Abstract:
In one apparatus, a group of plain text and obfuscated cells of programming instructions is provided to implement a descrambler that descrambles scrambled content to generate descrambled content. In another apparatus, a group of plain text and obfuscated cells of programming instructions is provided to implement an authenticator that provides appropriate authentication challenges to a scrambled content provider, and generates appropriate authentication responses to authentication challenges from the scrambled content provider. In yet another apparatus, a group of plain text and obfuscated cells of programming instructions is provided to implement an integrity verifier that performs integrity verification on a decoder. In yet another apparatus, a group of plain text and obfuscated cells of programming instructions is provided to implement a secrets holder that holds a number of secrets associated with playing scrambled contents.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part application to U.S. patent application, Ser. No. 08/662,679, filed on Jun. 13, 1996, entitled Tamper Resistant Methods and Apparatus, now U.S. Pat. No. 5,892,899 and to U.S. patent application, Ser. No. 08/906,693, filed on Aug. 6, 1997, entitled Cell Array Providing Non-Persistent Secret Storage Through A Mutation Cycle, now U.S. Pat. No. 6,049,609. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of system security. More specifically, the present invention relates to a tamper resistant player for scrambled contents. 
     2. Background Information 
     Content management, such as management of scrambled DVD contents, require the basic integrity of the management operations to be assumed, or at least verified. While a number of security approaches such as encryption and decryption techniques are known in the art, unfortunately, the security approaches can be readily compromised, because these applications and the security approaches are implemented on systems with an open and accessible architecture, that renders both hardware and software including the security approaches observable and modifiable by a malevolent user or a malicious program. 
     Thus, a system based on open and accessible architecture is a fundamentally insecure platform, notwithstanding the employment of security measures. However, openness and accessibility offer a number of advantages, contributing to these systems&#39; successes. Therefore, what is required are techniques that will render the operations of a scrambled content player, such as a DVD player, virtually unobservable or unmodifiable on these fundamentally insecure platforms, notwithstanding their openness and accessibility. 
     SUMMARY OF THE INVENTION 
     In one apparatus, a group of plain text and obfuscated cells of programming instructions is provided to implement a descrambler that descrambles scrambled content to generate descrambled content. 
     In another apparatus, a group of plain text and obfuscated cells of programming instructions is provided to implement an authenticator that provides appropriate authentication challenges to a scrambled content provider, and generates appropriate authentication responses to authentication challenges from the scrambled content provider. 
     In yet another apparatus, a group of plain text and obfuscated cells of programming instructions is provided to implement an integrity verifier that performs integrity verification on a decoder. 
     In yet another apparatus, a group of plain text and obfuscated cells of programming instructions is provided to implement a secrets holder that holds a number of secrets associated with playing scrambled contents. In one embodiment, the secrets include secrets used in a mutual authentication process, and the secrets used for descrambling the scrambled content. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The present invention will be described by way of embodiments, but not limitations, illustrated in the accompanying drawings in which like references denote similar elements, and in which: 
     FIG. 1 is a block diagram illustrating an overview of an exemplary tamper resistant module incorporated with various teachings of the present invention; 
     FIGS.  2 - 3  are two flow charts illustrating one embodiment each of the operational flows, at start-up time and during runtime, of an integrity verification method of the present invention 
     FIG. 4 is a flow chart illustrating one embodiment of the operational flow of an intruder detection method of the present invention; 
     FIGS.  5 - 6  are two flow charts illustrating one embodiment each of the operational flows of two observation detection methods of the present invention; 
     FIG. 7 is a block diagram illustrating one embodiment of a coupling technique of the present invention for inter-coupling various tamper resistant methods; 
     FIG. 8 is a block diagram illustrating one embodiment of a tamper resistant player for scrambled contents, incorporated with the teachings of the present invention; and 
     FIG. 9 is a block diagram illustrating one embodiment of a computer system suitable for practicing the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description, various aspects of the present invention will be described. However, it will be apparent to those skilled in the art that the present invention may be practiced with only some or all aspects of the present invention. For purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the present invention. However, it will also be apparent to one skilled in the art that the present invention may be practiced without the specific details. In other instances, well known features are omitted or simplified in order not to obscure the present invention. 
