF 2.0&lt;/TTYPE&gt;           &lt;/CONTENT&gt;           &lt;OWNER&gt;           &lt;ID&gt;939KDKD393KD&lt;/ID&gt;           &lt;NAME&gt;Universal&lt;/NAME&gt;           &lt;PUBLICKEY&gt;&lt;/PUBLICKEY&gt;           &lt;/OWNER&gt;           &lt;LICENSEE&gt;           &lt;NAME&gt;Arnold&lt;/NAME&gt;           &lt;ID&gt;939KDKD393KD&lt;/ID&gt;           &lt;PUBLICKEY&gt;&lt;/PUBLICKEY&gt;           &lt;/LICENSEE&gt;           &lt;PRINCIPAL TYPE==AND=&gt;           &lt;PRINCIPAL TYPE==OR=&gt;           &lt;PRINCIPAL&gt;           &lt;TYPE&gt;×86Computer&lt;/TYPE&gt;           &lt;ID&gt;3939292939d9e939&lt;/ID&gt;           &lt;NAME&gt;Personal Computer&lt;/NAME&gt;           &lt;AUTHTYPE&gt;Intel Authenticated Boot PC SHA-1                 DSA512&lt;/AUTHTYPE&gt;                         &lt;AUTHDATA&gt;29293939&lt;/AUTHDATA&gt;           &lt;/PRINCIPAL&gt;           &lt;PRINCIPAL&gt;           &lt;TYPE&gt;Application&lt;/TYPE&gt;           &lt;ID&gt;2939495939292&lt;/ID&gt;           &lt;NAME&gt;Window=s Media Player&lt;/NAME&gt;           &lt;AUTHTYPE&gt;Authenticode SHA-1&lt;/AUTHTYPE&gt;           &lt;AUTHDATA&gt;93939&lt;/AUTHDATA&gt;           &lt;/PRINCIPAL&gt;           &lt;/PRINCIPAL&gt;           &lt;PRINCIPAL&gt;           &lt;TYPE&gt;Person&lt;/TYPE&gt;           &lt;ID&gt;39299482010&lt;/ID&gt;           &lt;NAME&gt;Arnold Blinn&lt;/NAME&gt;           &lt;AUTHTYPE&gt;Authenticate user&lt;/AUTHTYPE&gt;           &lt;AUTHDATA&gt;\\redmond\arnoldb&lt;/AUTHDATA&gt;           &lt;/PRINCIPAL&gt;           &lt;/PRINCIPAL&gt;           &lt;DRLTYPE&gt;Simple&lt;/DRLTYPE&gt; [the language tag 54]           &lt;DRLDATA&gt;           &lt;START&gt;19980102 23:20:14Z&lt;/START&gt;           &lt;END&gt;19980102 23:20:14Z&lt;/END&gt;           &lt;COUNT&gt;3&lt;/COUNT&gt;           &lt;ACTION&gt;PLAY&lt;/ACTION&gt;           &lt;/DRLDATA&gt;           &lt;ENABLINGBITS&gt;aaaabbbbccccdddd&lt;/ENABLINGBITS&gt;           &lt;/DATA&gt;           &lt;SIGNATURE&gt;           &lt;SIGNERNAME&gt;Universal&lt;/SIGNERNAME&gt;           &lt;SIGNERID&gt;9382ABK3939DKD&lt;/SIGNERID&gt;           &lt;HASHALGORITHMID&gt;MD5&lt;/HASHALGORITHMID&gt;           &lt;SIGNALGORITHMID&gt;RSA 128&lt;/SIGNALGORITHMID&gt;           &lt;SIGNATURE&gt;xxxyyyxxxyyyxxxyyy&lt;/SIGNATURE&gt;           &lt;SIGNERPUBLICKEY&gt;&lt;/SIGNERPUBLICKEY&gt;           &lt;CONTENTSIGNEDSIGNERPUBLICKEY&gt;&lt;/CONTENTSIGNEDSI                 GNERPUBLICKEY&gt;                         &lt;/SIGNATURE&gt;           &lt;/LICENSE&gt;                 Script DRL 48:                         &lt;LICENSE&gt;           &lt;DATA&gt;           &lt;NAME&gt;Beastie Boy&#39;s Play&lt;/NAME&gt;           &lt;ID&gt;39384&lt;/ID&gt;           &lt;DESCRIPTION&gt;Play the song unlimited&lt;/DESCRIPTION&gt;           &lt;TERMS&gt;&lt;/TERMS&gt;           &lt;VALIDITY&gt;           &lt;NOTBEFORE&gt;19980102 23:20:14Z&lt;/NOTBEFORE&gt;           &lt;NOTAFTER&gt;19980102 23:20:14Z&lt;/NOTAFTER&gt;           &lt;/VALIDITY&gt;           &lt;ISSUEDDATE&gt;19980102 23:20:14Z&lt;/ISSUEDDATE&gt;           &lt;LICENSORSITE&gt;http://www.foo.com&lt;/LICENSORSITE&gt;           &lt;CONTENT&gt;           &lt;NAME&gt;Beastie Boy&#39;s&lt;/NAME           &lt;ID&gt;392&lt;/ID&gt;           &lt;KEYID&gt;39292&lt;/KEYID&gt;           &lt;TYPE&gt;MS Encrypted ASF 2.0&lt;/TTYPE&gt;           &lt;/CONTENT&gt;           &lt;OWNER&gt;           &lt;ID&gt;939KDKD393KD&lt;/ID&gt;           &lt;NAME&gt;Universal&lt;/NAME&gt;           &lt;PUBLICKEY&gt;&lt;/PUBLICKEY&gt;           &lt;/OWNER&gt;           &lt;LICENSEE&gt;           &lt;NAME&gt;Arnold&lt;/NAME&gt;           &lt;ID&gt;939KDKD393KD&lt;/ID&gt;           &lt;PUBLICKEY&gt;&lt;/PUBLICKEY&gt;           &lt;/LICENSEE&gt;           &lt;DRLTYPE&gt;Script&lt;/DRLTYPE&gt; [the language tag 54]           &lt;DRLDATA&gt;           function on_enable(action, args) as boolean           result = False           if action = “PLAY” then           result = True           end if           on_action = False           end function           . . .            &lt;/DRLDATA&gt;           &lt;/DATA&gt;           &lt;SIGNATURE&gt;           &lt;SIGNERNAME&gt;Universal&lt;/SIGNERNAME&gt;           &lt;SIGNERID&gt;9382&lt;/SIGNERID&gt;           &lt;SIGNERPUBLICKEY&gt;&lt;/SIGNERPUBLICKEY&gt;           &lt;HASHID&gt;MD5&lt;/HASHID&gt;           &lt;SIGNID&gt;RSA 128&lt;/SIGNID&gt;           &lt;SIGNATURE&gt;xxxyyyxxxyyyxxxyyy&lt;/SIGNATURE&gt;           &lt;CONTENTSIGNEDSIGNERPUBLICKEY&gt;&lt;/CONTENTSIGNEDSI                 GNERPUBLICKEY&gt;                         &lt;/SIGNATURE&gt;           &lt;/LICENSE&gt;                      
 
     [0228] In the two DRLs  48  specified above, the attributes listed have the following descriptions and data types:  
                                       Attribute   Description   Data Type                  Id   ID of the license   GUID       Name   Name of the license   String       Content Id   ID of the content   GUID       Content Key Id   ID for the encryption key of the   GUID           content       Content Name   Name of the content   String       Content Type   Type of the content   String       Owner Id   ID of the owner of the content   GUID       Owner Name   Name of the owner of the content   String       Owner Public Key   Public key for owner of content   String           This is a base-64 encoded public           key for the owner of the content.       Licensee Id   Id of the person getting license. It   GUID           may be null.       Licensee Name   Name of the person getting license.   String           It may be null.       Licensee Public Key   Public key of the licensee. This is   String           the base-64 encoded public key of           the licensee. It may be null.       Description   Simple human readable description   String           of the license       Terms   Legal terms of the license. This   String           may be a pointer to a web page           containing legal prose.       Validity Not After   Validity period of license expiration   Date       Validity Not Before   Validity period of license start   Date       Issued Date   Date the license was issued   Date       DRL Type   Type of the DRL. Example include   String           “SIMPLE” or “SCRIPT”       DRL Data   Data specific to the DRL   String       Enabling Bits   These are the bits that enable   String           access to the actual content. The           interpretation of these bits is up to           the application, but typically this will           be the private key for decryption of           the content. This data will be base-           64 encoded. Note that these bits           are encrypted using the public key           of the individual machine.       Signer Id   ID of person signing license   GUID       Signer Name   Name of person signing license   String       Signer Public Key   Public key for person signing   String           license. This is the base-64 encode           public key for the signer.       Content Signed Signer   Public key for person signing the   String       Public Key   license that has been signed by the           content server private key. The           public key to verify this signature           will be encrypted in the content.           This is base-64 encoded.       Hash Alg Id   Algorithm used to generate hash.   String           This is a string, such as “MD5”.       Signature Alg Id   Algorithm used to generate   String           signature. This is a string, such as           “RSA 128”.       Signature   Signature of the data. This is base-   String           64 encoded data.                  
