Patent Publication Number: US-7716745-B2

Title: Binding a digital license to a portable device or the like in a digital rights management (DRM) system and checking out/checking in the digital license to/from the portable device or the like

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a continuation of U.S. patent application Ser. No. 11/432,276, filed on May 10, 2006, which is a divisional of U.S. patent application Ser. No. 09/892,371, filed Jun. 27, 2001, which in turn is related to U.S. patent application Ser. No. 09/645,887, filed Aug. 25, 2000 and entitled “BINDING DIGITAL CONTENT TO A PORTABLE STORAGE DEVICE OR THE LIKE IN A DIGITAL RIGHTS MANAGEMENT (DRM) SYSTEM”, 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”, all of which are hereby incorporated by reference in their entireties. 

   TECHNICAL FIELD 
   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. 
   BACKGROUND OF THE INVENTION 
   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. 
   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 redistributing such content to a second user, at least in a manner that denies the content owner a license fee from such second user. 
   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. 
   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. 
   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 redistribute 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. 
   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. 
   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. As but one example, such a trusted software component prevents a user of the computing device from making a copy of such digital content, except as otherwise allowed for by the content owner thereof. 
   SUMMARY OF THE INVENTION 
   In the present invention, a method is provided for rendering encrypted digital content on a first device having a public key (PU 1 ) and a corresponding private key (PR 1 ), where the digital content being encrypted according to a content key (KD). In the method, a digital license corresponding to the content is obtained, where the digital license including the content key (KD) therein in an encrypted form. The encrypted content key (KD) from the digital license is decrypted to produce the content key (KD), and the public key (PU 1 ) of the first device is obtained therefrom. The content key (KD) is then encrypted according to the public key (PU 1 ) of the first device (PU 1  (KD)), and a sub-license corresponding to and based on the obtained license is composed, where the sub-license includes (PU 1  (KD)). The composed sub-license is then transferred to the first device, wherein the first device can decrypt (PU 1  (KD)) with the private key thereof (PR 1 ) to produce the content key (KD), and can render the encrypted content on the first device with the produced content key (KD). 
   To check out a sub-license from a second device to a first device, the second device requests a nonce from the first device, and receives such nonce. The second device then sends the checked-out sub-license and the received nonce to the first device. The first device then concludes that the nonce sent by the second device is the same nonce received by the second device, and therefore that the sent sub-license that accompanies the sent nonce is legitimate, and stores the sent sub-license. To check in the checked-out sub-license, the first device deletes the checked-out sub-license and then provides a trusted indication to the second device that the checked-out sub-license has in fact been deleted. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
       FIG. 1  is a block diagram showing an enforcement architecture in accordance with one embodiment of the present invention; 
       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; 
       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; 
       FIG. 4  is a block diagram of the users computing device of  FIG. 1  in accordance with one embodiment of the present invention; 
       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; 
       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; 
       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; 
       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; 
       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; 
       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; 
       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; 
       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; 
       FIG. 13  is a block diagram representing an arrangement wherein a portable device couples to a computer for purposes of downloading content and a corresponding sub-license in accordance with one embodiment of the present invention; 
       FIGS. 14 and 14A  are flow diagrams showing steps performed in delivering digital content and a sub-license from the computer to the portable device of  FIG. 13  in accordance with one embodiment of the present invention; 
       FIG. 15  is a block diagram showing a license and a sub-license derived from the license in the manner shown in  FIG. 14  in accordance with one embodiment of the present invention; 
       FIG. 16  is a flow diagram showing steps performed by the portable device of  FIG. 13  in rendering content based on a sub-license in accordance with one embodiment of the present invention; and 
       FIG. 17  is a flow diagram showing steps performed by the computer and the portable device of  FIG. 13  to check out and check in a sub-license in accordance with one embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   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 . 
   Computer Environment 
     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. 
   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 . 
   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  120 . 
   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. 
   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 . 
   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. 
   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. 
   Architecture 
   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 users computing device  14 . 
   Architecture—Authoring Tool  18   
   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 . 
   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. 
   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. 
   In use, the authoring tool  18  is supplied with information including, among other things:
         the digital content  12  to be packaged;   the type and parameters of watermarking and/or fingerprinting to be employed, if any;   the type and parameters of data compression to be employed, if any;   the type and parameters of encryption to be employed;   the type and parameters of serialization to be employed, if any; and   the instructions and/or rules that are to accompany the digital content  12 .       

   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 . 
   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. 
   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 . 
   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. 
   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:
         the name of the input file  29   a  having the digital content  12 ;   the type of encoding that is to take place   the encryption/decryption key (KD) to be employed,   the accompanying instructions/rules/information (‘header information’) to be packaged with the digital content  12  in the package  12   p.      the type of muxing that is to occur; and   the name of the output file  29   b  to which the package  12   p  based on the digital content  12  is to be written.       

   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. 
   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. 
   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.    
   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.    
   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. 
   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. 
   Architecture—Content Server  22   
   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. 
   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. 
   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. 
   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. 
   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. 
   Structure of Digital Content Package  12   p    
   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:
         the digital content  12  encrypted with the encryption/decryption key (KD), as was discussed above (i.e., (KD(CONTENT)));   the content ID (or package ID) of such digital content  12  (or package  12   p );   the key ID of the decryption key (KD);   license acquisition information, preferably in an un-encrypted form; and   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))).       

