Patent Publication Number: US-9432184-B2

Title: Provisioning of secure storage for both static and dynamic rules for cryptographic key information

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority as a continuation-in-part application to U.S. patent application Ser. No. 14/048,391, filed on May 15, 2014 and entitled “Secure key access with one-time programmable memory and applications thereof”, which claims priority as a continuation-in-part application to U.S. patent application Ser. No. 12/651,996, filed on Jan. 4, 2010 and entitled “Secure Key Access With One-Time Programmable Memory and Applications Thereof”, which in turn claims priority as a continuation-in-part application to U.S. patent application Ser. No. 12/490,777, filed Jun. 24, 2009 and entitled “Device With Privileged Memory and Applications Thereof,” which claims priority to U.S. Patent Application Ser. No. 61/094,541, filed Sep. 5, 2008 and entitled “Methods for System on a Chip Cryptographic Key Access and Storage”, the entireties of which are incorporated by reference herein. 
     The present application is related to co-pending U.S. patent application Ser. No. 14/614,806, entitled “Dynamic Key and Rule Storage Protection” and filed on even date herewith, the entirety of which is incorporated by reference herein. 
    
    
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates generally to techniques for securing data and, more particularly, techniques for storing and providing access to cryptographic keys and other secret values used to secure data. 
     2. Description of the Related Art 
     The desire to keep media content or other proprietary information secure from unauthorized use (e.g., unauthorized copying, distribution, etc.) is driven by a sector of the population that places little to no value on the intellectual properties rights of others. As such, the battle between creating security systems for digital information and the hackers that attempt to break them continues. 
     This battle is intensifying with the integration of electronic device features being implemented on a single device (e.g., computer with DVD functionality) and is further intensified by video processing hardware being implemented as stand-alone system on a chip (SOC) devices. In many instances, the video processing hardware SOC uses an operating system that allows end users to write their own applications, which means that the user&#39;s application may share the same processors and memory space as the security system. This makes the security operations vulnerable. To reduce the vulnerability, media processing hardware needs to be constrained to performing only specific intended types of cryptographic operations. 
     In addition, media processing devices, which include the media processing hardware SOC, are embedded with licensed secret keys for compliance with one or more of a plurality of media application standards (e.g., BD, DTCP, CPRM, Cable Card, etc.). Typically, such a media application standard includes a revocation mechanism whereby, if a secret key value is made public, the security functions of the compromised devices are revoked and the devices are rendered inoperable. As such, it is highly desirable that the secret keys are stored in such a way that they are not accessible to the firmware of the device (in order to avoid revocation). This is typically done by storing the secret keys in a one-time programmable (OTP) memory. 
     While using OTP memory has become a primary mechanism for storing secret keys within media processing devices, it is not a failsafe approach. For example, a security issue arises when multiple cryptographic clients (e.g., a hardware block that performs a specific cryptographic algorithm such as RSA, TSD, ECC, DMA, etc.) may issue read or write requests to the OTP memory asynchronously and that the requests are not atomic. In addition, as a result of granularity associated with OTP memory large key values are partitioned into smaller blocks, which have special read/write rules that are imposed on every block. Thus, it becomes necessary to associate a macro level restriction on cryptographic clients down to every micro level block access performed by the client. 
     As a specific example, the RSA algorithm can perform a 2048 bit RSA operation, which requires 32 reads of 64 bit blocks from the key store to assemble the exponent. If a key is intended to be used as a 2048 bit exponent, then every 64 bit block read must be associated with the intended purpose of the key; i.e. blocks have to have an attribute indicating which cryptographic client is permitted to access a particular block associated with a larger key. 
     Another security problem is that cryptographic strength often relies on using large keys (e.g., up to 2048 bits for RSA or 256 bits for some AES modes). However, if the large key is used one 64 bit block at a time by a weaker cryptographic client, then large keys may be attacked 64 bits (or less) at a time. Yet another way to attack large keys is to decimate a large key by overwriting portions of the key with 0&#39;s, and then perform the intended operations, but with the remainder of the weakened key. Every time a portion of the key is decimated in this way, the remainder can be determined because portions of the key are now known. 
     Still further, some cryptographic clients have the ability to perform operations at various levels of strength; for example, the RSA algorithm can be configured for variable size modulus or 3DES can be degraded into a DES operation. This can be exploited by a hacker to perform weaker operations and thereby attack large keys with degraded operations. Even further, some cryptographic clients use control words (CWs) and initial vectors (IVs) within the security operations. The integrity of a security system may be attacked by using an unknown CW as an IV in an operation where the clear text and the CW are known, which could be used to reveal the unknown CW value. 
     Another important aspect of maintaining the integrity of cryptographic operations is controlling the destination of the cryptographic operation results. For example, content exported from the SOC poses a far greater risk than content which is retained within the SOC. Yet another mode of attack involves using a key, a CW or an IV to decrypt content instead of encrypting the content. For example the intention may be to encrypt content however a hacker may use a key store value to decrypt the content. 
     In addition to the threat of hackers, the security of the secure content information is at risk from unauthorized public disclosure. For example, if a disgruntled employee posts the algorithm and location of the keys on the Internet, the security of the algorithm is lost. As such, the risk to security systems is not just from outsider breaking the security of the algorithm, but also from an insider intentionally compromising the integrity of the security system. 
     Therefore, a need exists for a security device architecture that at least partially overcomes one or more of the above mentioned security issues. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference symbols in different drawings indicates similar or identical items. 
         FIG. 1  is a schematic block diagram of an embodiment of a media processing device in accordance with the present disclosure; 
         FIG. 2  is a schematic block diagram of an embodiment of a device in accordance with the present disclosure; 
         FIG. 3  is a schematic block diagram of another embodiment of a device in accordance with the present disclosure; 
         FIG. 4  is a logic diagram of an embodiment of a method for accessing a cryptographic key in accordance with the present disclosure; 
         FIG. 5  is a diagram of an example of a request in accordance with the present disclosure; 
         FIG. 6  is a diagram of an example of a rule in accordance with the present disclosure; 
         FIG. 7  is a logic diagram of an embodiment of a method for processing a read access request to a cryptographic key in accordance with the present disclosure; 
         FIG. 8  is a logic diagram of an embodiment of a method for processing a write access request to a cryptographic key in accordance with the present disclosure; 
         FIG. 9  is a logic diagram of an embodiment of a method for interpreting a request to a cryptographic key in accordance with the present disclosure; 
         FIG. 10  is a diagram of an example of a one-time programmable memory in accordance with the present disclosure; 
         FIG. 11  is a schematic block diagram of another embodiment of a device in accordance with the present disclosure; 
         FIG. 12  is a logic diagram of an embodiment of a method for accessing privileged memory in accordance with the present disclosure; 
         FIG. 13  is a logic diagram of an embodiment of a method for processing a read request to access privileged memory in accordance with the present disclosure; 
         FIG. 14  is a logic diagram of an embodiment of a method for processing a write request to access privileged memory in accordance with the present disclosure; 
         FIG. 15  is a logic diagram of an embodiment of a method for interpreting a request to access privileged memory in accordance with the present disclosure; 
         FIG. 16  is a diagram of another example of a one-time programmable memory in accordance with the present disclosure; 
         FIG. 17  is a diagram of an example of a key ladder in accordance with the present disclosure; 
         FIG. 18  is a diagram of an example of a device in accordance with the present disclosure; 
         FIG. 19  is a logic diagram of an embodiment of a method for loading and validating keys and rule sets in accordance with the present disclosure; 
         FIG. 20  is a schematic block diagram of another embodiment of a device in accordance with the present disclosure; 
         FIG. 21  is a diagram of an example of a partitioning of a key store memory and rule set memory into static and dynamic segments in accordance with the present disclosure; 
         FIG. 22  is a logic diagram of an embodiment of a method for partitioning of a key store memory and rule set memory into static and dynamic segments in accordance with the present disclosure; 
         FIG. 23  is a logic diagram of an embodiment of a method for writing a cryptographic key and a corresponding dynamically-generated rule to dynamic segments of a key store memory and rule set memory in accordance with the present disclosure. 
         FIG. 24  is a diagram of an example write operation for storing a cryptographic key and corresponding dynamically-generated rule from a cryptographic client to dynamic segments of a key store memory and rule set memory in accordance with the present disclosure. 
         FIG. 25  is a diagram of an example of a write operation for storing a cryptographic key and corresponding dynamically-generated rule from a key ladder to dynamic segments of a key store memory and rule set memory in accordance with the present disclosure. 
         FIG. 26  is a diagram of an example of a write operation for storing a cryptographic key and corresponding dynamically-generated rule from a hardware key generator to dynamic segments of a key store memory and rule set memory in accordance with the present disclosure. 
         FIG. 27  is a logic diagram of an embodiment of a method for protecting cryptographic keys and corresponding rules during loading from OTP memory using obfuscation and de-obfuscation in accordance with the present disclosure; 
         FIG. 28  is a logic diagram of an embodiment of a method for protecting cryptographic keys and corresponding rules during loading to static segments of a key store memory and a rule set memory using obfuscation and de-obfuscation in accordance with the present disclosure; 
         FIG. 29  is a logic diagram of an embodiment of a method for protecting cryptographic keys and corresponding rules during a read access to static segments of a key store memory and a rule set memory using de-obfuscation in accordance with the present disclosure; 
         FIG. 30  is a diagram of an example of a cyclical redundancy check (CRC) calculation operation during provisioning of an OTP memory storing cryptographic keys and corresponding rules in accordance with the present disclosure; 
         FIG. 31  is a logic diagram of an embodiment of a method for verifying an integrity of a key store memory and a rule set memory during a boot process using calculated CRC values in accordance with the present disclosure; and 
         FIG. 32  is a logic diagram of an embodiment of a method for verifying an integrity of a key store memory and a rule set memory using calculated CRC values in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic block diagram of an embodiment of a media processing device  10  that includes a processing module  12 , a memory switch  14 , main memory  16 , a graphics processing module  18 , graphics memory  20 , a hard disk and/or flash memory  22  (or other non-volatile storage component), and input/output (IO) interfaces  24  and  26 . Each of the IO interfaces  24  and  26  includes an IO register  28  and  30 , respectively. Note that the media processing device  10  may be a computer, a laptop computer, a tablet computer, a smartphone, a video game console, an optical disk player, a portable digital audio/video player, etc. and may include multiple IO interfaces  24  and  26 . Further note that each IO interface  24  and  26  may include a plurality of JO registers  28  and  30 . 