 
     [0229] Methods  
     [0230] As was discussed above, it is preferable that any language engine  52  and any DRL language support at least a number of specific license questions that the digital license evaluator  36  expects to be answered by any DRL  48 . Recognizing such supported questions may include any questions without departing from the spirit and scope of the present invention, and consistent with the terminology employed in the two DRL  48  examples above, in one embodiment of the present invention, such supported questions or ‘methods’ include ‘access methods’, ‘DRL methods’, and ‘enabling use methods’, as follows:  
     [0231] Access Methods  
     [0232] Access methods are used to query a DRL  48  for top-level attributes.  
     [0233] VARIANT QueryAttribute (BSTR key)  
     [0234] Valid keys include License.Name, License.Id, Content.Name, Content.Id, Content.Type, Owner.Name, Owner.Id, Owner.PublicKey, Licensee.Name, Licensee.Id, Licensee.PublicKey, Description, and Terms, each returning a BSTR variant; and Issued, Validity.Start and Validity.End, each returning a Date Variant.  
     [0235] DRL Methods  
     [0236] The implementation of the following DRL methods varies from DRL  48  to DRL  48 . Many of the DRL methods contain a variant parameter labeled ‘data’ which is intended for communicating more advanced information with a DRL  48 . It is present largely for future expandability.  
     [0237] Boolean IsActivated(Variant data)  
     [0238] This method returns a Boolean indicating whether the DRL  48 /license  16  is activated. An example of an activated license  16  is a limited operation license  16  that upon first play is active for only 48 hours.  
     [0239] Activate(Variant data)  
     [0240] This method is used to activate a license  16 . Once a license  16  is activated, it cannot be deactivated.  
     [0241] Variant QueryDRL(Variant data)  
     [0242] This method is used to communicate with a more advanced DRL  48 . It is largely about future expandability of the DRL  48  feature set.  
     [0243] Variant GetExpires(BSTR action, Variant data)  
     [0244] This method returns the expiration date of a license  16  with regard to the passed-in action. If the return value is NULL, the license  16  is assumed to never expire or does not yet have an expiration date because it hasn&#39;t been activated, or the like.  
     [0245] Variant GetCount(BSTR action, Variant data)  
     [0246] This method returns the number of operations of the passed-in action that are left. If NULL is returned, the operation can be performed an unlimited number of times.  
     [0247] Boolean IsEnabled(BSTR action, Variant data)  
     [0248] This method indicates whether the license  16  supports the requested action at the present time.  
     [0249] Boolean IsSunk(BSTR action, Variant data)  
     [0250] This method indicates whether the license  16  has been paid for. A license  16  that is paid for up front would return TRUE, while a license  16  that is not paid for up front, such as a license  16  that collects payments as it is used, would return FALSE.  
     [0251] Enabling Use Methods  
     [0252] These methods are employed to enable a license  16  for use in decrypting content.  
     [0253] Boolean Validate (BSTR key)  
     [0254] This method is used to validate a license  16 . The passed-in key is the black box  30  public key (PU-BB) encrypted by the decryption key (KD) for the corresponding digital content  12  (i.e.,(KD(PU-BB))) for use in validation of the signature of the license  16 . A return value of TRUE indicates that the license  16  is valid. A return value of FALSE indicates invalid.  
     [0255] int OpenLicense  16 (BSTR action, BSTR key, Variant data)  
     [0256] This method is used to get ready to access the decrypted enabling bits. The passed-in key is (KD(PU-BB)) as described above. A return value of  0  indicates success. Other return values can be defined.  
     [0257] BSTR GetDecryptedEnablingBits (BSTR action, Variant data) Variant GetDecryptedEnablingBitsAsBinary (BSTR action, Variant Data)  
     [0258] These methods are used to access the enabling bits in decrypted form. If this is not successful for any of a number of reasons, a null string or null variant is returned.  