   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)). 
   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 (KC) (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:
         the content server  22  sending (PU-CS) to the authoring tool  18 ;   the authoring tool  18  encrypting (PU-CS) with (KD) to produce (KD (PU-CS));   the authoring tool  18  sending (KD (PU-CS)) to the content server  22 ;   the content server  22  signing (KD (PU-CS)) with (PR-CS) to produce (KD (PU-CS) S (PR-CS)); and   the content server  22  sending (KD (PU-CS) S (PR-CS)) to the authoring tool  18 .
 
Architecture—License Server  24 
       

   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 users 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 users 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. 
   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. 
   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. 
   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. 
   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 ). 
   Architecture—Black Box Server  26   
   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 users 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. 
   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. 
   Architecture—User&#39;s Computing Device  14   
   Referring now to  FIG. 4 , in one embodiment of the present invention, the users 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. 
   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. 
   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. 
   DRM System  32   
   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. 
   DRM System  32 —Content Acquisition 
   Acquisition of digital content  12  by a user and/or the users 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. 
   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. 
   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 users 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 . 
   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. 
   DRM System  32 —Content Rendering, Part 1 
   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, Wash., 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. 
   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. 
   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, Wash. 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. 
   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 . 
   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 ). 
   DRM System  32  Components 
   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 . 
   DRM System  32  Components—License Evaluator  36   
   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. 
   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. 
   DRM System  32  Components—Black Box  30   
   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). 
   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. 
   DRM System  32  Components—License Store  38   
   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 . 
   DRM System  32  Components—State Store  40   
   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 . 
   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. 
   DRM System  32 —Content Rendering, Part 2 
   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 ). 
   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. 
   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 unencrypted 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. 
   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 . 
   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. 
   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 users computing device  14 . 
   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 users 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 users 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. 
   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 . 
   DRM System  32 —License Acquisition 
   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). 
   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. 
   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:
         the public key of the black box  30  of the DRM system  32  (PU-BB);   the version number of the black box  30  of the DRM system  32 ;   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 );   the content ID (or package ID) that identifies the digital content  12  (or package  12   p );   the key ID that identifies the decryption key (KD) for decrypting the digital content  12 ;   the type of license  16  requested (if in fact multiple types are available);   the type of rendering application  34  that requested rendering of the digital content  12 ;       

   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 users computing device  14  may be necessary. 
   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 users computing devices  14 , and may refuse to grant any license  16  based on a request from any such bad user and/or bad users 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. 
   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. 
   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. 
   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. 
   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. 
   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. 
   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. 
   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. 
   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 users 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. 
   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:
         the content ID of the digital content  12  to which the license  16  applies;   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));   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));   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   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))).       

   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. 
   Once the digital license  16  has been prepared, such license  16  is then issued to the requester (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 ). 
   It is to be understood that a users computing device  14  may on occasion malfunction, and licenses  16  stored in the license store  38  of the DRM system  32  on such users 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. 
   DRM System  32 —Installation/Upgrade of Black Box  30   
   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 users 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. 
   Preferably, as part of the process of installing the DRM system  32  on a users 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 . 
   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. 
   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. 
   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. 
   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). 
   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. 
   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 users 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. 
   Preferably, the upgraded black box  30  delivered by the black box server  26  is tightly tied to or associated with the users 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 users 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 users 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 . 
   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. 
   DRM System  32 —Content Rendering, Part 3 
   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. 
   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. 
   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 ). 
   Sequence of Key Transactions 
   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. 
   Bearing in mind that each license  16  for the digital content  12 , as seen in  FIG. 8 , includes:
         the content ID of the digital content  12  to which the license  16  applies;   the Digital Rights License (DRL)  48 , perhaps encrypted with the decryption key (KD) (i.e., KD (DRL));   the decryption key (KD) for the digital content  12  encrypted with the black box  30  public key (PU-BB) (i.e., (PU-BB (KD));   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   the certificate that the license server  24  obtained previously from the content server  22  (i.e., (CERT (PU-LS) S (PR-CS))),       

   and also bearing in mind that the package  12   p  having the digital content  12 , as seen in  FIG. 3 , includes:
         the content ID of such digital content  12 ;   the digital content  12  encrypted by KD (i.e., (KD(CONTENT)));   a license acquisition script that is not encrypted; and   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))),       

   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: 
   1. Based on (PU-BB (KD)) from the license  16 , the black box  30  of the DRM system  32  on the users 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. 
   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. 
   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. 
   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. 
   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 users 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. 
   6. Finally, assuming evaluation of the license  16  results in a positive determination that the users 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 ). 
   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 . 
   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 . 
   In particular, in such embodiment: 
   1. the license server  24  provides its public key (PU-LS) to the root entity; 
   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 
   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)). 
   For a DRM system  18  to validate such issued license  16 , then, the DRM system  18 : 
   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 
   2. applies the obtained license server public key (PU-LS) to the signature of the license  16  (S (PR-LS). 
   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-LS 2 ) S (PR-LS 1 )), 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-LS 1 ) S (PR-R)) and a second certificate (CERT (PU-LS 2 ) S (PR-LS 1 )). 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. 
   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. 
   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 . 
   Digital Rights License  48   
   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. 
   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. 
   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 . 
   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 users 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. 
   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 . 
   DRL Languages 
   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;DESCRIPTlON&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;x86Computer&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;/CONTENTSIGNEDSIGNERPUBLICKEY&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;/CONTENTSIGNEDSIGNERPUBLICKEY&gt; 
             