     Parts of the description will be presented in terms of operations performed by a computer system, using terms such as data, flags, bits, values, characters, strings, numbers and the like, consistent with the manner commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. As well understood by those skilled in the art, these quantities take the form of electrical, magnetic, or optical signals capable of being stored, transferred, combined, and otherwise manipulated through mechanical and electrical components of the computer system; and the term computer system include general purpose as well as special purpose data processing machines, systems, and the like, that are standalone, adjunct or embedded. 
     Various operations will be described as multiple discrete steps in turn in a manner that is most helpful in understanding the present invention, however, the order of description should not be construed as to imply that these operations are necessarily order dependent, in particular, the order of presentation. 
     Referring now to FIG. 1, wherein a block diagram illustrating one embodiment of an exemplary tamper resistant module incorporated with the various teachings of the present invention is shown. As illustrated, exemplary tamper resistant module  100  includes non-tamper resistant portion  102 , and tamper resistant portion  104 . For the illustrated embodiment, the two portions are linked together to form a single executable module. For the purpose of this application, the term module is used in a general sense to mean a structural relationship between the various portions that facilitates exclusive communications between the portions. 
     As described in the parent application, Ser. No. 08/662,679, non-tamper resistant portion  102  includes a number of plain text programming instructions implementing various non-sensitive services of exemplary tamper resistant module  100 , whereas tamper resistant portion  104  includes various groups of plain text and obfuscated cells  106  of programming instructions implementing various sensitive services of exemplary tamper resistant module  100 . Each group of cells that implements a sensitive service or a collection of sensitive services includes at least one plain text cell  106 . Briefly, the secrets associated with the services are distributed in time and space, and obfuscated. The number of obfuscated cells employed to obfuscate a service is service or sensitivity dependent. Generally, the larger number of obfuscated cells employed, the more difficult it will be for the obfuscation to be “decoded”. For a more detailed description, see parent application, Ser. No. 08/662,679. 
     Additionally, in accordance with the present invention, selected groups of plain text and obfuscated cells  106  incorporate a number of tamper resistant measures to verify during operation that exemplary tamper resistant module  100  has not been intruded nor being observed. The number of groups employing these tamper resistant measures, as well as the frequencies and the number of tamper resistant measures employed are also service or sensitivity dependent. As will be described in more details below, these tamper resistant measures include a number of integrity verification measures and a number of anti-observation measures. The integrity verification measures include first integrity verification measure that verifies the integrity of non-tamper resistant portion  102  during run time as well as start-up time, and a second integrity verification measure that verifies an invocation of a group of plain text and obfuscated cells is not originated from an intruder. The anti-observation measures include a first anti-observation measure that verifies the processor executing module  100  is not operating in a mode that supports single step execution, and a second anti-observation measure that verifies elapsed execution times are consistent with normal unobserved execution. 
     FIGS.  2 - 3  illustrate one embodiment of the operational flow of the first integrity verification measure. FIG. 2 illustrates the operational flow at start-up time, whereas FIG. 3 illustrates the operational flow during run time. As shown in FIG. 2, at start-up time, for the illustrated embodiment, a group of cells (GOC) incorporated with this first integrity verification measure scans non-tamper resistant portion  102  and calculates a signature for non-tamper resistant portion  102 , block  108 . Next, for the illustrated embodiment, the GOC retrieves a signature pre-stored for non-tamper resistant portion  102 , block  110 . The GOC then compares the two signatures to verify the generated signature, blocks  112 - 114 . If the generated signature is successfully verified, meaning that non-tamper resistant portion  102  has not been modified, the GOC allows the start-up process to continue, without skipping any verification dependent operations, block  116 , otherwise, the GOC causes the start-up process to continue, skipping the verification dependent operations, block  118 . An example of verification dependent operations is operations associated with setting up the secrets required for delivering certain sensitive services. 
     As shown in FIG. 3, at a verification check time during run time, for the illustrated embodiment, a GOC incorporated with this first integrity verification measure scans a next portion of non-tamper resistant portion  102  and incrementally calculates a signature for non-tamper resistant portion  102 , block  120 . The GOC then updates the signature being incrementally calculated, block  122 . Next, the GOC checks if the end of non-tamper resistant portion  102  has been reached, block  124 . If the end has not been reached, the process terminates, otherwise the process continues at block  126 . 
