Abstract:
An improved secure programming technique involves reducing the size of bits programmed in on-chip secret non-volatile memory, at the same time enabling the typical secure applications supported by secure devices. A technique for secure programming involves de-coupling chip manufacture from the later process of connecting to ticket servers to obtain tickets. A method according to the technique may involve sending a (manufacturing) server signed certificate from the device prior to any communication to receive tickets. A device according to the technique may include chip-internal non-volatile memory to store the certificate along with the private key, in the manufacturing process.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This Divisional Application claims priority to U.S. patent application Ser. No. 11/601,323, filed Nov. 16, 2006, entitled METHOD FOR PROGRAMMING ON-CHIP NON-VOLATILE MEMORY IN A SECURE PROCESSOR, AND A DEVICE SO PROGRAMMED, which claims priority to U.S. Provisional Patent Application No. 60/857,840, filed Nov. 9, 2006, entitled METHOD FOR PROGRAMMING ON-CHIP NON-VOLATILE MEMORY IN A SECURE PROCESSOR, AND A DEVICE SO PROGRAMMED and each of the aforementioned applications is incorporated in its entirety. 
     
    
     BACKGROUND 
       [0002]    A secure processor typically includes an ID and/or stored secret key. In order to enhance the level of security, the quantities could be programmed in chip-internal non-volatile memory to build a secure processor. The programming of the ID and secret key happen during the secure manufacturing process of the chip. Each ID is unique, and so is the private key. These quantities are used in applications on the device, to implement digital rights management and other security related applications. Typically, the chip includes mechanisms to generate cryptographically strong random numbers to use as nonces in network protocols, secret keys etc. 
         [0003]    In a typical infrastructure used for implementing digital rights management, a server is used to supply digitally signed tickets to enable rights for the device. Such tickets use the device identities and/or secret key mechanisms to bind the tickets to the devices. In order to ensure the uniqueness of each device ID/key the server typically uses a secure database to store the IDs, (and/or signed certificates) corresponding to each chip that is manufactured. These certificates contain public keys corresponding to each secret key (private key of a (private, public) key pair) programmed in the chip. In order to populate the database with certificates, the infrastructure associated with the database should be securely coupled with the manufacturing process to maintain a one-to-one correspondence between manufactured chips and certificates in the database. 
         [0004]    The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings. 
       SUMMARY 
       [0005]    The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools, and methods that are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements. 
         [0006]    An improved secure programming technique involves reducing the size of bits programmed in on-chip secret non-volatile memory, at the same time enabling the typical secure applications supported by secure devices. Another improved secure programming technique involves simplifying the process of manufacture of the system. In an embodiment, programming the secrets is isolated to on-chip programming, and, specifically, is isolated from the processes of system integration and infrastructure setup. 
         [0007]    A technique for secure programming involves de-coupling chip manufacture from the later process of connecting to ticket servers to obtain tickets. A method according to the technique may involve sending a (manufacturing) server signed certificate from the device prior to any communication to receive tickets. The method may further include populating a database to facilitate performing ticket services later, for example just when the ticket services are needed. 
         [0008]    A device according to the technique may include chip-internal non-volatile memory to store the certificate along with the private key, in the manufacturing process. The private key may or may not be an elliptic curve based private key. An advantage of the elliptic curve cryptography based key is that it is smaller than many other types of keys for the relative cryptographic strength. Further, it is possible, using elliptic curve algorithms, to store a random private key and compute the public key by a run-time computation. 
         [0009]    Advantageously, especially considering the value of on-chip real estate, a compressed certificate can be provided in the non-volatile memory. Using a smaller data-set (than what would be required to store a device certificate) the device dynamically generates a certificate on the device, to provide to a requesting application. The device certificate may or may not be generated multiple times. For example, the device certificate could be generated once and stored in system external storage for further use. This is not particularly insecure because the certificate is public data. 