     [0259] void CloseLicense (BSTR action, Variant data)  
     [0260] This method is used to unlock access to the enabling bits for performing the passed-in action. If this is not successful for any of a number of reasons, a null string is returned.  
     [0261] Heuristics  
     [0262] As was discussed above, if multiple licenses  16  are present for the same piece of digital content  12 , one of the licenses  16  must be chosen for further use. Using the above methods, the following heuristics could be implemented to make such choice. In particular, to perform an action (say APLAY@) on a piece of digital content  12 , the following steps could be performed:  
     [0263] 1. Get all licenses  16  that apply to the particular piece of digital content  12 .  
     [0264] 2. Eliminate each license  16  that does not enable the action by calling the IsEnabled function on such license  16 .  
     [0265] 3. Eliminate each license  16  that is not active by calling IsActivated on such license  16 .  
     [0266] 4. Eliminate each license  16  that is not paid for up front by calling IsSunk on such license  16 .  
     [0267] 5. If any license  16  is left, use it. Use an unlimited-number-of-plays license  16  before using a limited-number-of-plays license  16 , especially if the unlimited-number-of-plays license  16  has an expiration date. At any time, the user should be allowed to select a specific license  16  that has already been acquired, even if the choice is not cost-effective. Accordingly, the user can select a license  16  based on criteria that are perhaps not apparent to the DRM system  32 .  
     [0268] 6. If there are no licenses  16  left, return status so indicating.  
     [0269] The user would then be given the option of:  
     [0270] using a license  16  that is not paid for up front, if available;  
     [0271] activating a license  16 , if available; and/or  
     [0272] performing license acquisition from a license server  24 .  
     [0273] Content Protection Techniques—Video Card  
     [0274] In the DRM architecture  10  of the present invention, rights-protected content  12  is delivered in an encrypted form and is to be decrypted only in accordance with rights specified in a corresponding license  16 . As may be appreciated, many precautions are taken to ensure that the content  10  in the decrypted form is not obtainable, unless of course allowable according to the license  16 . Thus, for example, path authentication may be employed to ensure that each module receiving decrypted content  12  can be trusted to act responsibly and not provide such decrypted content  12  to an unscrupulous entity such as a ‘content thief’. Such path authentication is described more fully in U.S. patent application Ser. No. 09/525,510, filed Mar. 15, 2000, entitled “RELEASING DECRYPTED DIGITAL CONTENT TO AN AUTHENTICATED PATH”, and hereby incorporated by reference in its entirety.  
     [0275] However, it is to be appreciated that decrypted content  12  or at least a portion thereof is necessarily stored in buffers and other memory devices in the normal course of rendering such decrypted content  12 . More specifically, the decrypted content  12  in such buffer is obtainable without excessive effort by a content thief.  
     [0276] Especially in the case of content  12  such as video content, and as seen in FIG. 13, such content  12  upon being decrypted is ultimately stored in a video card  60 . In particular, and as may be appreciated, video data, after being decrypted ion and/or decompressed, is written to video RAM (VRAM)  62  on the video card  60  prior to being employed by the video card  60  to produce a video signal to be sent to a monitor  64  or the like. Operation of video cards is known or should be apparent to the relevant public and therefore need not be discussed herein in any detail. Importantly, while on the VRAM  62  at the video card  60 , the video data is susceptible to theft by a content thief employing hardware and/or software to read such video data from such VRAM  62 . Such VRAM  62 , then, is a vehicle for a content thief to steal good quality video data regardless of the capabilities of the core DRM system  32 .  
     [0277] Content Protection Techniques—Video Card—Write-Only VRAM  
     [0278] Accordingly, in one embodiment of the present invention, the VRAM  62  on the video card  60  is configured to be write-only except with regard to the video card  60  itself. Thus, any entity external to the video card  60 , such as a content thief, cannot read such video data on the VRAM  62 . Such configuration may apply only with regard to the DRM system  32  and protected content  12  controlled thereby, or may be with regard to all content be it protected or unprotected.  
     [0279] In the former case, the protected content  12  may be accompanied by an appropriate signal to the video card  60  and VRAM  62  to implement write-only functionality. Such a signal may be a hardware or software signal from the DRM system  32  or the rendering application  34 , for example, and is known or should be apparent to the relevant public and therefore need not be described herein in any detail. Accordingly, any appropriate signal may be employed without departing from the spirit and scope of the present invention. In the latter case, a resultant by-product is that no person or program can read from the VRAM  62  on the video card at all, even if such person or program has nothing but good intentions.  