     The processing module  12  may be a single processing device or a plurality of processing devices. Such a processing device may be a microprocessor, microcontroller, digital signal processor, microcomputer, central processing unit (CPU), graphics processing unit (GPU), field programmable gate array (FPGA), programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on hard coding of the circuitry and/or executable instructions. The processing module may have an associated memory and/or memory element, such as the main memory  16 , which may be a single memory device, a plurality of memory devices, and/or embedded circuitry of the processing module. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, cache memory, and/or any device that stores digital information. Note that when the processing module implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory and/or memory element storing the corresponding operational instructions may be embedded within, or external to, the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. Further note that, the memory element stores, and the processing module executes, hard coded and/or operational instructions corresponding to at least some of the steps and/or functions illustrated in  FIGS. 1-32 . 
     In an example of operation, one or more of the IO interfaces  24  and  26  receives an instruction to display a media file (e.g., a video file, an audio file, or a combination thereof). The media file may be from an optical disk, stored in the hard disk and/or flash memory, received from a satellite receiver, received from a cable set top box, streamed wirelessly via a cellular data connection or via a wireless local area network (WLAN), and/or any other source of content data. Note that the one or more of the IO interfaces  24  and/or  26  may receive the media file. The media file is encrypted using a particular encryption program and one or more cryptographic keys as prescribed by one or more media standards. 
     In this example, the processing module  12  coordinates the retrieval of the media file from the main memory  16 , the hard disk and/or flash memory  22 , the IO interface  24  and/or  26 , and/or other source. The encrypted media file may include video data, audio data, video graphics data and/or any other type of data requiring security. The processing module  12  evokes a cryptographic client algorithm (e.g., RSA, DES, etc.) and retrieves a cryptographic key from a secure memory location (e.g., a privileged memory). The secure memory location will be described below with reference to one or more of  FIGS. 2-32 . 
     The processing module  12  decrypts the encrypted data using the cryptographic client algorithm and the cryptographic key to produce decrypted data. The decrypted data is provided the graphics processing module  18 . The graphics processing module  18  may be a graphics card, a graphics engine, a graphics processor, a combination thereof, and/or any other device for rendering video data. In this example, the graphics processing module  18  converts the decrypted data into video data and stores it in the graphics memory  20  for subsequent display. 
     The media processing device  10  has three classes of memory access. The most secure class allows access to the system memory (e.g., main memory  16  and/or the hard disk and/or flash memory  22 ) and to IO devices via the IO interfaces  24  and  26 ; allows access to the graphics memory  20  (e.g., frame buffer); and allows access to the secure memory location. The next level of secure access allows access to the system memory and to IO devices via the IO interfaces  24  and  26 . The third access level allows access to system memory. 
       FIG. 2  is a schematic block diagram of an embodiment of a device that includes a hardware (HW) section  32  (e.g., the processing module  12 , the memory switch  14 , the graphics processing module  18 , IO interfaces  24  and  26 , etc.) and a software (SW) section  34  that is stored in the system memory (e.g., main memory  16  and/or the hard disk and/or flash memory  22 ). The software section  34  includes one or more operating systems (OS)  36 , application programming interface (API) section  38 , an application section  40 , and a privileged section  42 . The software section  34  may be stored in the memory of device (e.g., the main memory  16 , the graphics memory  20 , the hard disk/flash memory  22 , and/or the IO registers  28  and  30  of device  10 ). The privileged section  42  may be within the memory of the device and/or at least partially within a one-time programmable memory. 
       FIG. 3  is a schematic block diagram of another embodiment of the device  10  that includes the hardware section (HW)  32  and the software section (SW)  34 . In this embodiment, the software section  34  includes application section  40 , an operating system  36 , and the privileged section  42 . The application section  40  includes a plurality of user applications  60 , a plurality of system applications  62 , and a plurality of cryptographic client applications  56 - 58 . The plurality of cryptographic applications can implement any of a variety of standard or proprietary cryptographic algorithms, such as AES (advanced encryption standard), DES (data encryption standard), 3DES, Multi-2 encryption, DVB (digital video broadcasting), C2 ( cryptomeria  cipher), CSS (content scramble system), MDMI (HDCP), 1394(M6), RSA, ECC (elliptical curve cryptography), Register, any variations thereof, any further versions thereof, and/or any new encryption standards or techniques. 
     The privileged memory section  42  may be implemented using one or more one-time programmable (OTP) memories, random access memory (RAM), and/or read only memory (ROM). The OTP memory may be used to store a default set of the cryptographic keys and a rule set section  52 . The key store section  50  stores one or more cryptographic keys for one or more of the cryptographic clients in an OTP memory, RAM, and/or ROM. The key store section  50  may include memory blocks, where one or more blocks store a cryptographic key. The rule set section  52  stores rules for accessing the key store section  50 . The various rules will be described in greater detail with reference to at least some of  FIGS. 4-32 . 
     The device of  FIG. 3  also includes an arbitration module  54 , which may be part of the operation system  36 , stored in the privileged memory  42 , and/or a separate module (e.g., a stand-alone state machine, a stand-alone processor, etc.). Regardless of its location, the arbitration module  54  coordinates access to the key store section  50  based on the rule sets in the rule set section  52 . In this manner, access requests must come from authorized firmware components (e.g., real cryptographic clients) and the request must be in a specific manner based on the identity of the requestor as delineated in the rule set. If either fails (e.g., unauthorized requestor (e.g., firmware being manipulated by a hacker) or invalid request manner), the arbitration module  54  will deny the request, ignore the request, or provide random data in response to the request. 
     With such an embodiment, the security of a hardware system and the flexibility of a software system are substantially achieved. For instance, by utilizing a single OTP to store permanent rules for accessing the keys, the vulnerability of a software system is substantially avoided and the inflexibility of a hardware system, which uses hard wired single function for a single standard, is also substantially avoided. 
       FIG. 4  is a logic diagram of an embodiment of a method for accessing a cryptographic key that begins at step  70  where a cryptographic client issues a request to access a cryptographic key of the cryptographic keys stored in the key store section  50 . The request should be in a specific format that includes, in this example, a read/write indication, an address of the at least a portion of the cryptographic key, a source or destination of the cryptographic result, and identification of a cryptographic algorithm corresponding to the cryptographic function if the source is adjacent to the destination and is the key store content is a Key/CW or an IV. The method then proceeds to step  72  where a key store arbitration module  54  determines whether the request to access the cryptographic key is valid. For example, if the request is not from an authorized entity (e.g., firmware implementing a function such as a cryptographic client), the arbitration module will indicate that the request is not valid. As such, a hacker&#39;s attempt to access the key store section will be invalid and will fail as shown at step  76 . 
     If, however, at step  74  the request is determined to be valid, the method continues at step  78  where the arbitration module interprets the request for access to the cryptographic key to produce an interpreted request. This will be described in greater detail with reference to  FIG. 9 . The method continues at step  80  where the arbitration module accesses the rule set section  52  based on the interpreted request to retrieve a rule of the set of rules. An example of a rule will be described with reference to  FIG. 6 . 
     The method continues at step  82  where the arbitration module grants access to the cryptographic key in accordance with the rule. Note that the rule set may indicate that the access is not to be granted, as such, in accordance with the rule includes denying the request, ignoring the request, or providing random data. The method continues at step  84  where, when access to the cryptographic key is granted, the cryptographic client executes a cryptographic function regarding at least a portion of the cryptographic key to produce a cryptographic result. 
       FIG. 5  is a diagram of an example of a request  90  that includes a read/write (R/W) indication  92 , an address  96 , a source  97 , a destination  98 , identity of the cryptographic algorithm  100  (e.g., ID of the cryptographic client), and the cryptographic key type. If the R/W indication  92  is for write request, the request will also include the data  94  (e.g., a cryptographic key, a code word, or an initial vector) to be written. The address section  96  indicates the starting address of a block of x-bits (e.g., 64 bits). 
     The source section  97  indicates an initiator of the cryptographic result and the destination section  98  indicates where the cryptographic result will be sent. The valid sources and destinations include the system main memory (e.g., as a frame buffer (FB)), the key store section, the IO registers, and/or the graphics memory. The cryptographic algorithm being used may be identified as ANY, NONE, AES, DES, 3DES, Multi-2, DVB, C2, CSS, MDMI (HDCP), 1394(M6), RSA, ECC, and/or Register. 
     In an embodiment, an adjacency rule may be used. For instance, when a particular client initiates an encryption operation, the corresponding rule in the rule set section  52  determines what key blocks in the key store section  50  can be accessed. By the improvement a further bit is included in the rule whereby when the rule is implemented, it determines the order in which the key store blocks may be accessed. More restrictively, a particular sequence of blocks is prescribed. Less restrictively, groups of key store blocks are accessed in a prescribed order. 
       FIG. 6  is a diagram of an example of a rule  101  of a set of rules. The rule  101  includes an algorithm section  103 , a source and destination section  105 , and a content section  107 . The algorithm section  103  identifies a valid algorithm that is entitled to access the key store section via a read request and/or a write request. For the given algorithm and request, the destination section  105  indicates one or more valid destinations that this algorithm may send its cryptographic result. The content section  107  identifies a valid cryptographic key type (e.g., a cryptographic key, a control word, and/or an initial vector). 
     In this embodiment, a rule is a group of bits (e.g., 16) which dictates how a corresponding block (e.g., 64 bits) in the key store may be accessed. By default, since all bits in the OTP default to 0, the blocks that have un-initialized rules provide unlimited access (i.e. no restrictions). The rule set section  52  thus contains bit masks associated to key store blocks. The bit mapping for rules is as follows: 
                                 TABLE 1                       Field                              Read Algorithm    See Algorithm List           Write Algorithm   See Algorithm List           Destination   110b = FB               101b = SYS, /IO               011b = Key Store Section 50               000b = No Output           Content Type   1b = CW or Key               0b = IV           Source   110b = FB               101b = SYS, /IO               011b = Key Store Section 50               000b = No Output           Adjacent   0 = Unrestricted               1 = Must Be Adjacent                        
Note: if Algorithm=ANY then bits {8, . . . , 15} of the rule are ignored.
 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Algorithm 
                 Description 
               