             
               &lt;/SIGNATURE&gt; 
             
             
               &lt;/LICENSE&gt; 
             
             
                 
             
          
         
       
     
   
   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   GUID           of the content       Content Name   Name of the content   String       Content Type   Type of the content   String       Owner Id   ID of the owner of the   GUID           content       Owner Name   Name of the owner of the   String           content       Owner Public Key   Public key for owner of   String           content. This is a base-           64 encoded public key for           the owner of the content.       Licensee Id   Id of the person getting   GUID           license. It may be null.       Licensee Name   Name of the person   String           getting license. It may be           null.       Licensee Public Key   Public key of the   String           licensee. This is the           base-64 encoded public           key of the licensee. It           may be null.       Description   Simple human readable   String           description of the license       Terms   Legal terms of the   String           license. This may be a           pointer to a web page           containing legal prose.       Validity Not After   Validity period of license   Date           expiration       Validity Not Before   Validity period of license   Date           start       Issued Date   Date the license was   Date           issued       DRL Type   Type of the DRL.   String           Example include           ASIMPLE@ or           ASCRIPT@       DRL Data   Data specific to the DRL   String       Enabling Bits   These are the bits that   String           enable 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   GUID           license       Signer Name   Name of person signing   String           license       Signer Public Key   Public key for person   String           signing license. This is           the base-64 encode           public key for the signer.       Content Signed Signer   Public key for person   String       Public Key   signing the 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   String           generate hash. This is a           string, such as AMD5@.       Signature Alg Id   Algorithm used to   String           generate signature. This           is a string, such as ARSA           128@.       Signature   Signature of the data.   String           This is base-64 encoded           data.                    
Methods
 