     [0280] In one embodiment of the present invention, write-only VRAM  62  is implemented in a video card  60  by creating one or more write-only buffers hosted in the VRAM  62 . In the simplest case, each write-only buffer can be a bitmapped secondary video surfaces that is displayed over the primary surface. Importantly, bitmap data can be written to each buffer, but reading the data returns black, color-key, nonsense, noise, or the like.  
     [0281] To be write-only, the video card  60  of the present invention must not provide any other way of reading the pixels that comprise the protected screen area. For example, there must be no separate Read Pixel operation that provides access to protected screen areas. Alternatively, existing mechanisms employed to read pixels should return black, color-key, nonsense, noise or the like.  
     [0282] In addition, write-only VRAM  62  is implemented in a video card  60  by imparting the video card  60  with the functionality necessary to clear or zero the contents of each write-only buffer when freed. Thus, such write-only buffer cannot be read by an attacking process after being freed but before being over-written.  
     [0283] The present scheme is equally applicable to other video processing architectures without departing from the spirit and scope of the present invention. For example, if the video card  60  supports decompression acceleration, similar rules apply. In particular, each buffer that communicates with the video accelerator on such video card  60  is write-only, and the video rendered thereto is not readable by other means.  
     [0284] Content Protection Techniques—Video Card—Authentication  
     [0285] Of course, the DRM system  32  must be able to satisfy itself that the video card  60  and VRAM  62  thereon are trustworthy in that such VRAM  62  on such video card  60  is write-only in accordance with the present invention. Thus, the video card  60  must be able to authenticate itself to such DRM system  32  as having the write-only VRAM  62 .  
     [0286] Presumably, the DRM system  32  can provide good assurance that a VRAM  62 /video buffer is indeed write-only through occasional read-back-checks, and other standard anti-debugging technology. However, such checks do not negate the possibility that the protected video data is available by some other mechanism such as for example double-mapped memory, a bit-transfer to unprotected memory, a Read Pixel command, or the like.  
     [0287] One difficulty encountered in connection with authentication is that a video card manufacturer does not necessarily wish to implement such authentication. In particular, if video data is in fact available to a content thief or the like by way of a manufacturer&#39;s video card, such card is more attractive and marketable. Conceivably, then, a legitimate and upstanding video card manufacturer that abides by the scheme of the present invention and therefore implements content protection can lose market share and position a less-than-legitimate and non-compliant video card manufacturer. Accordingly, authentication must be achieved despite such difficulties.  
     [0288] Following are several mechanisms for allowing such authentication:  
     [0289] Legal Devices  
     [0290] In one embodiment of the present invention, the video card  60  authenticates itself to the DRM system  32  in a generally passive manner by having one or more elements  65  that are legally protected through one or more intellectual property rights (patents, copyrights, trademarks, trade secrets, etc.), where each element  65  must be incorporated in the video card  60 . Thus, a manufacture who wishes to manufacture the video card  60  with the rights-protected element  65  must obtain a license to do so and must among other things agree to obey certain predetermined license-type rules in the course of manufacturing the video card  60  with the rights-protected element  65 , the most important of which being that the VRAM  62  thereon is to be write-only in the manner discussed above. As may be appreciated, in such embodiment, the DRM system  32  has no way of positively determining that an associated video card  60  is compliant.  
     [0291] In a similar embodiment of the present invention, the video card  60  authenticates itself to the DRM system  32  in a more active manner by having incorporated therein one or more of the aforementioned elements  65  protected by one or more of the aforementioned intellectual property rights (patents, copyrights, trademarks, trade secrets, etc.), but where the element  65  is in a form that may be presented upon request or that may present upon request an appropriate token  67  to the DRM system  32 , rendering application  34 , and/or other entity on the computing system  14 .  
     [0292] Thus, the protected subject matter may be hardware or software that presents a digital signal, or a software construct that is itself to be presented. A manufacture who wishes to manufacture the video card with the element  65  must obtain a license to do so and must among other things agree to obey certain predetermined license-type rules in the course of manufacturing the video card  60  with the element  65 , the most important of which being that the VRAM  62  thereon is to be write-only in the manner discussed above. In return, the manufacture receives the element  65  for incorporation into the video card  60 , or is authorized to incorporate such element  65  into the video card  60 . A non-licensing manufacturer may also incorporate the element  65  into its video card  60 , but doing so would expose the non-licensing manufacturer to prosecution for infringement of intellectual property rights related to the element  65 .  