               
                   
                   
               
             
            
               
                   
                 ANY 
                 Any Algorithm is permitted  
               
               
                   
                   
                 (note 00000b = default) 
               
               
                   
                 AES 
                 ECB, CBC, CTR, OFB, CFB 
               
               
                   
                 CSS 
                   
               
               
                   
                 DES, 2DES 
                 ECB, CBC 
               
               
                   
                 3DES 
                 ECB, CBC 
               
               
                   
                 Multi-2 
                   
               
               
                   
                 DVB 
                   
               
               
                   
                 C2 
                   
               
               
                   
                 MDMI (HDCP) 
                   
               
               
                   
                 RSA 
                   
               
               
                   
                 ECC 
                   
               
               
                   
                 Register I/F 
                 Register Interface 
               
               
                   
                 Reserved 
                   
               
               
                   
                 Reserved 
                   
               
               
                   
                 NONE 
                 No Algorithm may access block 
               
               
                   
                   
               
            
           
         
       
     
     With respect to an adjacency rule: it provides certain cryptographic clients the ability to write the result of a cryptographic operation back into the key store  50 . This is may be useful in cases where the security system makes use of key ladders (e.g., a structure where a key is used to decrypt an encrypted key, the resulting decrypted key may then be used in a subsequent key ladder step or it may be used to decrypt content) and where the key is used to decrypt content is itself the end product of several cryptographic operations. In this context, the adjacent rule is used to enforce a particular order to be adhered to when deriving the key (i.e. the 1st key must be adjacent to step 1 which must be adjacent to step 2, etc. . . . ) where the last step of the ladder culminates with the key intended to decrypt content. Note that the adjacent rule field may contain more than 1 bit to indicate a range of adjacent locations (e.g., 5 bits to provide 32 adjacent locations). For example, instead of the result or an operation being permitted to be written to just the next (i.e. adjacent) location the rule has extra bits allocated that define the permission to write the result to the next N blocks (i.e. a plurality of adjacent locations). This adds flexibility when dealing with a multi stream system where multiple end keys are calculated using the same ladder. 
       FIG. 7  is a logic diagram of an embodiment of a method for processing a read access request to a cryptographic key that begins at step  110  where the key store arbitration module  54  determines whether the request to read the cryptographic key is valid. This may be done by determining whether the requestor is authorized to make a request in accordance with the rule set stored in the rule set section  52 . If, at step  112 , the arbitration module  54  determines that the request is not valid, the method continues at step  114  where the arbitration module  54  returns a random number. The method then continues at step  116  where the arbitration module  54  provides the cryptographic client access to the random number. 
     If the request is valid, the method continues at step  118  where the arbitration module  54  provides at least a portion of the cryptographic key to the cryptographic client. For example, the key may be stored in multiple blocks of the key store section  52  and the arbitration module provides some or all of the blocks the cryptographic client in response to one request. The method continues at step  120  where the cryptographic client executes the cryptographic algorithm utilizing the at least a portion of the cryptographic key on content data to produce encrypted data or decrypted data. Note that, in an embodiment, even though a cryptographic client may make multiple requests and get portions of the key, it typically will use the entire key for a cryptographic operation. 
       FIG. 8  is a logic diagram of an embodiment of a method for processing a write access request to a cryptographic key that begins at step  122  where the arbitration module determines whether the request to write the cryptographic key is valid. This may be done in accordance with a rule of the rule set stored in the rule set section  52 . If, at step  124  it is determined that the request is not valid, the method continues at step  126  where the request fails silently (e.g., no response is given, the request is ignored), or an error status is provided. 
     If, however, the request is valid, the method continues at step  128  where the arbitration module provides access to a block in the key store section  50  for the at least a portion of the cryptographic key for the cryptographic client. The method continues at step  130  where the cryptographic client executes the cryptographic function to write the at least a portion of the cryptographic key into the block of the key store section  50 . 
       FIG. 9  is a logic diagram of an embodiment of a method for interpreting a request to a cryptographic key that begins at step  140  where the arbitration module  54  identifies a type of cryptographic algorithm from the request to access the cryptographic key. For example, cryptographic algorithms may be grouped into type categories. As a specific example, a first type may include ANY, DES, DVB, C2, CSS, M6, Multi-2, HDCP, Register; a second type may include AES, 3DES, ECC; a third type may include RSA; and a fourth type many include NONE. 
     The method branches at step  142  depending on whether the type of cryptographic algorithm is in a class type of a plurality of class types. If not, the method continues at step  146  where the request is denied. If, however, the type is in a class, the method continues at step  144  where the arbitration module establishes a bit boundary corresponding to the class type for accessing the cryptographic key. For example, If Algorithm={ANY, DES, DVB, C2, CSS, M6, Multi-2, HDCP, Register} then the Key Store may be accessed on a 64 bit boundary; If Algorithm={AES, 3DES, ECC} then the Key Store may be accessed on a 128 bit boundary; If Algorithm={RSA} then the Key Store may be accessed on a 1024 bit boundary; and If Algorithm={NONE} then the Key store may be not be accessed on any boundary. 
       FIG. 10  is a diagram of an example of a one-time programmable memory  150  that includes an OTP register interface  152 , and a plurality of registers associated with the key store section  50 . In an embodiment, the OTP area ( 16 K bits) is used to record Keys, CWs and IVs and various other values organized as 256 blocks of 64 bits each. 
     The OTP register interface  152  corresponds to a set of registers which permit reading or writing of 64 bits at a time into a specific OTP block. For every block there are 2 bits of associated OTP memory (i.e. the Read Lock Out Bits {0 . . . 255} and the Write Lock Out Bits {0 . . . 255}. These bits default to =0 (factory default) and may be programmed one time to =1. Once the bit is set to =1 it may never be re-programmed to a =0. When the corresponding read lock out bit is set form a =0 to a =1 then the associated 64 bit OTP block may never be read via the OTP register interface  152 . When the corresponding write lock out bit is set form a =0 to a =1 then the associated 64 bit OTP block may never be written via the OTP register interface  152 . 
     This is a fundamental interlock required to secure secret values into the hardware device. There are a few scenarios: 
     
       
         
           
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Read  
                 Write  
                   
               
               
                 Lock  
                 Lock  
                   
               
               
                 Out 
                 Out 
                 Use Case 
               
               
                   
               
             
            
               
                 0 
                 0 
                 In this case a block of OTP may be left completely 
               
               
                   
                   
                 unlocked and may be programmed in the field or at 
               
               
                   
                   
                 the factory with non security critical information 
               
               
                 0 
                 1 
                 In this case a block of OTP may be write protected 
               
               
                   
                   
                 but not read protected. A typical use for this 
               
               
                   
                   
                 scenario is to record a MAC address which is not 
               
               
                   
                   
                 secure (i.e. may be read) but should not be 
               
               
                   
                   
                 overwritten. 
               
               
                 1 
                 0 
                 In this case a block of OTP is read protected but 
               
               
                   
                   
                 left writeable. A typical scenario for this is to 
               
               
                   
                   
                 provide a mechanism to revoke a system i.e. allow 
               
               
                   
                   
                 a Key to be over written in the field. 
               
               
                 1 
                 1 
                 In this case a block of OTP is read and write 
               
               
                   
                   
                 protected. A typical scenario for this is to record 
               
               
                   
                   
                 keys within the OTP and disable f/w form ever 
               
               
                   
                   
                 reading or overwriting the key. 
               
               
                   
               
            
           
         
       
     
     Note that even if an OTP block&#39;s read write lock out bits are set the block may still be used by a cryptographic client within the hardware device (i.e. H/W blocks may use the key values to perform a cryptographic operation but the value itself may never be exposed). 
     During the initial writing the cryptographic key to the key store memory at step  50  from the OTP memory  150 , the copy may utilize an obfuscation function. For example, blocks of 64 bits (i.e. Block[j]) which are to be written to the OTP memory  150  (i.e. OTP[i]) are obfuscated using a function comprising symmetric binary operators (OP[n]) and a re-mapping function (i.e. [j]→[i]→[j]). The obfuscation function h( ) may be defined as follows:
 
OTP[ i]=HKB[x]OP[y ]Block[ z]   EQ. 1
 
     The corresponding de-obfuscation function h −1 ( ) implemented between the OTP and the key store section  50  uses the following obfuscation function.
 