   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: 
   Access Methods 
   Access methods are used to query a DRL  48  for top-level attributes. 
   VARIANT QueryAttribute (BSTR key) 
   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. 
   DRL Methods 
   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. 
   Boolean IsActivated(Variant data) 
   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. 
   Activate(Variant data) 
   This method is used to activate a license  16 . Once a license  16  is activated, it cannot be deactivated. 
   Variant QueryDRL(Variant data) 
   This method is used to communicate with a more advanced DRL  48 . It is largely about future expandability of the DRL  48  feature set. 
   Variant GetExpires(BSTR action, Variant data) 
   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. 
   Variant GetCount(BSTR action, Variant data) 
   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. 
   Boolean IsEnabled(BSTR action, Variant data) 
   This method indicates whether the license  16  supports the requested action at the present time. 
   Boolean IsSunk(BSTR action, Variant data) 
   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. 
   Enabling Use Methods. 
   These methods are employed to enable a license  16  for use in decrypting content. 
   Boolean Validate (BSTR key) 
   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. 
   int OpenLicense  16 (BSTR action, BSTR key, Variant data) 
   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. 
   BSTR GetDecryptedEnablingBits (BSTR action, Variant data) 
   Variant GetDecryptedEnablingBitsAsBinary (BSTR action, Variant Data) 
   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. 
   void CloseLicense  16  (BSTR action, Variant data) 
   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. 
   Heuristics 
   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: 
   1. Get all licenses  16  that apply to the particular piece of digital content  12 . 
   2. Eliminate each license  16  that does not enable the action by calling the IsEnabled function on such license  16 . 
   3. Eliminate each license  16  that is not active by calling IsActivated on such license  16 . 
   4. Eliminate each license  16  that is not paid for up front by calling IsSunk on such license  16 . 
   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 . 
   6. If there are no licenses  16  left, return status so indicating. The user would then be given the option of: 
   using a license  16  that is not paid for up front, if available; 
   activating a license  16 , if available; and/or 
   performing license acquisition from a license server  24 . 
   Rendering Digital Content on a Portable Device or the Like 
   Referring now to  FIG. 13 , it is to be appreciated that in one mode of obtaining and rendering digital content  12 , such digital content  12  is downloaded or otherwise placed on a personal computer  60  or the like, and the corresponding digital license  16  once obtained is also is downloaded or otherwise placed on the personal computer  60  or the like. Typically, the personal computer  60  or the like is a relatively large and not easily movable device, and requires a power line connection for receiving externally supplied power, and a communications line connection for communicating with the world. In addition, and as was discussed in connection with  FIG. 12 , the computer  60  may include a cable-connected keyboard, a cable-connected mouse, a cable-connected screen, and the like, and may be coupled to a scanner, a printer, and/or other peripheral devices. Thus, the computer  60  is relatively tied down or ‘tethered’ by such connections and peripherals. 
   Of course, the personal computer  60  of  FIG. 13  becomes un-tethered by, for example, disconnecting the peripherals, and becomes more un-tethered by embodying the computer  60  in the form of a full-function lap-top computer having the screen, keyboard, mouse, and a battery power supply built in. Nevertheless, a user wishing to render digital content  12  such as for example a musical selection while for example exercising would certainly balk at carrying such a laptop computer  60  during such activity, even if such lap-top computer  60  weighs only four or five pounds. Moreover, even if such full-function lap-top computer  60  was made to be light-weight, perhaps on the order of two to four ounces, the computer  60  still would contain sensitive components (the hard drive, e.g.) that are likely to be damaged during such activity. 
   Fortunately, and again referring to  FIG. 13 , un-tethered, light-weight, truly portable computing devices  62  exist and can be employed to store and render at least some forms of digital content  12 . For example, the DIAMOND RIO portable music player, marketed by S3 Incorporated of Santa Clara, Calif. is battery-operated, fits in a palm or pocket, has no moving parts, includes large amounts of onboard flash memory to hold digital content  12 , and can render the digital content  12  if for example in the Windows Media Audio (WMA) or the MP3 formats. Such DIAMOND RIO player also is supplied with an appropriate cable and has an interface through which the digital content  12  may be downloaded from the computer  60  by way of the cable. Other portable music players include the RCA Lyra, Creative Nomad II, and Pocket PC devices from Hewlett-Packard, Casio and Compaq. However, and importantly, configuring portable computing devices  62  to support the DRM architecture as set forth above raises several issues. 
   One issue concerns certain players that have relatively small amounts of memory set aside for player operations such as decrypting content, rendering content, and the like. As may be appreciated, with a relatively small amount of memory, a portable device  62  cannot perform at least some DRM functions as were discussed above, such as for example public-private key decryption. A solution responsive to such issue is set forth in U.S. patent application Ser. No. 09/645,887, entitled “Binding Digital Content to a Portable Storage Device Or the Like In A Digital Rights Management (DRM) System” and filed Aug. 25, 2000, hereby incorporated by reference herein in its entirety. 
   However, and importantly, the solution set forth in such U.S. patent application relies on a key system based on a global secret, and such key system is therefore likely globally compromised if and when the global secret is discovered and disseminated. Accordingly, in one embodiment of the present invention, the portable device  62  performs public-private key decryption by way of a portable DRM system  32   p  ( FIG. 13 ) instantiated in a memory thereon. As may be appreciated, such DRM system  32   p  and the accompanying operations such as decrypting content, rendering content, and the like are accommodated on the portable device  62  by increasing the amount of memory on such portable device  62  available, reducing the size of the DRM system  32   p  as instantiated in the memory, or both. 
   In one embodiment of the present invention, and as with the subject matter disclosed in the aforementioned U.S. patent application Ser. No. 09/645,887, all obtaining of digital content  12  and corresponding digital licenses  16  for the portable device  62  is performed by way of a computer  60  or the like. In particular, the computer  60  obtains a license  16  for corresponding digital content  16  and then issues a sub-license  16   s  to the portable device  62  for rendering the digital content  12  on the portable device  62 . Such sub-license  16   s  may be issued in the course of downloading the digital content  12  from the computer  60  to the portable device  62 , or may be issued at a time before or after downloading the digital content  12  from the computer  60  to the portable device  62 , or at another time, all without departing from the spirit and scope of the present invention. Note that although the present invention is discussed in terms of a computer  60  and a portable device  62 , as seen in  FIG. 13 , it will be appreciated that the present invention may be implemented with regard to any particular type of computing device  14  other than the computer  60 , as appropriate, without departing from the spirit and scope of the present invention. 
   Importantly, since the computer  60  performs the bulk of the license acquisition and content acquisition functionality for the portable device  62 , such portable device  62  and the DRM system  32   p  therein need not include such functionality therein, except insofar as is necessary to download the content  12  and the sub-license  16   s . Accordingly, significant license acquisition and content acquisition portions of the DRM system  32  as resident on the computer  60  may be omitted from the DRM system  32   p  as resident on the portable device  62 . 
   The portable device  62  may be defined as a generally closed device in that data can be on-loaded and off-loaded only in a limited manner, user access to hardware within the portable device  62  is very limited, and input and display functionality is limited to a few function keys and perhaps a small LCD screen, respectively. Thus, a content thief can do very little in the way of examining either the memory or physical contents of the portable device  62  to obtain content  12  therein in an unencrypted form or decryption keys. In contrast, the computer  60  may be defined as a generally open device in that data can be on-loaded and off-loaded in a wide-ranging manner by any of a broad range of hardware and/or software, user access to hardware within the portable device  62  is not limited in any significant way, and input and display functionality is available by way of a full-function keyboard, a mouse, a high-resolution monitor, and the like. Thus, a content thief has many potential opportunities available to examine the memory and physical contents of the computer  60  to obtain content  12  therein in an unencrypted form or decryption keys. In sum, then, the portable device  62  as a closed device is less susceptible to nefarious actions committed by a content thief, especially as compared to the computer  60  as an open device. 