         [0010]    A device constructed according to the technique may have applicability in other areas. For example, the device could be authenticated to a peer, or to any application that requires a first device certificate. In another alternative, the non-volatile memory may include a secure random number generator for the device, using the secure manufacturing process to program the non-volatile memory. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Embodiments of the inventions are illustrated in the figures. However, the embodiments and figures are illustrative rather than limiting; they provide examples of the invention. 
           [0012]      FIG. 1  depicts an example of a system for validating a client at a server. 
           [0013]      FIG. 2  depicts a flowchart of an example of a method for power up and power down of a device appropriate for use in the system. 
           [0014]      FIG. 3  depicts a flowchart of an example of a method for generating a device certificate only once. 
           [0015]      FIG. 4  depicts a computer system suitable for implementation of the techniques described above with reference to  FIGS. 1-3 . 
           [0016]      FIG. 5  depicts an example of a secure system suitable for implementation of the techniques described above with reference to  FIGS. 1-3 . 
           [0017]      FIG. 6  depicts a flowchart of an example of a method for manufacturing a secure device. 
           [0018]      FIG. 7  depicts a flowchart of an example of a method for construction of a secure certificate. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    In the following description, several specific details are presented to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or in combination with other components, etc. In other instances, well-known implementations or operations are not shown or described in detail to avoid obscuring aspects of various embodiments, of the invention. 
         [0020]      FIG. 1  depicts an example of a system  100  for validating a client at a server. In the example of  FIG. 1 , the system  100  includes a server  102 , a network  104 , and a client  106 . The server  102  includes a certificate request module  110 , a certificate verification module  112 , a Cert database  114 , a pseudo-random number (PRN) generator  116 , and an interface  118 . The client  106  includes a certificate generation module  120 , non-volatile (NV) memory  122 , and an interface  124 . 
         [0021]    The server  102  may be any applicable known or convenient computer. The network  104  may be any communications network including, by way of example but not limitation, the Internet. The client  106  may be any applicable known or convenient computer that has secure storage. The NV memory  122  may include a secure key store and, in an embodiment, the NV memory  122  is on-chip memory. 
         [0022]    In the example of  FIG. 1 , in operation, a protocol for registration or activation is initiated by the server  102 . (The client  106  may, in an alternative, initiate the registration or activation.) In an embodiment, the protocol serves to register a device identity and certificate into the cert database  114 . To do so, the PRN generator  116  generates a PRN, R, and the certificate request module  110  of the server  102  generates a request for a device certificate. R and the request for a device certificate are sent via the interface  118  to the network  104 . 
         [0023]    R and the request for a device certificate are received at the interface  124  of the client  106 . The certificate generation module  120  of the client  106  generates a certificate Cert. An example of the algorithm used to generate Cert is described with reference to  FIG. 7 , below. The certificate generation module  120  computes a signature Sig, over random number R, using a device private key. Operands are stored in the NV memory  122 , which may reside in, for example, a secure kernel (see e.g.,  FIG. 5 ). In an alternative, the computation could include a device ID, serial number, region code, or some other value. The interface  124  of the client  106  returns R, any optional data, Cert, and Sig to the network  104 . 
         [0024]    The interface  118  receives at the server  102  R, any optional data, Cert, and Sig. The certificate verification module  112  at the server  102  validates Cert using a trusted certificate chain, validates Sig using Cert, and verifies that R is the same as the value, R, that was originally sent by the server  102  to the client  106 . If successfully validated and verified, the server  102  imports Cert into the Cert database  116 . At this point, the client  106  is presumably authorized to obtain from the server  102 —or some other location that can use the certificate to authorize the client  106 —digital licenses for rights managed content, and other operations. 
         [0025]    In another embodiment, the device could generate a new key pair {pvt 1 ,pub 1 } using a RNG, and a certificate could be created for the new public key pub 1 , using the device programmed private key as signer. This new key pvt 1  could be used to sign the message having the random R. 