KeyStore[ z ]=OTP[ i]OP   −1   [y]HKB[x]   EQ. 2
 
     Note that h( ) is a [j]op[j]→[i] mapping and h−1( ) is a [i]op[j]→[j] mapping which means that the bit ordering in the Block[ ] and the HKB[ ] are different; i.e. if a hacker had access to the Block value and the HKB value then the bit ordering would not correspond. 
     An obfuscation key block may be a 64 bit pattern written into one or more blocks of the OTP. The obfuscation key block may default to 0x0 . . . 0 and may be programmed uniquely per device, or uniquely per customer, or uniquely per product model or may default to 0x0 . . . 0. In addition, the obfuscation key block should have a similar number of 0&#39;s as 1&#39;s (+/−10%) (i.e., a non trivial value) to ensure secure obfuscation. 
     The obfuscation functions may be used to secure the key store loading stage of secure key deployment. It allows for a secure way to embed keys in to the OTP memory  150 . This provides an important operational security mechanism which secures cryptographic values within the OTP and provides some security in the factory environment. 
       FIG. 11  is a schematic block diagram of another embodiment of the device  10  that includes the hardware section (HW)  32  and the software section (SW)  34 . In this embodiment, the software section  34  includes application section  40 , an operating system  36 , and the privileged section  42 . The application section  40  includes a plurality of user applications  60  and a plurality of system applications  62 . 
     The privileged memory section  42 , which may be implemented using one or more one-time programmable memories such as the OTP memory  150 , includes a privileged data section  160  (e.g., one embodiment of the key store section  50 ) and a rule set section  162  (e.g., one embodiment of the rule set section  52 ). The privileged data section  160  stores data that is of a privileged nature and should not be accessible to a user of the device or to a hacker. Such data includes one or more cryptographic keys for one or more of the cryptographic clients, other device security features, etc. The privileged data section  160  may include memory blocks, where one or more blocks store a privileged data element. The rule set section  162  stores rules for accessing the privileged data section  160 . 
     The device  10  of  FIG. 11  also includes the arbitration module  54 , which may be part of the operating system  36 , stored in the privileged memory  42 , and/or a separate module (e.g., a stand-alone state machine, a stand-alone processor, etc.). Regardless of its location, the arbitration module  54  coordinates access to the privileged data section  160  based on the rule set of the rule set section  52 . In this manner, access requests must come from authorized firmware components (e.g., real cryptographic clients, operating system firmware functions, other device security functions, etc.) and the request must be in a specific manner based on the identity of the requestor as delineated in the rule set. If either fails (e.g., unauthorized requestor (e.g., firmware being manipulated by a hacker) or invalid request manner), the arbitration module  54  will deny the request, ignore the request, or provide random data in response to the request. 
       FIG. 12  is a logic diagram of an embodiment of a method for accessing privileged memory that begins at step  164  where the arbitration module  54  receives a request for access to at least a portion of the privileged data of the privileged data section  160 . The method continues at step  165  where the arbitration module  54  accesses the rule set section  162  based on the interpreted request to retrieve a rule of the set of rules. Note that a rule of the set of rules includes an algorithm section that identifies one or more valid algorithms, a destination section that identifies a valid destination, and a content section that identifies a valid privileged data type. 
     The method continues at step  166  where the arbitration module  54  determines whether the request is valid. This may be done by accessing the rule set based on the requestor and the type of request (e.g., read privileged data and/or to write privileged data). In addition, the arbitration module may verify the format of the request to insure that includes a read/write indication, an address of the at least a portion of the privileged data, and an indication regarding use of the privileged data. If any of these checks fail, the request is invalid and the method proceeds to step  170  via step  168 , where the request fails. If, however, the request is valid, the method continues at step  172  where the arbitration module  54  interprets the request to produce an interpreted request. The interpretation will be described in greater detail with reference to  FIG. 15 . The method continues at step  176  where the arbitration module  54  grants access to the at least a portion of the privileged data in accordance with the rule. 
       FIG. 13  is a logic diagram of an embodiment of a method for processing a read request to access privileged memory that begins at step  180  where the arbitration module  54  determines whether the request to read is valid. This may be done by accessing an appropriate rule from the rule set. The method branches at step  182  depending on whether the request is valid. If not, the method continues at step  184  where the arbitration module  54  generates a random number. The method continues at step  186  where the arbitration module  54  outputs the random number as the at least a portion of the privileged data. When the request to read is valid, the method continues at step  188  where the arbitration module  54  outputs the at least a portion of the privileged data. 
       FIG. 14  is a logic diagram of an embodiment of a method for processing a write request to access privileged memory that begins at step  190  where the arbitration module  54  determines whether the request to write is valid. This may be done by accessing an appropriate rule from the rule set. The method branches at step  192  depending on whether the request is valid. If not, the request fails silently at step  194 . When the request to write is valid, the method continues at step  196  where the arbitration module  54  provides access to a block of memory in the privileged memory for the at least a portion of the privileged data. 
       FIG. 15  is a logic diagram of an embodiment of a method for interpreting a request to access privileged memory that begins at step  200  where the arbitration module  54  identifies a type of algorithm from the request (e.g., a system level application, an operating system function, a cryptographic algorithm, etc.). The method continues at step  202  where the arbitration module  54  determines whether the type of algorithm making the current request is within one of the types of algorithms. When it is not, the method continues at step  206  where the request is denied. When the type of algorithm is in a class type of a plurality of class types, the method continues at step  204  where the arbitration module  54  establishes a bit boundary corresponding to the class type. For example, a first class may access the privileged memory a block at a time, a second class may access the privileged memory x-blocks at a time, etc. 
       FIG. 16  is a diagram of another example of one or more OTP memories  210  (analogous to OTP memory  150 ) that includes the privileged data section  160 , an OTP register interface  212 , and a plurality of registers  214 - 216 . In an embodiment, the OTP area (16K bits) is used to record Keys, CWs and IVs and various other values organized as 256 blocks of 64 bits each. The OTP register interface  212  corresponds to the set of registers  214 - 216  which permit reading or write 64 bits at a time into a specific OTP block. For every block there are 2 bits of associated OTP memory (i.e. the Read Lock Out Bits {0 . . . 255} and the Write Lock Out Bits {0 . . . 255}. These bits default to =0 (factory default) and may be programmed one time to =1. Once the bit is set to =1 it may never be re-programmed to a =0. When the corresponding read lock out bit is set form a =0 to a =1 then the associated 64 bit OTP block may never be read via the register interface  212 . When the corresponding write lock out bit is set form a =0 to a =1 then the associated 64 bit OTP block may never be written via the register interface. 
     A further embodiment may include an additional multi-bit field for encrypt/decrypt that specifies whether a cryptographic client is required to perform an encrypt or decrypt operation (e.g., ANY=00, Encrypt=10, Decrypt=01, NONE=11). A least constraining state is the 00 (un-programmed state) and a most constraining state is 11 (None). Another embodiment may include increasing the size of the read and write algorithm field from 4 bits to 6 bits to specify 64 different algorithms, which allows for many more algorithms to be added. 
     In another embodiment, a skip function may be used to reduce the number of one time programming (OTP) steps required to populate a key store section by loading one root key into the key store section and then having the keys for other sections of the key ladder calculated from the root rather than having them all loaded during successive steps of the OTP process. In this way, certain OTP steps are obviated. 
     In yet another embodiment, a repeat function may be used to avoid redundancy. For instance, the OTP block includes an indicator stored with certain of the rules in the rule set section to indicate whether that rule is to be repeated to load it in other locations in the key store ladder. Once again, this obviates the requirement of having an OTP step for every location in the key store ladder. 
     In a further embodiment, an Encrypt/Decrypt rule may be used. In particular, a pair of bits are added to each rule which signify that the client can encrypt and decrypt (00), that the client can do one of encrypt and decrypt (1,0) and (0,1), and that the client can copy, but not encrypt or decrypt, the result to another location in the key store section. 
     In an additional embodiment the adjacency constraint can be expanded to define additional types such as CW/Key, IV, Data, Any, None or other types. 
     In yet a further embodiment, the type constraint can be expanded to define a range of adjacency, not just the immediate next. 
       FIG. 17  is a diagram of an example of a key store section used to implement key ladder in accordance with the present disclosure. In particular, a device  325  (one embodiment of the device  10 ) is shown that incorporates one or more of the functions and features described in conjunction with  FIGS. 1-16 and 18-32 . In particular, the device  325  is used to implement a key ladder for use in conditional access (CA), digital rights management (DRM) or other security application in conjunction with Rivest, Shamir, Adelman (RSA) module  324  and Advanced Encryption Standard (AES) module  326  on a single system on a chip (SOC). In this example, a typical broadcast system key ladder is shown where every deployed CA system has a unique Private RSA key, such as private exponent  302 . The implementation of such a key ladder on an SOC provides an improvement in security and economy since there is now a single SOC device rather than two or more devices with a communication link between them. The key ladder itself provides several architectural security improvements. A side benefit is that DRM&#39;s can be implemented using such a key ladders, the security level is brought up to the standard typically required by CA vendors. The various advantages of the present approach will be apparent to those skilled in the art when presented the discussion that follows. 
     In the example shown, an application, utility or other software supplies encrypted key  334  and encrypted codeword  336  that are decrypted in the key ladder based on private exponent  302  to generate codeword  306 . The codeword  306  is used in this example to descramble an encrypted audio/video (A/V) data  320  such as from a transport stream de-multiplexor (TSD) in digital video broadcast module  328  to generate audio/video data  318  that can be written to a frame buffer memory. 
     In operation, key store memory  300  stores cryptographic keys of the key ladder. This can include prestored keys such as private exponent  302  used by RSA module  302  to extract key  304  from encrypted key  334 . In addition, key store memory  300 , such as key store section  50 , can store key  304 , and codeword  306  generated in AES module  326  by decrypting encrypted codeword  336  based on key  304 . Rule set memory  362 , such as rule set section  52 , stores a set of rules for accessing the cryptographic keys of key store memory  300  used in conjunction with the key ladder. Key store arbitration module  364 , such as arbitration module  54 , operates based on the rules in rules set memory  362  to control access to key store memory  300 . In particular, arbitration module  364  allows reading and writing the keys stored in key store memory  300  only in accordance with the set of rules. Examples of such rules are set forth in conjunction with  FIGS. 4 and 7-9  and otherwise, while specific examples are presented below. 
     In a particular embodiment, there is a different set of rules (constraints) for each of the three portions of the key store memory  300  which dictate how values in that portion may be used. The definition of the ladder is based on rules which are hard coded into one-time programmable (OTP) memory  322 , such as OTP memories  150  and  210 , rather than being hard wired into a chip. These constraints enforce the specific sequence of operations which is equivalent to the security provided by a hard wired key ladder. 
     For instance, private exponent portion of key store memory  300  has constraints which enforce the value to be loaded from OTP memory  322  (Write Rule=OTP), the value may only be used by the RSA module  324  (Read Rule=RSA), the value may only be used as a Key (Type=Key), the RSA operation must read a value E(Key) from the frame buffer (Source=FB) and the result of the RSA calculation (Key=(E(Key)) ^ mod n ) must be written to the key store memory  300  (dest=KS), the RSA operation is a decryption operation (i.e. E/D=D), the location of key  304  must be adjacent to the location of private exponent  302  (adjacent=1). 
     Similarly, the key portion of key store memory  300  has constraints which enforce the value to be the result of an operation of RSA module  324  (Write Rule=RSA), the value may only be used by the AES module  326  (Read Rule=AES), the value may only be used as a key (Type=Key), the AES operation must read a value E(CW) from the frame buffer (Source=FB) and the result of the AES calculation (i.e. CW=AES(E(CW,Key)) must be written to the key store memory  300  (dest=KS), the AES operation must be a Decryption (i.e. E/D=D) the location of codeword  306  must be adjacent to the location of key  304  (adjacent=1). 
     In addition, the codeword portion of the key store memory  300  has constraints which enforce the value to be the result of an operation of AES module  326  (Write Rule=AES), the value may only be used by the DVB module  328  (Read Rule=DVB), the value may only be used as a Key (Type=Key), the DVB operation must decrypt content received from an  110  device (i.e. source=I/O) and the resulting decrypted content must be written to the frame buffer (dest=FB), the DVB operation must be a decryption operation (i.e. E/D=D) and the CW  306  may not be used to derive any further key store locations (adjacent=NONE). 
     The rules can also have fields which allow for de-compression of rule set and key values when loading the rule set memory  362  and key store memory  300 . These constraints are referred to as the SKIP and REPEAT fields and generally permit 1:N mapping of OTP memory  322  storage to key store memory  300  and rule set memory  362 . This allows for more optimum use of OTP memory  322 . Examples of such fields are presented below:
     SKIP: In the example discussed above, note that only the private exponent  302  has a prestored value which is read from the OTP memory  322 . It is typical in key ladders for there to be a root value which is stored within the chip (i.e. persistent) and subsequent values are derived (i.e. have no default value). In this case it would be wasteful to allocate locations in the OTP memory  322  to record default values for other locations in the key store memory and so the SKIP field is used to direct the load module  360  to skip over locations in key store memory  300  that correspond to derived keys (i.e. don&#39;t initialize them).   REPEAT: In the example discussed above, note that the granularity of the key store memory may be different for various algorithms (i.e. DVB  328  uses 64 bit codewords, AES uses 128 bit keys and the RSA may use 1024 bit exponents). In order to accommodate the varying granularity the REPEAT field is used to direct the load module  360  to apply the same rule to multiple locations of rule set memory  362 .   