   As a result, and also importantly, the portable device  62  and the DRM system  32   p  therein need not include functionality therein necessary to guard against most types of content theft and decryption key theft, except insofar as is necessary during download of the content  12  and the sub-license  16   s . Accordingly, significant theft prevention portions of the DRM system  32  as resident on the computer  60  may be omitted from the DRM system  32   p  as resident on the portable device  62 . 
   To sum up, then, the DRM system  32   p  as resident on the portable device  62  need only include functionality necessary (1) to authenticate the portable device  62  to the computer  60  during downloading of a sub-license  16   s  to the portable device, and to facilitate such downloading, and (2) to render content  12  on the portable device  62  according to downloaded and resident sub-license(s)  16   s , including ensuring that requirements in a sub-license  16   s  are filled and obtaining the content key (KD) from the sub-license  16   s . All other functionality as available in the DRM system  32  on the computer  60  is either unnecessary in the DRM system  32   p  on the portable device  62 , or is inherent in the portable device  62  being a closed device. 
   As may be appreciated, and as was disclosed in the aforementioned U.S. patent application Ser. No. 09/645,887, the sub-license  16   s  as issued by the computer  60  specifies the limitations, if any, that must be satisfied to render the corresponding content  12  on the portable device  62 . Of course, the computer  60  may issue such sub-license  16   s  only if permitted according to the terms of the corresponding license  16  as obtained by the computer  60  from an appropriate license server  24 . As was also disclosed in the aforementioned U.S. patent application Ser. No. 09/645,887, the computer  60  re-writes at least a portion of the license  16  when issuing the sub-license  16   s  to be in a form that is more amenable to the portable device  62  and that ties or binds the sub-license  16   s  to the portable device  62 . In particular, the computer  60  re-encrypts the content key (KD) for decrypting the content  12  into a form that is more amenable to decryption by the portable device  62 . Here, though, the content key is re-encrypted according to the black box public key of the DRM system  32   p  of the portable device  62  (PU-BB-PD). 
   In particular, and assuming that the content key (KD) in the license  16  on the computer  60  is encrypted according to an asymmetric key such as the black box public key of the computer  60  (PU-BB-CO) in the manner discussed above, the computer  60  obtains the content key (KD) by applying the black box private key of the computer  60  (PR-BB-CO) in the manner discussed above, then re-encrypts the content key (KD) according to (PU-BB-PD). Thus, and as should be appreciated, the content key (KD) is obtainable by the portable device  62  at the appropriate time by application of the black box private key of the portable device  62  (PR-BB-PD), and the sub-license  16   s  is therefore tied or bound to the portable device  62 . As should be appreciated, without re-encrypting the content key (KD), the portable device  62 , which would not know (PR-BB-CO), would not be able to decrypt (PU-BB-CO (KD)) to obtain (KD). 
   Delivering the Content  12  and the Sub-License  16 S to the Portable Device  62   
   Referring now to  FIGS. 14 and 15 , then, in one embodiment of the present invention, digital content  12  and a corresponding sub-license  16   s  are downloaded to a portable device  62  according to the following steps. Preliminarily, the portable device  62  must be coupled to an appropriate computer  60  by way of an appropriate connection  64  in the manner shown in  FIG. 13  (step  1401 ). The connection  64  may be any appropriate connection without departing from the spirit and scope of the present invention. Typically, though, the portable device  62  has one or more interfaces  66  and such interface(s)  66  dictate the types of connections  64  that may be employed. For example, the interface  66  may be a serial port, a parallel port, a USB port, a ‘fire wire’ port, an infrared port, or the like, in which case a corresponding type of connection  64  must be employed, assuming the computer  60  supports such connection  64  by way of a corresponding interface  68  and appropriate supporting hardware and/or software. Such connections  64 , interfaces  66 ,  68 , and hardware and/or software in support thereof are known or should be apparent to members of the relevant public and therefore need not be described herein in any further detail. 
   Prior to or after coupling the computer  60  and the computing device  62 , the portable device  62  must obtain the content  12  (step  1403 ). Note that the content  12  may be placed on the portable device  62  directly from an external source, such as by way of an appropriate transferable storage media such as magnetic media, optical media, or electronic media. For example, the storage media may be a micro-size magnetic disk or a ‘memory stick’ with the content  12  already placed thereon by the portable device  62  or another device. Typically, though, and especially in the case where the storage media of the portable device is not transferable, the content  12  is placed thereon by first being placed on the computer  60  and then being transferred from the computer  60  to the portable device  62  by way of the connection  64 . Note that such placement on the computer  60  may be very brief, especially if the computer  60  is obtaining the content  12  directly for the portable device  62 . Obtaining the content  12  and placing such content  12  on the portable device  62 , either by way of the computer  60  or otherwise, is known or should be apparent to members of the relevant public and therefore need not be described herein in any further detail. 
   Also prior to or after coupling the computer  60  and the portable device  62 , the computer  60  must obtain a corresponding license  16  for the content  12  from an appropriate source in the manner set forth above (step  1405 ). Note that the license  16  need not necessarily allow rendering of the corresponding content  12  on the computer  60 . However, such license  16  must allow or at least not prohibit issuance of a corresponding sub-license  16   s  for the portable device  62  and also rendering of the content  12  on the portable device  62 . That is, a licensor may decide for any of a variety of reasons not to allow rendering of its content  12  on a portable device  62 , and therefore prohibit by the terms of a corresponding license  16  issuance of a corresponding sub-license  16   s  for such portable device  62 . Likewise, such licensor may allow issuance of the corresponding sub-license  16   s , but only for certain portable devices  62 . Such licensor may for example specify such sub-license issuance rules in the license  16  to specify the rules of the derived license. 
   Thus, the computer  60  checks the obtained license  16  to determine whether the license  16  in fact allows and does not prohibit issuance of the sub-license  16   s , and perhaps whether the license  16  in fact allows and does not prohibit issuance of the sub-license  16   s  for the portable device  62  (step  1407 ). Such a check of course requires that the portable device  62  communicates identifying information to the computer  60 , and may take any appropriate form without departing from the spirit and scope of the present invention. Assuming the check determines that the sub-license  16   s  may in fact be issued, such issuance proceeds. 
   As seen in  FIG. 15 , the computer  60  thus composes and issues a sub-license  16   s  to the portable device  62  based on the obtained license  16 , wherein the DRM system  32   p  on the portable device  62  renders the corresponding content  12  only in accordance with the terms of the sub-license  16   s  (step  1409 ). In composing and issuing such sub-license  16   s , and as was discussed above, the computer  60  re-encrypts the content key (KD) for decrypting the content  12  from (PU-BB-CO (KD)) to (PU-BB-PD (KD)). 
   In particular, it is to be remembered that according to the DRM architecture, a piece of digital content  12  is encrypted according to a symmetric content key (KD), that the content  12  is to be rendered on a computing device  14  having a black box  30 , that the black box  30  has associated asymmetric public and private keys (PU-BB, PR-BB), that a corresponding license  16  for the content  12  contains the content key (KD) encrypted according to (PU-BB), and therefore that the license  16  is tied or bound to the black box of the computing device  14  and the computing device  14  itself. In issuing a sub-license  16   s  to the portable device  62  for the corresponding content  12 , then, the computer  60  must tie or bind the sub-license  16   s  to the portable device  62  by re-encrypting the content key (KD) therein according to (PU-BB-PD). 
   Thus, the computer  60  performs such re-encryption by:
         1. obtaining (PU-BB-PD) from the portable device  62  (step  1409   a )   2. obtaining the content key (KD) encrypted according to (PU-BB-CO) (i.e., (PU-BB-CO (KD)) from the license  16  (step  1409   b );   3. applying (PR-BB-CO) to (PU-BB-CO (KD)) to obtain (KD) (step  1409   c ); and   4. encrypting (KD) according to (PU-BB-PD) (step  1409   d ). Such (PU-BB-P D(KD)) is then placed in the sub-license  16   s  by the computer  60  (step  1409   e ).       