     [0293] Technical Devices  
     [0294] In one embodiment of the present invention, the video card  60  authenticates itself to the DRM system  32  in a generally active manner by way of a cryptographic authentication scheme. Here, the video card  60  bears a cryptographic certificate such as a digital certificate  66  or the like that can be presented to the DRM system  32 , rendering application  34 , or other requesting entity to certify that the video card  60  can be trusted. The digital certificate  66  as presented may then be reviewed on the computing device  14  against a regularly or irregularly updated list  68  of acceptable and/or unacceptable certificates  66  or the like, and the decision on whether to trust the video card  60  may be based thereon, at least in part. Note that in such embodiment, the video card  60  must be provided with the functionality to both retain the certificate  66  in a non-volatile manner and present the certificate  66  to an appropriate requesting entity upon demand.  
     [0295] Preferably, an appropriate certificate  66  is provided to the manufacturer of the video card  60  upon the manufacturer agreeing to obey certain predetermined license-type rules in the course of manufacturing the video card  60 , the most important of which being that the VRAM  62  thereon is to be write-only in the manner discussed above. Such provided certificate  66  is then appropriately incorporated into the video card  60  during the manufacture thereof by the manufacturer. If the manufacturer reneges on the agreement by for example manufacturing the video card  60  with readable VRAM  62 , the certificate  66  may be placed on the aforementioned unacceptable list  68 . Incorporating and providing the certificate  66  and providing the list  68  to a computing device  14  and updating such list  68  on the computing device  14  are known or should be apparent to the relevant public and therefore need not be discussed herein in any detail. Thus, any method of incorporating and providing the certificate  66  and providing and updating the list  68  may be employed without departing from the spirit and scope of the present invention.  
     [0296] Note that in using a digital certificate  66 , a video card requires a small cryptographic processor, or else cryptographic code running on the processor of the computing device  14 , and a unique certified key  70 . The DRM system  32 , rendering application  34 , or other entity on the computing device  14  may perform an authentication such as a cryptographic challenge/response on the video card  60  to see if the card-signing key  70  is appropriately certified as being on the acceptable list  68  and/or not on the unacceptable list  68 .  
     [0297] Note that the use of a certificate  66  and key  70  does not allow a non-licensed manufacturer to impersonate a licensed manufacturer. Also, if a certificate  66  is compromised, the list  68  may be updated to mark the compromised certificate  66  as unacceptable.  
     [0298] Authentication in Use  
     [0299] In the simplest embodiment, at least a portion of VRAM  62  on a video card  60  is permanently write-only and cannot be configured otherwise. In this case, it is enough for the video card  60  to confirm to the computing device  14  its type (i.e. a trusted video card with permanent write-only VRAM at address range X) during authentication. Thereafter, the authenticating entity on the computing device  14  knows that data can be written to address range X and that such written data will only be readable by the trusted video card  60 .  
     [0300] However, authenticating the video card  60  in itself is not enough if the video card can be configured from among several modes (write-only vs. read-write, e.g.). If the configuration can be set by an un-trusted entity, an attacker could wait until the writer of the original data has authenticated and configured a write-only buffer on the video card, reconfigure the buffer to be read-write, and then read the data as it written to the VRAM  62 . This problem is especially relevant in the context of modern multi-tasking operating systems, which allow arbitrary collections of processes to run side-by-side on the same computing device  14 . The problem can be addressed in a plurality of ways:  
     [0301] 1. Authenticated state checking: The video card  60  can be reconfigured without restriction. However, such card  60  allows processes on the host computing device  14  to query its configuration/state in an authenticated way. That is, just like the initial authentication allows the video card  60  to confirm to the host device  14  that it is a trusted video card of type XYZ and that a write-only buffer has been allocated at address range ABC, additional authentication(s) allow the video card  60  to confirm that the configuration has been unchanged for the past Y minutes, or the like.  