     As previously discussed, device  325  includes OTP memory  322  for storing the prestored key or keys and the set of rules. Load module  360  controls the loading of key store memory  300  with the prestored key or keys and the rule set memory  362  with the set of rules. In an embodiment of the present disclosure, the set of rules includes a signature rule that defines at signature corresponding to at least one of: the set of rules and the at least one cryptographic key. The validation module  366  validates, based on the signature, the loading of the prestored keys in the key store memory  300  and/or the loading of the rule set memory  362 . Further details regarding this aspect of the present disclosure will be discussed in conjunction with  FIGS. 18 and 19  that follow. 
     While shown in conjunction with descrambling of broadcast A/V data, the key ladder shown could likewise be used for encrypting or decrypting other media data, multimedia data or other data to be protected. In particular, nearly all CA and DRM systems may be expressed as a key ladder (i.e. they may have more or less stages and/or may use different specific algorithms). The reason for this is that such security systems are based on a root of trust philosophy where trust is propagated though various stages from most trusted to less trusted. A key ladder is a natural extension of standard cryptographic philosophy. There are proprietary systems which operate with Smart Cards or Cable Cards and use secret algorithms and undocumented protocols and are usually associated with set top boxes distributed by Broadcasters where the CA system is used to control access to only valid customers. On the other hand, DRM systems are generally based on published standards like AACS, DTCP, CPRM, etc. These systems use standard published algorithms and licensed device keys and are usually associated with consumer electronics devices like players or networked devices which are distributed as retail devices. One thing CA and DRM systems have in common is that they can both be expressed as a key ladder i.e. they have a root key (usually stored in Non Volatile Memory) which is used to cryptographically qualify derived intermediate keys which are then used to qualify final keys which are used to de-scramble A/V content. 
       FIG. 18  is a diagram of an example operation of the device  325  in accordance with the present disclosure. In order to make use of the set of rules and the keys that are stored in OTP memory  322 , these values must be loaded in a high speed random access device such as a static random access memory (SRAM). In this embodiment, rule set memory  362  and key store memory  300  are implemented using one or more such memory devices and load module  360  and validation module  366  are implemented via state machines, however, other hardware devices can be used provided that they can be implemented with an appropriate level of security. 
     An obvious point of attack is the storage of rules and keys. Procedures are put in place to protect against hackers modifying or adding rules or keys. During the loading process, load module  360  reads the OTP memory  322  and determines the number of rules (M), extracts the signature from the signature rule, and then copies the rule set into the rule set memory  362 . Along with the rules, the load module  360  will also determine the number of prestored keys (N) and load the prestored keys into the key store memory  300 . When complete, the load module  360  will report the number of rules M and keys N which have been loaded to software  375 . After the loading is complete, the validation module  366  will receive the signature value from the load module  360  and perform a hardware hash check. For example, the load module  360  can evaluate the signature of the key store memory  300  and the rule set memory  362  and compare it against the signature embedded within the signature rule. If the two signatures do not match the validation module  366  can take action to disable access to the keys and the rule set (e.g. erase the key store memory  300  and the rule set memory  362 ). 
     If the keys and rule set are validated, the validation module  366  will also make the signature value available to a software function  375  to perform a software hash check. The software function  375  can be a separate utility or embedded in the operating system, an application or in other software. Software  375  can be implemented as a process on a single SOC that includes the other components presented in conjunction with  FIG. 17  or can run on another device. Software  375  reads the signature calculated by the load module  360 , the number of rules M and number of keys N, and uses this information to construct a message digest and perform a asymmetric signature of the contents of the key store memory  300  and rule set memory  362 . For example an RSA-based signature check may be defined as:
         Digest=Hash value|#rules|#keys   Signature=Digest mod N          

     This mechanism allows a trusted authority to define correct signature and number of rules and keys have been processed (i.e. to prevent hackers from altering or adding rules or keys). If this second signature check fails, then the software  375  takes action to disable the system. Note: there are various possible hash functions and various possible asymmetrical functions which may be used. 
     The rule set can include the following special rules which are used by the load module  360 :
     End of Rules Rule (EOR): there is a default Rule (ALL Zeros) which defines the end of rules within the OTP memory  322 . This rule is intentionally set be equivalent to the default value of the OTP memory  322  i.e. in an un-initialized chip the 1st rule encountered would be an End Of Rules rule (EOR) indicating there are no rules defined. This mechanism also permits additional rules to be defined after some rules have been defined i.e. the unused space may be used to add additional rules after the chip has been provisioned.   Signature Rule: this is a custom rule which is used to define the signature of the rules and keys stored in OTP memory  322 . It is assumed that a typical attack vector would be for a hacker to attempt to modify the rules in OTP memory  322  and so this mechanism is used to define the expected signature of the contents of the rule set and keys stored into the OTP memory  322  thus providing a mechanism to assure the integrity of rule set and keys as they reside in the OTP memory  322 . The signature algorithms can be CRC32, SHA1, SHA256, or other block codes, checksums or error detection algorithm.   NULL Rule: this rule is provided to define an unused rule which may be used to fill the rule storage in OTP memory  322 , i.e. to disable the ability to add additional rules after provisioning.   

     The device architecture of the present disclosure also provides the option to implement multiple CA and DRM systems on the same system on a chip (SOC). This is an important distinction where a customer could field a system containing a single SOC which is provisioned with keys and key ladders which implement more than one CA or DRM system. This provides the customer with a remarkable economy and flexibility since the CA/DRM systems can share resources and co-exist at the same time. 
     It is common in the CA industry to have breaches of security. The typical response in this situation in prior art removable CA systems is to distribute new smart cards or cable cards to customers. These removable CA systems typically implement a new key ladder or contain new keys. In the system of the present disclosure, an ‘End of Rules’ rule can be implemented that defines un-programmed space in the rule and key areas of the OTP memory  322 . In the case of a security breach, it is feasible to download new rules and new keys to update the OTP memory  322  of previously fielded SOC chips, in effect downloading a new CA or DRM system to previously fielded systems. This provides the customer with a remarkable economy and flexibility since the CA/DRM systems can be renewed without a large expense. The Renewed CA or DRM system may be downloaded to fielded products via various communication channels (for example Cable/Satellite/Terrestrial RF links, the Internet, or via media such as DVD&#39;s and BD disks). 
     It is also common to selectively disable fielded products usually because they have been identified as being used by hackers; this is referred to as revocation. Since the architecture of the present disclosure is based on the contents of OTP memory  322  and these contents can be used to record unique chip ID&#39;s. It is possible to identify and disable individual SOC devices. The hard coded key ladder approach provides new methods for revoking devices i.e.:
         Keys may be changed
           (i.e. without the new key the SOC stops working)   
           Key Ladders may be changed
           (i.e. without the new Ladder the SOC stops working)   
           Signature Check
           (i.e. without the new Signature the SOC stops working)
 
In effect since the architecture of the present disclosure support renewability, this creates new and flexible methods for revoking SOC&#39;s.
   
               