   It is to be appreciated that in some instances, KD is indirectly encrypted according to PU-BB, by way of an intermediate key. That is, PU-BB encrypts the intermediate key and the intermediate key encrypts KD. Note, though, that KD is still in the original license  16 . More generally, then, and as should be appreciated, the computer  60  performs re-encryption by obtaining the content key (KD) from the license  16  and unsealing same, and then re-sealing KD within the sub-license  16   s.    
   In one embodiment of the present invention, and referring again to  FIG. 13 , the portable device  62  includes a certificate  63  within which is (PU-BB-PD). Thus, and as may now be appreciated, the computer  60  obtains (PU-BB-PD) from the portable device  62  (step  1409   a ) by requesting that the portable device  62  transmit the certificate  63  with such (PU-BB-PD) to the computer  60  and in fact receiving such certificate  63  (step  1409   aa ). The certificate  63  may be signed based on (PR-BB-PD) to verify that the certificate  63  has not been tampered with. The certificate  63  as received by the computer  60  may be compared as against a revocation list  65  to ensure that the certificate  63  has not been compromised (step  1409   ab ). The revocation list  65  may be in the license  16  ( FIG. 15 ), the computer  60  ( FIG. 13 ), or elsewhere. 
   In one embodiment of the present invention, the certificate  63  from the portable device  62  also contains information  67  relating to the portable device  62 . Such information  67  may be any appropriate information without departing from the spirit and scope of the present invention. In one embodiment, such information  67  relates to information that may be employed to determine whether the license  16  allows issuance of the sub-license  16   s  (step  1407 ). For example, the information  67  could include the name, type, and manufacturer of the portable device  62 , the version of the black box  30  on the DRM system  32   p  of the portable device  62 , and the like. As may be appreciated, providing such information  67  to the computer  60  in the form of the certificate  63  provides the license  16  with the ability to specify a wide range of requirements to determine whether to issue the sub-license  16   s  to the portable device  62  based on properties of the portable device  62  itself. 
   If the information  67  is in fact employed to determine whether the license  16  allows issuance of the sub-license  16   s , the certificate  63  must be received (step  1409   aa ) prior to step  1407 . Correspondingly, if the information  67  is in fact employed to determine whether the license  16  allows issuance of the sub-license  16   s , step  1407  includes obtaining the information  67  from the certificate  63  (step  1407   a ) and applying the information  67  to the determination of whether the license  16  allows issuance of the sub-license  16   s  (step  1407   b ) ( FIG. 14A ). As may be appreciated, such determination based on such information  67  may be any desired determination. For example, the determination may include a consideration of whether the manufacturer and/or type of portable device  62  is acceptable, and/or whether the black box  30  on the DRM system  32   p  of the portable device  62  is acceptable, among other things. 
   In composing and issuing the sub-license  16   s , then, the computer  60  generates the sub-license  16   s  from the license  16  by re-writing the license  16  to substitute (PU-BB-PD (KD)) for (PU-BB-CO (KD)), as is seen in  FIG. 15 . In generating the sub-license  16   s , the computer  60  also includes a rights description in the sub-license  16   s  (step  1409   f ,  FIG. 14 ). Such rights description is essentially the rights description set forth within the license  16  (e.g., DRL  48  of  FIG. 8 ). Note that the computer  60  may alter such rights description if necessary or advisable, although no particular rights description alterations are required, generally. Alternatively, the licensor may specify the rights description for the sub-license  16   s  in the license  16 , where the rights description for the sub-license  16   s  is substantially different from and/or separate from the rights description for the license  16 . 
   Once substantively generated, the sub-license  16   s  may be finished by adding a signature to verify the contents of the sub-license  16   s  (step  1409   g ). As may be appreciated, such signature is based on at least a portion of the information in the sub-license  16   s . Accordingly, alteration of such information will cause the signature to fail to verify. The signature may also be based on (PU-BB-PD). 
   As may be appreciated, the steps of  FIG. 14  as discussed above may substantially be performed by a function or set of functions written for and accessible by the DRM system  32  on the computer  60 . Accordingly, such function or functions are actuated upon a user attempting to download content  12  and/or a sub-license  16   s  from the computer  60  to the portable device  62 . 
   Rendering the Content  12  on the Portable Device  62  According to the Sub-License  16 S 
   Referring now to  FIG. 16 , once the portable device  62  has the content  12  and the sub-license  16   s , such portable device  62 , if allowed by the rights description in the sub-license  16   s , may render the content  12  by:
         1. verifying the contents of the sub-license  16   s  based on the signature thereof and (PR-BB-PD) (step  1601 );   2. applying (PR-BB-PD) to (PU-BB-PD (KD)) to obtain the content key (KD) (step  1603 ); and   3. applying (KD) to decrypt the encrypted content  12  (step  1605 ).
 