     At block  126 , the GOC retrieves a signature pre-stored for non-tamper resistant portion  102 , block  126 . The GOC then compares the two signatures to verify the generated signature, blocks  128 - 130 . If the generated signature is successfully verified, meaning that non-tamper resistant portion  102  has not been modified, the GOC allows execution of module  100  to continue, otherwise, the GOC causes execution of module  100  to terminate, block  132 . Causing module to terminate may be achieved in any number of ways known in the art. Depending on the application, it may be preferable to cause the module to fail further downstream from the point the non-tamper resistant portion&#39;s integrity failed verification. 
     In other words, the run time integrity check is performed incrementally over a number of verification check times during an execution run. Those skilled in the art will appreciate the incremental approach is particularly useful for performance sensitive services. The number of verification check times employed for an execution run is service or sensitivity dependent. 
     FIG. 4 illustrates one embodiment of the operational flow of the second integrity verification measure. At invocation time, for the illustrated embodiment, a GOC incorporated with this second integrity verification measure retrieves a return address for the invocation, block  134 . For the illustrated embodiment, the GOC determines if the return address is within the address space of module  100 , block  136 . If the return address is within the address space of module  100 , meaning that the invocation did not originate from an intruder, the GOC allows execution of module  100  to continue, block  138 , otherwise, the GOC causes execution of module  100  to terminate, block  140 . Similarly, causing module  100  to terminate may be achieved in any number of ways known in the art. Depending on the application, it may be preferable to cause the module to fail further downstream from the point the intrusion is detected. 
     FIG. 5 illustrates one embodiment of the operational flow of the first anti-observation measure. At a pre-selected point in time during an execution run, for the illustrated embodiment, a GOC incorporated with this first anti-observation measure retrieves a processor execution mode state variable, block  142 . For the illustrated embodiment, the GOC determines if the state variable denotes an execution mode that supports single step execution, e.g. a debug mode, block  144 . If the state variable denotes an execution mode that does not support single step execution, meaning that execution of module  100  is not being observed, the GOC allows execution of module  100  to continue, block  146 , otherwise, the GOC causes execution of module  100  to terminate, block  148 . Similarly, causing module to terminate may be achieved in any number of ways known in the art. Depending on the application, it may be preferable to cause the module to fail further downstream from the point observation is detected. The number of times as well as the precise points in time during an execution run where the processor&#39;s execution mode is checked is service or sensitivity dependent. 
     FIG. 6 illustrates one embodiment of the operational flow of the second anti-observation measure. At a pre-selected point in time during an execution run, for the illustrated embodiment, a GOC incorporated with this second anti-observation measure retrieves a timer value from the processor executing module  100 , and records the retrieved timer value (timestamp), block  150 . The GOC then continues to perform the normal services it is designed to provide, block  152 . At a pre-selected later point in time, the GOC checks an amount of elapsed execution time since the last timestamp to determine if the amount of elapsed execution has exceeded a predetermined threshold, blocks  154 - 156 . If the elapsed execution time does not exceed the predetermined threshold, meaning that execution of module  100  is not being observed (e.g. by setting breakpoints), the GOC allows execution of module  100  to continue, block  158 , otherwise, the GOC causes execution of module  100  to terminate, block  160 . Similarly, causing module to terminate may be achieved in any number of ways known in the art. Depending on the application, it may be preferable to cause the module to fail further downstream from the point observation is detected. The number of times as well as the precise points in time during an execution run where the amount of elapsed execution time since a last timestamp is checked is service or sensitivity dependent. 
     FIG. 7 illustrates one embodiment of a coupling technique for inter-coupling tamper resistant measures. As illustrated, the different tamper resistant measures are inter-coupled by having the measures share a common storage location, e.g. in memory, for key values associated with the various tamper resistant measures. For the illustrated embodiment, a GOC stores a key for retrieving secrets in portion  162  of storage location  168 , and a timestamp for determining whether execution of module  100  is being observed in storage location  168  less portion  162 . In determining elapsed execution time, the GOC only employs the bits higher than portion  162 . Additionally, the GOC uses lower order bits  164  as a seed to generate the pseudo random numbers employed in an authentication process. Thus, if an intruder attempts to modify the timestamp to defeat the elapsed execution time check measure, it will cause the authentication process as well as any attempt to retrieve secrets to fail. Similarly, if an intruder attempts to modify the seed for generating pseudo random number to defeat the authentication process, it will cause the elapsed execution time check as well as any attempt to retrieve secrets to fail. 