         [0026]    It should be noted that secure networking protocols such as SSL and other services that require ephemeral secret keys typically make use of a source of a string of random numbers. A secure manufacturing process, such as is described by way of example but not limitation with reference to  FIG. 6 , below, can be used to seed a secret random number S in a device. A PRN generating algorithm using cryptographic primitives such as the functions in AES or SHA can be used to generate PRNs. The sequence should not repeat after power-cycle of the device. Using a state-saving mechanism involving the chip non-volatile memory ensures a high level of security. The device uses a part of re-writeable non-volatile memory to store a sequence number. 
         [0027]      FIG. 2  depicts a flowchart  200  of an example of a method for power up and power down of a device appropriate for use in the system  100 . In the example of  FIG. 2 , the flowchart  200  starts at module  202  where a device is powered on. In the example of  FIG. 2 , the flowchart  200  continues to module  204  where runtime state is initialized to 1. Since the runtime state is incremented over time, the runtime state should be stored in writable memory, such as on-chip writable memory. 
         [0028]    In the example of  FIG. 2 , the flowchart  200  continues to module  206  where the device increments the sequence number and computes key=fn(S, sequence number), where S=a programmed secret seed random number. Since S is programmed, it can be stored in on-chip NV read-only memory (ROM). At this point, the device is presumed to be “up and running.” 
         [0029]    In the example of  FIG. 2 , the flowchart  200  continues to module  208  where, in response to a request for a random number, the device generates random=fn(key, state) and increments state: state++. In the example of  FIG. 2 , the flowchart  200  continues to decision point  210  where it is determined whether another random number request is received. If it is determined that another random number request has been received ( 210 -Y), then the flowchart  200  returns to module  208 . In this way, module  208  may be repeated multiple times for multiple random number requests. 
         [0030]    When it is determined there are no other random number requests ( 210 -N), the flowchart  200  continues to module  212  where the device is powered off, and the state is lost. Thus, the flowchart  200  illustrates the state of the device from power on to power off. If the device is powered on again, a new key must be computed, and state initialized again. 
         [0031]      FIG. 3  depicts a flowchart  300  of an example of a method for generating a device certificate only once. In the example of  FIG. 3 , the flowchart  300  starts at module  302  where a device certificate is generated at a secure device. The flowchart  300  continues to module  304  where the device certificate is stored in system external storage. This variation is notable because the device is secure, but the device certificate is public. Accordingly, the certificate is still secure, even though it is not regenerated each time. 
         [0032]      FIG. 4  depicts a computer system  400  suitable for implementation of the techniques described above with reference to  FIGS. 1-3 . The computer system  400  includes a computer  402 , I/O devices  404 , and a display device  406 . The computer  402  includes a processor  408 , a communications interface  410 , memory  412 , display controller  414 , non-volatile storage  416 , and I/O controller  418 . The computer  402  may be coupled to or include the I/O devices  404  and display device  406 . 
         [0033]    The computer  402  interfaces to external systems through the communications interface  410 , which may include a modem or network interface. The communications interface  410  can be considered to be part of the computer system  400  or a part of the computer  402 . The communications interface  410  can be an analog modem, ISDN modem, cable modem, token ring interface, satellite transmission interface (e.g. “direct PC”), or other interfaces for coupling a computer system to other computer systems. Although conventional computers typically include a communications interface of some type, it is possible to create a computer that does not include one, thereby making the communications interface  410  optional in the strictest sense of the word. 
         [0034]    The processor  408  may include, by way of example but not limitation, a conventional microprocessor such as an Intel Pentium microprocessor or Motorola power PC microprocessor. While the processor  408  is a critical component of all conventional computers, any applicable known or convenient processor could be used for the purposes of implementing the techniques described herein. The memory  412  is coupled to the processor  408  by a bus  420 . The memory  412 , which may be referred to as “primary memory,” can include Dynamic Random Access Memory (DRAM) and can also include Static RAM (SRAM). The bus  220  couples the processor  408  to the memory  412 , and also to the non-volatile storage  416 , to the display controller  414 , and to the I/O controller  418 . 