       FIG. 19  is a logic diagram of an embodiment of a method for loading and validating keys and rule sets in accordance with the present disclosure. In particular a method is presented for use in conjunction with one or more functions and features presented in conjunction with  FIGS. 1-18 and 20-32 . In step  400 , at least one cryptographic key is loaded from at least one OTP memory to a key store memory. In addition, a set of rules from the OTP memory is loaded in a rule set memory. The set of rules can include a signature rule that defines a first signature. In step  402 , the first signature is retrieved. In step  404 , the validity of the set of rules stored in the rule set memory the cryptographic key or keys stored in the key store memory is determined. In step  408 , the key store memory and the rule set memory are erased, based on a failed validation of at least one of: the set of rules stored in the rule set memory; and the cryptographic key or keys stored in the key store memory. 
     In step  406 , the number of rules in the set of rules is determined along with the number of cryptographic keys. The first signature, and the number of rules in the set of rules stored in the rule set memory and the number of cryptographic keys stored in the key store memory are passed for further validation, such as a second security check. 
     In an embodiment of the present disclosure, step  404  includes: determining a second signature based on the set of rules stored in the rule set memory, and the at least one cryptographic key stored in the key store memory; comparing the first signature to the second signature; and determining the failed validation when the second signature does not match the first signature. 
     As described above, in some embodiments, the key usage in a key store memory can be enforced through rules programmed in an OTP memory during the chip/device provisioning stage. In such instances, once the OTP memory is programmed, the key storage usage is fixed, or static, through the entire life of the device. However, in many implementations, the application use cases of key values and other privileged data may change curing the device life cycle. Such changes may not be foreseeable during device design and manufacture. Accordingly, one approach is to provision a large number of key store blocks in the OTP memory to accommodate as many use cases as possible. However, in most applications the many of these key store blocks will not be used, thereby leading to an unnecessarily large key store space.  FIGS. 20-26  illustrate a dynamic partitioning scheme to address this problem. For this scheme, the key store memory and rule set memory are implemented at least in part by one or more random access memories, such as SRAM memories. The key store memory is divided into two segments: a static key segment (SKS) and a dynamic key segment (DKS). Likewise, the rule set memory is divided into two segments: a static rule segment (SRS) and a dynamic rule segment (DRS). The SRS is used to store static rules from the OTP memory and the SKS is used to store the keys covered by these static rules. However, it should be noted that while the rules in the SRS are static (that is, cannot be changed), the keys in the corresponding SKS may not be static, and instead may be created or modified during device operation. Thus, the term “static” in “static key segment” alludes to the fact that access to the keys of the SKS is controlled by the static rules of the SRS, rather than implying that the keys themselves are static. In contrast, the DRS is used to store rules that may be dynamically created and/or dynamically changed, and the DKS is used to store keys whose access is controlled by the dynamic rules in the DRS. In either instance, the keys of the SKS and the DKS may be received from a register interface, received from a cipher engine output (e.g., as part of a key ladder operation), obtained from the OTP memory (for the SKS only), and the like. 
     To illustrate, for a key store memory of 512 blocks total, if the rule set from the OTP memory covers 100 blocks, the SKS will be sized to 100 blocks, and the remaining 412 blocks will be used for the DKS. This approach permits the device to accommodate future expansion of key usage without having to provision an OTP memory sized large enough to permit a worst-case scenario and thus incur unused space in OTP memory in many applications. Further,  FIGS. 27-32  illustrate example techniques for ensuring or verifying the integrity of these segmented key store and rule set spaces using obfuscation and cyclical redundancy check (CRC) calculations, as described in greater detail below. 
       FIG. 20  is a schematic block diagram of another embodiment of the device  10  that includes the hardware section (HW)  32  and the software section (SW)  34 . In this embodiment, the software section  34  includes application section  40 , an operating system  36 , and the privileged section  42 . The application section  40  includes the plurality of user applications  60 , a plurality of system applications  62 , and a plurality of cryptographic client applications  56 - 58 . The plurality of cryptographic applications can implement any of a variety of standard or proprietary cryptographic algorithms. The privileged memory section  42  is implemented using one or more one-time programmable (OTP) memories  510 , such as OTP memory  150  or OTP memory  210 , as well as a key store memory  560  and rule set memory  562  implemented in one or more random access memories, such as one or more SRAMs. The OTP memory  510  is to store a set of keys  512  of cryptographic keys or other privileged data for one or more cryptographic keys and a static rule set  514  of rules for accessing the keys of the keys  512 . 
     The device of  FIG. 20  also includes an arbitration module  540  (one embodiment of the arbitration module  54 ), an integrity module  542 , and a loader module  544 , each of which may be part of the operating system  36 , stored in the privileged memory  42 , and/or a separate module (e.g., a stand-alone state machine, a stand-alone processor, etc.). As similarly described above with reference to the arbitration module  54 , the arbitration module  540  coordinates access to the key store memory  560  based on the rules in the rule set memory  562  such that access requests must come from authorized firmware components (e.g., real cryptographic clients) and the request must be in a specific manner based on the identity of the requestor as delineated in the rule set. If either fails, the arbitration module  540  will deny the request, ignore the request, or provide random data in response to the request. 
     The loader module  544  operates during the boot process of the device  10  to copy the keys of the keys  512  in the OTP memory  510  to a static key segment of the key store memory  560  and to copy the rules of the static rule set  514  to a static rule segment of the rule set memory  562 . The loader module  544  further operates to load dynamically generated keys and corresponding rules to the dynamic key segment and the dynamic rule segment of the key store memory  560  and rule set memory  562 , respectively. The operation of the loader module  544  is described in greater detail with reference to  FIGS. 21-26 . 
     The integrity module  542  operates to ensure the integrity of the key store memory  560  and rule set memory  562 . In some embodiments, the integrity module  542  utilizes obfuscation techniques to obfuscate the data stored in one or both of the key store memory  560  and rule set memory  562  so as to prevent access to the secrets contained therein in the event that a hacker is able to obtain access to the key store memory  560  or the rule set memory  562 . Further, in some embodiments, the integrity module  542  utilizes CRC calculations and comparisons to verify the integrity of one or both of the key store memory  560  and the rule set memory  562  to ensure that data contained therein has not been corrupted or otherwise modified without authorization. The operation of the integrity module  542  is described in greater detail with reference to  FIGS. 27-32 . 
       FIG. 21  is a logic diagram of an embodiment of a method for provisioning of the key store memory  560  and the rule set memory  562  of the device of  FIG. 20  in accordance with the present disclosure and  FIG. 22  is a diagram of an example of the provisioning method of  FIG. 21 . As noted above, the cryptographic keys and corresponding rule sets stored in an OTP memory are more effectively used when transferred to an SRAM or other rapidly-accessed RAM. Accordingly, during a boot process, at step  501  the device  10  initializes the key store memory  560  and the rule set memory  562 . This initialization process can include, for example, initializing the RAM used for the memories  560  and  562 , writing default values to the blocks of the memories  560  and  562 , and the like. To illustrate, the initial rules for the DRS  530  can be set to “NONE” so that none of the cryptographic clients may access the key store blocks of the DKS  528 . The method continues to step  502  whereupon the loader module  544  provisions a portion of the blocks of the rule set memory  562  to serve as a static rule segment (SRS)  520  by transferring a copy of the static rule set  514  in the OTP memory  510  to the blocks of the SRS  520  and designating the blocks so occupied as the SRS  520 . As part of this provisioning process, the loader module  544  notes the block storing the final rule of the static rule set  514  as the rule set watermark  522  denoting the end of the SRS  520  (and the start of the corresponding dynamic rule segment). Similarly, at step  503  of the method the loader module  544  provisions a portion of the blocks of the key store memory  560  to serve as a static key segment (SKS)  524  by transferring a copy of the keys  512  in the OTP memory  510  to the blocks of the SKS  524  and designating the blocks so occupied as the SKS  524 , and then noting the block storing the final key of the keys  512  as the key store watermark  526  denoting the end of the SKS  524  (and the start of the corresponding dynamic key segment). 
     At the conclusion of this initialization process, the loader module  544  has provisioned the SRS  520  of the rule set memory  562  to statically store the rule set  514  and provisioned the SKS  524  of the key store memory  560  to store the keys  512  governed by the static rules of the SRS  520 . As such, at block  504  of the method the loader module  544  may provision the remaining blocks of the key store memory  560 , starting at the key store watermark  526 , as a dynamic key segment (DKS)  528  for storing cryptographic keys dynamically generated by hardware for temporary use during operation of the device after boot up, and at step  505  the loader module  544  may provision the remaining blocks of the rule set memory  562 , stating at the rule set watermark  522 , as a dynamic rule segment (DRS)  530  for storing rules for accessing the corresponding dynamic keys of the DKS  528 . 
     Under this segmentation method, the device  10  can accommodate the storage of dynamic keys (that is, keys not intended to persist between power-on cycles of the device) solely in RAM, as opposed to convention implementations whereby the OTP memory is used to store dynamic keys, and thus requiring an excessively large OTP memory in order to accommodate foreseeable dynamic key usage over the life cycle of the device. 
       FIG. 23  is a logic diagram of an embodiment of a method for storage of a dynamically-generated rule in the rule set memory  562  that begins at step  601  with issuance of a write request to store a new cryptographic key or modify a previously-generated key at the key store memory  560 . The component that issues the write request may be, for example, a software component, such as one of the cryptographic clients  56 - 58 , as part of a hardware-implemented or software-implemented key ladder operation, or by a hardware key generation component. At step  602 , the arbitration module  540  verifies whether the request to write the cryptographic key is valid. To illustrate, the arbitration module  540  may enforce one or more alignment requirements to ensure that unauthorized or unintended modification of an existing key in the key store memory  560  is avoided. Due to its dynamic nature, the key blocks of the DKS  528  may be overwritten for efficient key storage usage (as may the key blocks of the SKS  524 ). However, this may introduce certain vulnerabilities that allow an unauthorized entity to reduce the entropy length of the existing key by loading a shorter known key over a portion of the longer key (this being commonly known as key decimation). To avoid this vulnerability, the arbitration module  540  may employ an alignment requirement that ensures that for key types larger than the fixed block size, the index or address of the initial key block of the key being accessed (for either reading or writing) is an integer multiple of the standard size of the key being accessed in terms of block size. That is, the cryptographic key is associated with a cryptographic algorithm having a key size that is an integer multiple of the fixed-size of the fixed-size blocks, and the alignment requirement requires that the key store index represent an integer multiple of the key size. 
     To illustrate, assuming a key block is 64 bits, if a rule for a key in the key store memory  560  specifies a 128 bit key, a read or write request for any of the blocks associated with this key must be aligned to an even number (that is, the initial block addressed or indexed by the request must be an even number). As another example, assuming again a key block size of 64 bits, if a rule for a key in the key store memory  560  specifies a 256 bit key (that is 64 bits*4), a read or write request for any of the blocks associated with this key must be equal to 4*n, where n=0, 1, 2, Similarly, for a key associated with a 1024 bit key (that is, 64 bits*16), a read or write request to any blocks associated with this key must have an index or initial address equal to 16*n, where n=0, 1, 2, . . . . 