     FIG. 8 illustrates one embodiment of a tamper resistant player for scrambled content applying the tamper resistant teachings of the present invention. As shown, for the illustrated embodiment, tamper resistant player  170  includes non-tamper resistant components  171  and tamper resistant decoder  172 . Non-tamper resistant components  171  are intended to represent a broad category of general service components, such as end user interfaces. These general service components may provide any one of a number of variety of services, implemented using any one of a number of variety of techniques known in the art. Tamper resistant decoder  172  receives scrambled compressed content, and in response, descrambles as well as decompresses the content to output appropriate signals to render the content, e.g. YUV video and AC3 audio. 
     Tamper resistant decoder  172  includes non-tamper resistant portion  175 , tamper resistant portion  174 ,  176 ,  178  and  180 , and signature  173  for non-tamper resistant portion  175 . Non-tamper resistant portion  175  is constituted with plain text programming instructions, whereas tamper resistant portion  174 ,  176 ,  178  and  180  is constituted with multiple groups of plain text and obfuscated cells of programming instructions. Non-tamper resistant portion  175  and tamper resistant portion  174 ,  176 ,  178  and  180 , including signature  173 , are structurally related to facilitate exclusive communication between the portions. For the illustrated embodiment, the two portions are linked together as a single executable module. 
     Non-tamper resistant portion  175  selectively invokes the services of integrated tamper resistant portion  174 ,  176 ,  178  and  180  to effectuate descrambling of the scrambled content, including causing player  170  and a scrambled content provider device to be mutually authenticated with one another. Non-tamper resistant portion  175  decompresses the unscrambled compressed content to generate the above described output signals. Signature  173  is pre-stored in a predetermined location to facilitate start-up time and run time integrity verification as described earlier. 
     For the illustrated embodiment, tamper resistant services of tamper resistant decoder  172  includes tamper resistant descrambler  174  for receiving scrambled content, and in response, descrambling the scrambled content to generate the descrambled content for non-tamper resistant portion of decoder  172 . In one embodiment, tamper resistant descrambler  174  employs secret keys retrieved from tamper resistant secrets holder  180  to descramble the scrambled content. The number of secret keys employed, and the nature of the keys are application dependent, and they are not essential to the understanding of the present invention. Tamper resistant descrambler  174  is constituted with a group of plain text and obfuscated cells of programming instructions. In one embodiment, the core descrambling service is disposed in a plain text cell to provide enhanced performance. In one embodiment, the GOC is equipped with the above described intruder detection integrity verification measure and the single step execution mode detection anti-observation measure. In one embodiment, the GOC is also equipped with the elapsed execution time detection anti-observation measure. In one embodiment, the GOC is equipped with multiple ones of the elapsed execution time detection anti-observation measure. In one embodiment, the elapsed execution time detection anti-observation measure is also inter-coupled with the process for retrieving the secret keys associated with descrambling scrambled content, and the authentication process for mutually authenticating player  170  and a scrambled content provider device. 
     For the illustrated embodiment, tamper resistant services of tamper resistant decoder  172  also includes tamper resistant authenticator  176  for authenticating tamper resistant player  170  to a scrambled content provider device and to authenticate the scrambled content provider device to tamper resistant player  170 . In one embodiment, tamper resistant authenticator  176  employs secret keys retrieved from tamper resistant secrets holder  180  to conduct the authentication process. The number of secret keys employed, and the nature of the keys are application dependent, and they are not essential to the understanding of the present invention. In one embodiment, tamper resistant authenticator  176  is constituted with a group of plain text and obfuscated cells of programming instructions. In one embodiment, the GOC is equipped with the above described intruder detection integrity verification measure, and the single step execution mode detection anti-observation measure. In one embodiment, the GOC is also equipped with the elapsed execution time detection anti-observation measure. In one embodiment, the GOC is equipped with multiple ones of the elapsed execution time detection anti-observation measures. In one embodiment, the elapsed execution time detection anti-observation measure is also inter-coupled with the process for retrieving the secret keys associated with descrambling scrambled content, and the authentication process for mutually authenticating player  170  and a scrambled content provider device. 