         [0035]    The I/O devices  404  can include a keyboard, disk drives, printers, a scanner, and other input and output devices, including a mouse or other pointing device. For illustrative purposes, at least one of the I/O devices is assumed to be a block-based media device, such as a DVD player. The display controller  414  may control, in a known or convenient manner, a display on the display device  406 , which can be, for example, a cathode ray tube (CRT) or liquid crystal display (LCD). 
         [0036]    The display controller  414  and I/O controller  418  may include device drivers. A device driver is a specific type of computer software developed to allow interaction with hardware devices. Typically this constitutes an interface for communicating with the device, through a bus or communications subsystem that the hardware is connected to, providing commands to and/or receiving data from the device, and on the other end, the requisite interfaces to the OS and software applications. 
         [0037]    The device driver may include a hardware-dependent computer program that is also OS-specific. The computer program enables another program, typically an OS or applications software package or computer program running under the OS kernel, to interact transparently with a hardware device, and usually provides the requisite interrupt handling necessary for any necessary asynchronous time-dependent hardware interfacing needs. 
         [0038]    The non-volatile storage  416 , which may be referred to as “secondary memory,” is often a magnetic hard disk, an optical disk, or another form of storage for large amounts of data. Some of this data is often written, by a direct memory access process, into memory  412  during execution of software in the computer  402 . The non-volatile storage  416  may include a block-based media device. The terms “machine-readable medium” or “computer-readable medium” include any known or convenient storage device that is accessible by the processor  408  and also encompasses a carrier wave that encodes a data signal. 
         [0039]    The computer system  400  is one example of many possible computer systems which have different architectures. For example, personal computers based on an Intel microprocessor often have multiple buses, one of which can be an I/O bus for the peripherals and one that directly connects the processor  408  and the memory  412  (often referred to as a memory bus). The buses are connected together through bridge components that perform any necessary translation due to differing bus protocols. 
         [0040]    Network computers are another type of computer system that can be used in conjunction with the teachings provided herein. Network computers do not usually include a hard disk or other mass storage, and the executable programs are loaded from a network connection into the memory  412  for execution by the processor  408 . A Web TV system, which is known in the art, is also considered to be a computer system, but it may lack some of the features shown in  FIG. 4 , such as certain input or output devices. A typical computer system will usually include at least a processor, memory, and a bus coupling the memory to the processor. 
         [0041]    The computer system  400  may be controlled by an operating system (OS). An OS is a software program—used on most, but not all, computer systems—that manages the hardware and software resources of a computer. Typically, the OS performs basic tasks such as controlling and allocating memory, prioritizing system requests, controlling input and output devices, facilitating networking, and managing files. Examples of operating systems for personal computers include Microsoft Windows®, Linux, and Mac OS®. Delineating between the OS and application software is sometimes rather difficult. Fortunately, delineation is not necessary to understand the techniques described herein, since any reasonable delineation should suffice. 
         [0042]    The lowest level of an OS may be its kernel. The kernel is typically the first layer of software loaded into memory when a system boots or starts up. The kernel provides access to various common core services to other system and application programs. 
         [0043]    As used herein, algorithmic descriptions and symbolic representations of operations on data bits within a computer memory are believed to most effectively convey the techniques to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of operations leading to a desired result. The operations are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. 
         [0044]    It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussion, it is appreciated that throughout the description, discussions utilizing terms such as “processing” or “computing” or “calculating” or “determining” or “displaying” or the like, refer to the action and processes of a computer that manipulates and transforms data represented as physical (electronic) quantities within the computer system&#39;s registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. 