     With this alignment requirement enforced, a newly loaded key will not straddle two existing keys in the key store  560  and a newly loaded longer key can replace two or more shorter keys. Moreover, a short key can be loaded into one or more blocks of an existing longer key, but this will not permit decimation of the existing longer key as a different rule will also be generated for the replaced blocks. Thus the modified longer key will be useless to a hacker as different key blocks along the whole key length will have different algorithms or rules and the rule checking performed during the retrieval of the modified longer key will fail due to the different rules being present for the same key. 
     Returning to step  603 , if the arbitration module  540  determines that the request is not valid, the method continues at step  604  where the request fails silently (e.g., no response is given, the request is ignored), false information is provided, or an error status is provided. If, however, the request is valid, the method continues at step  605  where the arbitration module  540  provides access to the necessary one or more blocks of the DKS  528  of the key store memory  560  and the component requesting the storage of the dynamically-generated key executes the cryptographic function to write the dynamically-generated key into the one or more blocks of the DKS  528 . 
     At the same time that the key is stored to the DKS  528 , at step  606  the device stores the appropriate rule for the key in the corresponding set of one or more blocks of the DRS  530  of the rule set memory  562 . In some embodiments, the rule is supplied by a component via an interface, such as the registers of the IO interfaces  24  and  26 . In such instances, the supplied rule is received and then stored to the DRS  530 . In other embodiments, usage information for the key is supplied by a component, and the hardware of the device then generates a rule based on this usage information, and the generated rule is then stored to the DRS  530 . In further embodiments, the key is generated as part of a key ladder operation, and usage information for the key (e.g., the particular cryptographic algorithm to be used) may be based on a static rule from the OTP  510  involved in the key ladder operation 
       FIGS. 24-26  are diagrams of examples of storing a dynamically-generated cryptographic key and corresponding rule to the DKS  528  of the key store memory  560  and the DRS  530  of the rule set memory  562 , respectively, in accordance with the method of  FIG. 23 . In the example of  FIG. 24 , a software-initiated loading of a dynamic key is illustrated. When software (e.g., a cryptographic client) loads a content key into the DRS  530 , the software also has to set the corresponding cryptographic algorithm for the key, the key value itself, and the starting key store index into the interface for the key store memory. Once the interface is loaded with this information, the software can trigger the loading operation, in which case the arbitration module  540  generates the appropriate rule based on indicated algorithm and stores the supplied key into the corresponding one or more blocks of the DKS  528  while loading the generated rule into the corresponding one or more blocks of the DRS  530  at the same time. 
     To illustrate, a cryptograph client using an AES cryptographic operation generates a 128 bit AES key  610  and stores the key  610  to a register interface  612 . Concurrently, the cryptographic client stores an algorithm (ALG) indicator  614  representing the 128 bit AES algorithm to a register interface  616 . Further, the cryptographic client specifies block  200  as the starting key store index for storing the key  610  into a register interface (not shown in this example), and then triggers the write operation. Upon verifying the write operation (including performing an alignment check), the arbitration module  540  accesses the ALG indicator  614  from the register interface  616  and generates a rule for the key  610  based on the algorithm indicated by the ALG indicator  614 . In this example, the rule would have the following attributes (referring to Table 1 above): Write Algorithm=ANY; Read Algorithm=AES; Type=CW; Source=Destination=FB; E/D=ANY (the remaining rule fields are not relevant in this example). The arbitration module  540  stores the key  610  to blocks  200  and  201  (the blocks are 64 bits in this example) in the DKS  528 , and concurrently stores the generated rule  618  to the blocks of the DRS  530  that correspond to blocks  200  and  201  of the DKS  528 . 
     The example of  FIG. 25  illustrates a loading of a dynamically-generated key as a key ladder element key that is part of a key ladder operation. In at least one embodiment, a key ladder element key is identified as such by the Destination field of the corresponding rule. The destination field is “KS SRS” or “KS DRS”, the key is identified as a key ladder element key. In such instances, the adjacency field is redefined thusly: when the destination field has the value “KS SRS”, the corresponding key is defined to be an up-layer key ladder element key, which means that it is not the key for generating content keys for storage in the DKS  528 . In this case, the adjacency will be the actual allowable destination key store location offset from the element key block. Conversely, when the destination field has the value “KS DRS”, the corresponding key is defined to be the last key ladder element key, which will be used to generate the content keys. In such instances the value of the adjacency field will be the read algorithm to be used by the generated content keys, as specified by the corresponding rule accessed from the static rule segment  520 . As such, the arbitration module  540  will enforce that the output content keys can only be routed into the DKS  528  and no adjacency will be used. 
     During the last, or final, key ladder element operation for generating a content key, cipher hardware  620  will receive key ladder input  622  along with the last key ladder codeword  624  from the SKS  524  and an indication of the algorithm (ALG) used in the last key ladder element operation. The key ladder input  622  may comprise algorithm bits (ALG  625 ) obtained from the static rule used for the key ladder operation (as specified by the adjacency field), and which indicate the particular cryptographic algorithm for generated content key. The cipher hardware  620  uses the codeword  624  and the key ladder input  622  to generate a content key  626 , which is supplied to the arbitration module  540 , along with a key store block index and the algorithm bits (ALG  625 ), for storage at one or more blocks of the DKS  528 . Concurrently, the arbitration module  540  generates a rule  628  for accessing the content key  626  based on the algorithm bits (ALG  625 ) provided by the cipher hardware  620  and the key ladder input  622  and stores the generated rule  628  at the corresponding block(s) of the DRS  530 . In this case, the rule would have the following attributes (referring to Table 1 above): Write Algorithm=ANY; Read Algorithm=ALG (that is, ALG  625  from cipher hardware  620 ); Type=CW; Source=Destination=FB; E/D=ANY (the remaining rule fields are not relevant in this example). 
     The example of  FIG. 26  illustrates a loading of a dynamically-generated key from a hardware cryptographic component, such as the identified certified IP component  630 . In this example, the component  630  generates a content key  632  and provides the content key  632  to the arbitration module  540  via a corresponding interface (not shown), along with usage bits  634  that indicate the manner in which the content key  632  is to be used. In one embodiment, the usage bits  634  include data indicating the algorithm, whether the content key  632  is to be used for encryption, decryption, or both, and the length of the key (which may instead be indicated or inferred from the algorithm). In this case, after verifying the write access request (including alignment check), the arbitration module  540  stores the content key  632  at the DKS  528  starting at a specified key block index. Concurrently, the arbitration module  540  uses the usage bits  634  to generate a rule  636  for accessing the content key  632  and stores the generated rule  636  to the corresponding blocks of the DRS  530 . Typically, the arbitration module  540  generates the rule  636  through translation of the usage bits  634  into the corresponding fields of the rule  636  (e.g., as shown in Table 1 above). 
     While the segmentation of the key store memory  560  and the rule set memory  562  into static and dynamic segments permits adaptation to dynamic rule generation and key generation/modification without requiring excessive OTP storage provisioning, the ability to dynamically store and modify keys and rules in non-volatile memory introduces potential vulnerabilities. To illustrate, attackers may attempt to directly retrieve the privileged information along the path where it is used or transferred, or attempt to change the corresponding rules to allow otherwise prohibited usage so that the security of the key store can be compromised.  FIGS. 27-32  describe various mechanisms for the segmented key store and rule set to ensure the secrecy of the privileged information and the integrity of the rules protecting access to the privileged information. 
       FIG. 27  is a logic diagram of an embodiment of a method for protecting the keys  512  and corresponding rule set  514  during transfer from the OTP memory  510  to the key store memory  560  and rule set memory  562  in accordance with the present disclosure. At an initial step  701 , when the OTP memory  510  is being provisioned during initial provisioning of the device  10 , the keys  512  are obfuscated and the obfuscated versions of the keys  512  are stored to the OTP memory  510 . Likewise, the rule set  514  may be obfuscated and the obfuscated versions of the rules of the rule set  514  may be stored to the OTP memory  510  during provisioning. Any of a variety of obfuscation algorithms may be used during this obfuscation process. To illustrate the obfuscation operation represented by EQ. 1 above may be utilized to obfuscate the secrets to be stored to the OTP memory  510 . 
     Subsequently, at step  702  the device  10  initiates a boot process from reset or power-on. In response, at step  703  the integrity module  542  seeds an obfuscation function with a value that is specific to that particular iteration of the boot process. To illustrate, the integrity module  542  may use a randomly generated or pseudo-randomly generated value as a seed value for the obfuscation function. At step  704 , the loader module  544  accesses the keys  512  and rule set  514  so as to transfer copies to the SKS  524  and SRS  520 , respectively, implemented in non-volatile memory of the device  10 . However, prior to storing the copies, at step  704  the integrity module  542  de-obfuscates the obfuscated versions of these values stored in the OTP memory  510  using a reverse-obfuscation algorithm that corresponds to the obfuscation algorithm used at step  701  (e.g., the reverse-obfuscation process represented by EQ. 2 above). At step  705 , the integrity module  542  re-obfuscates the keys  512  using the obfuscation function seeded at block  703  to generate obfuscated versions of the keys  512  for loading into the SKS  524 . Similarly, the rule set  514  can be re-obfuscated using the seeded obfuscation function and the resulting obfuscated version of the rule set  514  can be stored to the SRS  520 . 
     The process described protects the secrets represented by the keys  512  and the rule set  514  by de-obfuscating and re-obfuscating the keys  512  and rule set  514  in a manner particular to each power cycle. In this manner, the scrambled data stored in the SKS  524  and the SRS  520  differs for each time the device  10  is reset, which in turn reduces the likelihood that an attacker can successfully break the obfuscation process and gain access to the unscrambled version of the keys  512  or the rule set  514 . 
       FIG. 28  is a logic diagram of an embodiment of a method for protecting dynamically-generated keys and corresponding rules during storage in the dynamic segments of the key store and rule set memories. At an initial step  701 , a write access request is received from a cryptographic client or other component and the write request is validated by the arbitration module  540 . In response, the verification module  542  obfuscates the key using the obfuscation function seeded at step  703  of the method of  FIG. 27  and stores the obfuscated version of the key in the DKS  528 . This same process may be used to obfuscate the corresponding rule before it is stored in the DRS  530 . As such, if an attacker were to gain unauthorized access to the key store memory  560  or the rule set memory  562 , the attacked would be further thwarted by the secrecy maintained for the information stored therein due to the obfuscation process. 
       FIG. 29  is a logic diagram of an embodiment of a method for read access of obfuscated keys and corresponding rules from the key store and rule set memories in accordance with the present disclosure. The method begins at step  721  with the receipt of read request for a key from the key store memory  560 . After validating the requestor, at step  722  the integrity module  542  de-obfuscates the obfuscated rule for the requested key and the arbitration module  540  validates the request based on the de-obfuscated rule. After validating the request, at step  723  the arbitration module  540  accesses the obfuscated key, the integrity module  542  de-obfuscates the obfuscated key, and the de-obfuscated key is provided to the requestor. 