     For the illustrated embodiment, tamper resistant services of tamper resistant decoder  172  also includes tamper resistant integrity verifier  178  for integrity verifying non-tamper resistant portion of decoder  172  at start-up time, and during run time. In one embodiment, tamper resistant integrity verifier  178  provides secret keys to be employed for mutually authenticating player  170  and a scrambled content provider device to secrets holder  180 . The number of secret keys employed, and the nature of the keys are application dependent, and they are not essential to the understanding of the present invention. In one embodiment, tamper resistant integrity verifier  178  is constituted with a group of plain text and obfuscated cells of programming instructions. In one embodiment, the GOC is equipped with the single step execution mode detection anti-observation measure. In one embodiment, the GOC is also equipped with the elapsed execution time detection anti-observation measure. In one embodiment, the GOC is equipped with multiple ones of the elapsed execution time detection anti-observation measures. In one embodiment, the elapsed execution time detection anti-observation measure is also inter-coupled with the authentication process for retrieving the secret keys associated with descrambling scrambled content, and the authentication process for mutually authenticating player  170  and a scrambled content provider device. 
     Lastly, as alluded to, for the illustrated embodiment, tamper resistant services of tamper resistant decoder  172  includes tamper resistant secrets holder  180  for storing secrets associated with descrambling scrambled content. Secrets holder  180  also stores secrets associated with an authentication process for authenticating tamper resistant player  170  to a scrambled content provider device and to authenticate the scrambled content provider device to tamper resistant player  170 . In one embodiment, tamper resistant secrets holder  180  is constituted with a group of plain text and obfuscated cells of programming instructions in a cell array form as described in parent application, Ser. No. 08/906,693. In one embodiment, the GOC is equipped with the above described intruder detection integrity verification measure, and the single step execution mode detection anti-observation measure. In one embodiment, the GOC is also equipped with the elapsed execution time detection anti-observation measure. In one embodiment, the GOC is equipped with multiple ones of the elapsed execution time detection anti-observation measures. 
     Thus, even if player  170  receives its content inputs through an “open” bus, the content is nevertheless protected, as the content will be provided to player  170  over the “open” bus in scrambled form. Furthermore, the secrets associated with descrambling the scrambled content, as well as the programming instructions performing the descrambling are protected from intrusion as well as from observation. Yet, performance sensitive operations, such as the core descrambling service, are not burdened. Lastly, the tamper resistant services, i.e. descrambler  174 , authenticator  176  etc. are highly portable, and may be linked up with any number of decoder implementations. 
     FIG. 9 illustrates one embodiment of a computer system suitable for practicing the present invention. As shown, for the illustrated embodiment, computer system  200  includes processor  202 , processor bus  206 , high performance I/O bus  210  and standard I/O bus  220 . Processor bus  206  and high performance I/O bus  210  are bridged by host bridge  208 , whereas I/O buses  210  and  212  are bridged by I/O bus bridge  212 . Coupled to processor bus  206  is cache  204 . Coupled to high performance I/O bus  210  are system memory  214  and video memory  216 , to which video display  218  is coupled. Coupled to standard I/O bus  220  are disk drive  222 , keyboard and pointing device  224  and DVD-ROM  226 . 
     These elements perform their conventional functions known in the art. In particular, disk drive  222  and system memory  214  are used to store a permanent and a working copy of the tamper resistant application of the present invention, when executed by processor  202 . The permanent copy may be pre-loaded into disk drive  222  in factory, loaded from a distribution medium (not shown), or down loaded from on-line/networked distribution source (not shown). The constitutions of these elements are known. Any one of a number of implementations of these elements known in the art may be used to form computer system  200 . 
     Of course, computer systems of alternate constitutions, including computer systems of alternate architectures may also be employed to practice the present invention. 
     In general, while the present invention have been described in terms of the above illustrated embodiments, those skilled in the art will recognize that the invention is not limited to the embodiments described. The present invention can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of restrictive on the present invention. 
     Thus, a tamper resistant player for scrambled contents has been described.