     [0302] 2. Authenticated configuration changes: This requires the video card  60  to authenticate the entity that is requesting the configuration change. In principle, this authentication can be completely independent from the authentication of the video card  60  by the computing device  14 . Here, the initial request for a write-only buffer from the device  14  may describe a policy on who is allowed to reconfigure the buffer and in which ways. The policy may for example take the form of a license  16 , or the like.  
     [0303] In authenticating the video card  60 , a process on the host computing device  14  may call functions such as:  
     [0304] GetWriteOnlyBuffer(int buffersize); and  
     [0305] ReconfigureBuffer(configuration description),  
     [0306] and public key-private key encryption may be employed whereby the video card  60  has a private key and the corresponding public key is placed in a certificate from a trusted entity. Thus, the certificate with public key is made available to a content source (CS) on the host device  14 , and CS checks the validity of the certificate, for example by verifying the digital signature and/or testing for expiry dates or revocation.  
     [0307] CS as part of an initial configuration of the VRAM  62  (i.e., in conjunction with the of the GetWriteOnlyBuffer function above) then generates a random number Z (a nonce) and encrypts Z with the public key from the certificate to result in PU (Z), and then sends PU (Z) to the video card  60 . The video card uses the private key to decrypt PU (Z), thus resulting in Z, and then sends a message (Z, M, S) to CS, where M is an arbitrary message text and S is a digital signature over X,M made with the private key. In the present example, the text of M could be to the effect that “The memory range between addresses a and b has been configured as write-only”. Presumably, the video card  60  is in fact so configured.  
     [0308] Authentication of a re-configuration (i.e., in conjunction with the ReconfigureBuffer function above), then, is based on the knowledge of Z. That is, a caller requesting that the video card  60  re-configure the VRAM  62  has to demonstrate knowledge of Z, or else the video card  60  refuses the request. Presumably, only CS knows Z, and therefore an attacker without knowledge of Z fails.  
     [0309] Such authentication may for example comprise CS sending a message (M, m) to the video card  60 , where M is a message to the effect of “please configure the buffer a . . . b as follows . . . ” and m is the result of computing the message authentication code m=MAC(M, Z). Accordingly, the video card  60  uses its own copy of Z to verify the MAC. In particular, the video card  60  honors the re-configuration request only if the MAC verifies.  
     [0310] In addition to using write-only VRAM  62  or as an alternative, CS may encrypt the video data such that it can only be decrypted by the video card  60 . As in the case of write-only VRAM  62 , this requires an authentication which allows CS to verify that the data is encrypted for a trustworthy video card  60 . Typically, the authentication mechanism will allow CS and the video card to establish a shared secret (session key) Z. Thus, in order to send data to the video card  60 , CS encrypts the data according to Z and the video card decrypts the data according to Z.  
     [0311] Conclusion  
     [0312] The programming necessary to effectuate the processes performed in connection with the present invention is relatively straight-forward and should be apparent to the relevant programming public. Accordingly, such programming is not attached hereto. Any particular programming, then, may be employed to effectuate the present invention without departing from the spirit and scope thereof.  
     [0313] In the foregoing description, it can be seen that the present invention comprises a new and useful enforcement architecture  10  that allows the controlled rendering or playing of arbitrary forms of digital content  12 , where such control is flexible and definable by the content owner of such digital content  12 . Also, the present invention comprises a new useful controlled rendering environment that renders digital content  12  only as specified by the content owner, even though the digital content  12  is to be rendered on a computing device  14  which is not under the control of the content owner. Further, the present invention comprises a secure video card  60  on the computing device  14  to prevent a content thief from stealing content residing on the video card  60 .  
     [0314] It should be appreciated that changes could be made to the embodiments described above without departing from the inventive concepts thereof. Principally, it is to be understood that the present invention need not be restricted merely to a video card  60 . Instead, the present invention is intended to encompass any type of device having memory that is to store decrypted data, such as for example a sound card. Likewise, it is to be understood that the present invention is not restricted to a DRM system such as the DRM system  32  disclosed above in connection with FIGS.  1 - 11 . Instead, the present invention is intended to encompass any type of DRM system including any system that maintains a secure environment or provides a security module for protecting data from unauthorized use and/or access.  
     [0315] Central to the present invention is that the memory is read-only except to the device, and that the device can authenticate itself as being trustworthy. These concepts apply to any kind of content  12  and device as long as the content flow is unidirectional (i.e., one-way: CPU/main memory to device having memory to other device (e.g. monitor, speakers, etc.)). It should be understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.