Checking Out and Checking in Sub-Licenses  16 S
       

   As heretofore described, a computer  60  may issue an essentially unlimited number of sub-licenses  16   s  to multiple portable devices  62 . Note that an arrangement may be made wherein the number of sub-licenses  16   s  issued for a license  16  is stored as state information in the state store  40  ( FIG. 4 ) on the computer  60 , and therefore the DRM system  32  on the computer  60  may keep track of and limit the number of issued sub-licenses  16   s  corresponding to a license  16  according to the terms of such license  16 . Further, such arrangement may be a check-in/check-out arrangement, wherein the stored number increases as sub-licenses  16   s  are ‘checked out’ to portable devices  62  and decreases as sub-licenses are ‘checked in’ from portable devices  62 , and wherein the number has a maximum value as set according to the terms of the corresponding license  16 . 
   As may be appreciated, checking in a sub-license  16   s  comprises removing the sub-license  16   s  from the portable device  62 , and may be accomplished in any appropriate manner without departing from the spirit and scope of the present invention. For example, such checking in may comprise transferring the sub-license  16   s  from the portable device  62  to the computer  60 , deleting the sub-license  16   s  from the portable device  62 , or the like. Such checking in is known or should be apparent to the relevant public and therefore the mechanics thereof need not be discussed herein in any detail. 
   Notably, such a check-in/check-out arrangement can be subverted by copying a checked-out sub-license  16   s  (if possible) from the portable device  62  to a storage device (not shown), checking in the sub-license  16   s  from the portable device  62  to the computer  60 , and re-copying the copied sub-license  16   s  from the storage device (not shown) back to the portable device  62 . In such a situation, the sub-license  16   s  is checked in and yet still available on the portable device  62 . 
   The aforementioned subversion may be avoided by an arrangement wherein information on each sub-license  16   s  checked-out to a portable device  62  is stored as state information in the state store  40  of such portable device  62 . The DRM system  32  on the portable device  62  thus may keep track of each sub-license  16   s  legitimately thereon, and refuse to employ a sub-license  16   s  not noted in the state store  40  thereof and presumably already checked in to the computer  60 . However, such arrangement may overly complicate the DRM system  32   p  on the portable device  62 , and may cause synchronization problems in instances where check-in or check-out transactions are interrupted, for example. 
   In one embodiment of the present invention, such issues are avoided by the use of an arbitrary challenge value or ‘nonce’ during check-out and check-in, where the nonce is to be returned along with another element to signify that the element is legitimate. Any arbitrary nonce may be generated and employed in any appropriate manner without departing from the spirit and scope of the present invention. In particular, and referring now to  FIG. 17 , in the embodiment, check-out of a sub-license  16   s  from the (DRM system  32  of the) computer  60  to the (DRM system  32   p  of the) portable device  62  is achieved by:
         1. requesting, by the computer  60 , a nonce from the portable device  62 , and receiving such nonce (step  1701 );   2. sending, by the computer  60 , the checked-out sub-license  16   s  and the received nonce to the portable device  62  (step  1703 );   3. concluding, by the portable device  62 , that the nonce sent by the computer  60  at step  1703  is the same nonce received by the computer  60  at step  1701  (step  1705 ); and   4. therefore concluding, by the portable device  62 , that the sent sub-license  16   s  that accompanied the sent nonce is legitimate and not from a copied source or elsewhere (step  1707 ).
 
Of course, if the nonces do not match, or if no nonce accompanies a sent sub-license  16   s , the portable device  62  concludes that the sent sub-license  16   s  is not legitimate, and may refuse to store such sent sub-license in the license store  38  of the DRM system  32   p  on the portable device  62 . Thus, the nonce acts as a validating or trust-imparting device for the sent sub-license  16   s.  
       