     As described above, an attacker may attempt to derive a key either through decimation (whereby the entropy of a key is reduced by overwriting a portion of the key with a known value) or through unauthorized modification of the rule so as to give the attacker “authorized” access to the entire key.  FIGS. 30-32  illustrate example mechanisms for detecting such modifications through the use of cyclical redundancy check (CRC) values. 
       FIG. 30  is a diagram of an embodiment of a method for initial calculation of reference CRC value for the secrets stored in an OTP memory during its provisioning in accordance with the present disclosure. As described above, when the device  10  is provisioned, a static set of keys  512  and a corresponding static rule set  514  are stored in the OTP memory  150 . To configure an initial representation of the set of keys  512  and rule set  514  in the OTP memory  150 , a CRC value  801  covering one or both of the set of keys  512  and the rule set  514  is calculated and stored at a designated location of the OTP memory  150 . In some embodiments, one reference CRC value may be generated from the keys  512  and a separate reference CRC value may be generated from the rule set  514 . In the event that the obfuscation techniques described above are used, the CRC value may be calculated using the obfuscated versions of the keys and/or rules. The one or more CRC values  801  generated and stored in this manner thus serve as an initial reference CRC value that may be used to identify any modifications to the values represented by the reference CRC during transfer to the key store/rule set memories. 
       FIG. 31  is a logic diagram of an embodiment of a method for verifying the integrity of the static segments of the key store/rule set memories after initial loading from the OTP memory  150 . The method starts at step  811  with the initiation of a boot process for the device  10 . As part of the boot process, at step  812  the loader module  544  transfers copies of the keys  512  and rule set  514  from the OTP memory  150  to the SKS  524  and the SRS  520 , respectively, as described above. 
     After these values have been transferred, at step  813  the integrity module  542  accesses the CRC value  801  from the OTP memory, and at step  814  the integrity module  542  calculates a second CRC value based on one or both of the keys  512  and the rule set  514  (depending on which values were used to calculate the CRC value  801  in the method of  FIG. 30 ). If there has been no modification or corruption of the values during the copying from the OTP memory to the key store/rule set memories, the CRC value  801  and the second CRC value should be exact matches. Accordingly, at step  815  the integrity module  542  compares the CRC value  801  with the CRC value calculated at step  814 . If there is a match, the integrity of the secrets of the OTP memory  150  have been maintained during the boot process, and thus the device  10  is ready to enter an operational mode with the key store memory  560  at step  816 . 
     Otherwise, if the comparison at step  815  reveals a mismatch, then one or both of the keys  512  or the rule set  514  has been corrupted or compromised. In such instances, at step  817  the arbitration module  540  presents further access to the key store memory  560  and the rule set memory  562 , such as by wiping out at least the key store memory  560  (e.g., by overwriting the entire key store memory  560  with all 1&#39;s or all 0&#39;s), setting a configuration parameter that prevents addressing of any block of the key store memory  560  under any condition, and the like. In this manner, if an attacker is able to corrupt the transfer process so as to reconfigure a static rule or decimate a static key, this corruption is detected through the CRC value mismatch and any further use of the corrupted secret or corrupted rule is prevented. 
       FIG. 32  is a logic diagram of an embodiment of a method for verifying the integrity of one or both of the static segments and dynamic segments of the key store/rule set memories during an operational mode of the device  10  in accordance with the present disclosure. After the initial loading of static keys and rules into the static segments of the key store memory  560  and rule set memory  562 , components are enabled to dynamically generate keys and have these keys and corresponding access rules stored to the dynamic segments of the key store memory  560  and rule set memory  562 , respectively. As such, this prevents another opportunity for an attacker to attempt to corrupt a rule or decimate a key. The method of  FIG. 32  provides a mechanism to provide periodic verification of the integrity of the rule set and the keys through CRC comparisons. The method initiates at step  901  with the detection of a CRC calculation trigger by the integrity module  542  during operation of the device  10  after the boot process. The CRC trigger may be the completion of the boot process (this process being reflected in the method of  FIG. 31 ), a read or write access to the key store memory  560 , or the timeout or lapse of a configurable idle timer set to trigger periodic integrity validation. In response to detecting a CRC calculation trigger, at step  902  the integrity module  542  recalculates a CRC value for at least the rule set memory  562 . In some embodiments, the key store memory  560  may be included in this CRC calculation, or a separate CRC value for the key store memory  560  may be recalculated. 
     At step  903 , the integrity module  542  determines whether the CRC calculation trigger detected at step  901  is a read access trigger or timeout trigger. If not, the method returns to step  901  to await the next detected CRC calculation. However, if the CRC calculation trigger is a read access trigger or timeout trigger, at step  904 , the CRC value calculated at step  902  is compared with the CRC value calculated at a previous iteration of the method of  FIG. 32 . That is, the CRC value calculated at step  902  serves as the reference CRC value for the next iteration of the method of  FIG. 32 . Note that, as represented by step  904 , if the CRC calculation trigger was a write access, a CRC value is calculated for the rule set memory after the write has completed, and this CRC value then serves as the reference CRC for the next iteration of the method. The CRC value calculated in response to a read access trigger or timeout trigger should match the reference CRC. If there is a match, the method returns to step  901  to await the next detected CRC calculation trigger for another iteration of the method. If there is a mismatch, then one or both of the key store memory  560  or the rule set memory  562  have been compromised or corrupted, and thus at step  905  the arbitration module  540  prevents further access to the key store memory  560  and the rule set memory  562 , such as by overwriting them with all 1&#39;s, all 0&#39;s, or random data, or by applying a configuration that prevents addressing any of the blocks of the memories  560  and  562 . 
     As may be used herein, the terms “substantially” and “approximately” provides an industry-accepted tolerance for its corresponding term and/or relativity between items. Such an industry-accepted tolerance ranges from less than one percent to fifty percent and corresponds to, but is not limited to, component values, integrated circuit process variations, temperature variations, rise and fall times, and/or thermal noise. Such relativity between items ranges from a difference of a few percent to magnitude differences. As may also be used herein, the term(s) “coupled to” and/or “coupling” includes direct coupling between items and/or indirect coupling between items via an intervening item (e.g., an item includes, but is not limited to, a component, an element, a circuit, and/or a module) where, for indirect coupling, the intervening item does not modify the information of a signal but may adjust its current level, voltage level, and/or power level. As may further be used herein, inferred coupling (i.e., where one element is coupled to another element by inference) includes direct and indirect coupling between two items in the same manner as “coupled to”. As may even further be used herein, the term “operable to” indicates that an item includes one or more of power connections, input(s), output(s), etc., to perform, when activated, one or more its corresponding functions and may further include inferred coupling to one or more other items. As may still further be used herein, the term “associated with”, includes direct and/or indirect coupling of separate items and/or one item being embedded within another item. As may be used herein, the term “compares favorably”, indicates that a comparison between two or more items, signals, etc., provides a desired relationship. For example, when the desired relationship is that signal  1  has a greater magnitude than signal  2 , a favorable comparison may be achieved when the magnitude of signal  1  is greater than that of signal  2  or when the magnitude of signal  2  is less than that of signal  1 . 
     The present disclosure has also been described above with the aid of method steps illustrating the performance of specified functions and relationships thereof. The boundaries and sequence of these functional building blocks and method steps have been arbitrarily defined herein for convenience of description. Alternate boundaries and sequences can be defined so long as the specified functions and relationships are appropriately performed. Any such alternate boundaries or sequences are thus within the scope of the claimed invention. 
     The present disclosure has been described above with the aid of functional building blocks illustrating the performance of certain significant functions. The boundaries of these functional building blocks have been arbitrarily defined for convenience of description. Alternate boundaries could be defined as long as the certain significant functions are appropriately performed. Similarly, flow diagram blocks may also have been arbitrarily defined herein to illustrate certain significant functionality. To the extent used, the flow diagram block boundaries and sequence could have been defined otherwise and still perform the certain significant functionality. Such alternate definitions of both functional building blocks and flow diagram blocks and sequences are thus within the scope of the claimed invention. One of average skill in the art will also recognize that the functional building blocks, and other illustrative blocks, modules and components herein, can be implemented as illustrated or by discrete components, application specific integrated circuits, processors executing appropriate software and the like or any combination thereof. In some embodiments, certain aspects of the techniques described above may implemented by one or more processors of a processing system executing software. The software comprises one or more sets of executable instructions stored or otherwise tangibly embodied on a non-transitory computer readable storage medium. The software can include the instructions and certain data that, when executed by the one or more processors, manipulate the one or more processors to perform one or more aspects of the techniques described above. The non-transitory computer readable storage medium can include, for example, a magnetic or optical disk storage device, solid state storage devices such as Flash memory, a cache, random access memory (RAM) or other non-volatile memory device or devices, and the like. The executable instructions stored on the non-transitory computer readable storage medium may be in source code, assembly language code, object code, or other instruction format that is interpreted or otherwise executable by one or more processors. 
     A computer readable storage medium may include any tangible, non-transitory storage medium, or combination of tangible, non-transitory storage media, accessible by a computer system during use to provide instructions and/or data to the computer system. Such storage media can include, but is not limited to, optical media (e.g., compact disc (CD), digital versatile disc (DVD), Blu-Ray disc), magnetic media (e.g., floppy disc, magnetic tape, or magnetic hard drive), volatile memory (e.g., random access memory (RAM) or cache), non-volatile memory (e.g., read-only memory (ROM) or Flash memory), or microelectromechanical systems (MEMS)-based storage media. The computer readable storage medium may be embedded in the computing system (e.g., system RAM or ROM), fixedly attached to the computing system (e.g., a magnetic hard drive), or removably attached to the computing system (e.g., an optical disc or Universal Serial Bus (USB)-based Flash memory). 
     Note that not all of the activities or elements described above in the general description are required, that a portion of a specific activity or device may not be required, and that one or more further activities may be performed, or elements included, in addition to those described. Still further, the order in which activities are listed are not necessarily the order in which they are performed. Also, the concepts have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present disclosure as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present disclosure. 
     Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims. Moreover, the particular embodiments disclosed above are illustrative only, as the disclosed subject matter may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. No limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the disclosed subject matter. Accordingly, the protection sought herein is as set forth in the claims below.