   Note that the nonce should be bound to the sub-license  16   s . Otherwise, an attacker who intercepts this message could mix and match nonces and licenses. One binding method may be to include the nonce in the signed part of the sub license. 
   As part of checking out a sub-license  16   s , and as will be necessary to check in the checked-out sub-license  16   s , the checked-out sub-license  16   s  is added to a catalog  70  accessible by the DRM system  32  (step  1709 ). Such catalog  70  may for example be stored in the state store  40 . Preferably, and as seen in  FIG. 13 , the catalog  70  includes for each sub-license  16   s  thereon an entry including an identifier identifying the checked-out sub-license  16   s  and an identifier identifying the portable device  62  to which the sub-license  16   s  is checked out. 
   Check-in, then, is achieved by deleting or otherwise removing the checked-out sub-license  16   s  from the portable device  62  and then providing a trusted indication to the computer  60  that the checked-out sub-license  16   s  has in fact been deleted. In particular, check-in of a sub-license  16   s  from the (DRM system  32   p  of the) portable device  62  to the (DRM system  32  of the) computer  60  is achieved by:
         5. deleting, by the portable device  62 , the checked-out sub-license  16   s  therefrom, either by user request or otherwise (step  1711 );   6. requesting, by the portable device  62 , a nonce from the computer  60 , and receiving such nonce (step  1713 );   7. sending, by the portable device  60  to the computer  60 , the received nonce, an identifier identifying the portable device  62 , and a list of all sub-licenses  16   s  currently resident on the portable device  62 , wherein the deleted checked-out sub-license  16   s  is not in the sent list (step  1715 );   8. concluding, by the computer  60 , that the nonce sent by the portable device  62  at step  1715  is the same nonce received by the portable device  62  at step  1713  (step  1717 );   9. therefore concluding, by the computer  60 , that the sent identifier and list that accompanied the sent nonce is legitimate and not from another source (step  1719 );   10. comparing, by the computer  60 , the sent list with the catalog  70 , and noting that the deleted checked-out sub-license  16   s  is in the catalog  70  but not on the sent list (step  1721 ); and   11. deleting the entry having the identifier identifying the deleted checked-out sub-license  16   s  and the identifier identifying the portable device  62  from the catalog  70  (step  1723 ).
 
Thus, the catalog  70  in the state store  40  acts as a library of all checked-out sub-licenses  16   s  for all portable devices  62  that check out sub-licenses  16   s  from the computer  60 , and the presence of an entry that identifies a checked-out sub-license  16   s  acts as a ‘count’ for purposes of counting the number of sub-licenses  16   s  checked out from a particular license  16 . Accordingly, such counting comprises searching the catalog  70  for the number of such checked-out sub-licenses  16   s.  
       

   As with checking out a license, if in the course of checking in a license the nonces do not match, or if no nonce accompanies a sent list and identifier, the computer  60  concludes that the sent list and identifier are not legitimate, and may refuse to check in sub-licenses  16   s  based on the sent list and identifier. Thus, and again, the nonce acts as a validating or trust-imparting device for the sent list and identifier. 
   In the mechanism set out in  FIG. 17 , checking in is not achieved by sending back a sub-license  16   s  from the portable device  62  to the computer  60 . Rather, the sub-license  16   s  is deleted from the portable device  62  and the computer  60  is notified of such deletion in a trusted manner by way of the sent list. As may be appreciated, with such mechanism, the DRM system  32   p  on the portable device  62  need not maintain any particular state information on what sub-licenses  16   s  have been checked-out thereto. Also, by using the catalog  70 , the computer  60  need not maintain count information for each sub-license  16   s  checked out based on each license  16 . 
   CONCLUSION 
   The programming necessary to effectuate the processes performed and modules instantiated 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. 
   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 con tent 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  such as a portable device  62  which is not under the control of the content owner. Further, the present invention comprises a trusted component that enforces the rights of the content owner on such computing device  14  in connection with a piece of digital content  12 , even against attempts by the user of such computing device  14  to access such digital content  12  in ways not permitted by the content owner. 
   It should be appreciated that changes could be made to the embodiments described above without departing from the inventive concepts thereof. In particular, although the present invention has heretofore been described in terms of a portable device  62  attached directly to a PC or computer  60 , where the computer  60  has a license  16  and the license  16  is the basis for a sub-license  16   s  sent to the portable device  62 , the present invention is more broadly defined. 
   For example, the portable device  62  does not in fact have to be portable and may in fact be tethered or too heavy to be moved around. Thus, the device  62  could be another computer or PC while still being within the spirit and scope of the present invention. Moreover, the computer  60  that is the conduit to the ‘portable device’  62  need not necessarily be a PC, but can also be another portable device, or even types of computing devices such as set-top boxes, video consoles, game-playing stations, telephones, appliances, personal digital assistants, and the like. Broadly stated, in the present invention, the sub-license  16   s  may be prepared by any device for any other device and delivered to such other device using the mechanisms described herein. 
   In addition, the device  62  does not have to be connected directly to the computer  60  and may in fact be indirectly connected by way of a network such as a wired or wireless LAN or WAN (e.g., the Internet). Thus, the computer  60  may be any computer on such network or one of several computers on such network. By extension, if the device  62  can receive a sub-license  62  from an arbitrary computer on the network, such device can obtain such sub-license  16   s  directly from a license server  24 . In this case, and as should be appreciated, the sub-license  16   s  is not re-written but is generated directly by the license server  24 . 
   Moreover, although heretofore discussed in terms of a portable device  62 , the sub-license  16   s  may be written directly for portable media that is mounted to such device  62  and that is transferable to other devices  62  and other devices in general. Of course, some alterations are required. Importantly, the portable device identifier is now a portable media identifier, and the sub-license  16   s  is written to be independent of the device  62 . 
   Further, it is to be appreciated that in some instances the sub-license  16   s  is not written or downloaded. Instead, the sub-license  16   s  is implicit (e.g., all content is treated in a particular manner, license-wise), a number of license types are defined on the portable device  62  and each piece of content  12  identifies a license type, or the like. 
   It should be understood, therefore, that the present 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.