         [0045]    An apparatus for performing techniques described herein may be specially constructed for the required purposes, or it may comprise a general purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer readable storage medium, such as, by way of example but not limitation, read-only memories (ROMs), RAMs, EPROMs, EEPROMs, magnetic or optical cards, any type of disk including floppy disks, optical disks, CD-ROMs, DVDs, and magnetic-optical disks, or any known or convenient type of media suitable for storing electronic instructions. 
         [0046]    The algorithms and displays presented herein are not inherently related to any particular computer architecture. The techniques may be implemented using any known or convenient programming language, whether high level (e.g., C/C++) or low level (e.g., assembly language), and whether interpreted (e.g., Perl), compiled (e.g., C/C++), or Just-In-Time (JIT) compiled from bytecode (e.g., Java). Any known or convenient computer, regardless of architecture, should be capable of executing machine code compiled or otherwise assembled from any language into machine code that is compatible with the computer&#39;s architecture. 
         [0047]      FIG. 5  depicts an example of a secure system  500  suitable for implementation of the techniques described above with reference to  FIGS. 1-3 . A typical secure system  500  may include a game console, media player, an embedded secure device, a “conventional” PC with a secure processor, or some other computer system that includes a secure processor. 
         [0048]    In the example of  FIG. 5 , the secure system  500  includes a secure processor  502 , an OS  504 , ticket services  506 , a calling application  508 , and protected memory  510 . In the example of  FIG. 5 , the OS  504  includes a security kernel  514 , which in turn includes a key store  516 , an encryption/decryption engine  517 , and a security API  518 . It should be noted that one or more of the described components, or portions thereof, may reside in the protected memory  510 , or in unprotected memory (not shown). 
         [0049]    It should further be noted that the security kernel  514  is depicted as residing inside the OS  504  by convention only. It may or may not actually be part of the OS  504 , and could exist outside of an OS or on a system that does not include an OS. For the purposes of illustrative simplicity, it is assumed that the OS  504  is capable of authentication. In an embodiment, the ticket services  506  may also be part of the OS  504 . This may be desirable because loading the ticket services  506  with authentication can improve security. Thus, in such an embodiment, the OS  504  is loaded with authentication and includes the ticket services  506 . 
         [0050]    For illustrative simplicity, protected memory is represented as a single memory. However protected memory may include protected primary memory, protected secondary memory, and/or secret memory. It is assumed that known or convenient mechanisms are in place to ensure that memory is protected. The interplay between primary and secondary memory and/or volatile and non-volatile storage is known so a distinction between the various types of memory and storage is not drawn with reference to  FIG. 5 . 
         [0051]    The ticket services  506  may be thought of as, for example, “digital license validation services” and, in a non-limiting embodiment, may include known or convenient procedures associated with license validation. For example, the ticket services  506  may include procedures for validating digital licenses, PKI validation procedures, etc. In the example of  FIG. 5 , the ticket services  506  can validate a ticket from the calling application  508 . In operation, the ticket services  506  obtains the ticket from the calling application  508 , which proceeds to validate the ticket. 
         [0052]    It is possible that the ticket is personalized. In that case, it could be decrypted using the device private key (programmed as discussed before) to compute a secret shared encryption key. The ticket may or may not be obtained using an Internet download mechanism and stored on re-writable flash memory. 
         [0053]    In an embodiment, the security kernel  514  may be loaded at start-up. In another embodiment, a portion of the security kernel may be loaded at start-up, and the remainder loaded later. An example of this technique is described in application Ser. No. 10/360,827 entitled “Secure and Backward-Compatible Processor and Secure Software Execution Thereon,” which was filed on Feb. 7, 2003, by Srinivasan et al., and which is incorporated by reference. Any known or convenient technique may be used to load the security kernel  514  in a secure manner. 
         [0054]    The key store  516  is a set of storage locations for keys. The key store  516  may be thought of as an array of keys, though the data structure used to store the keys is not critical. Any applicable known or convenient structure may be used to store the keys. In a non-limiting embodiment, the key store  516  is initialized with static keys, but variable keys are not initialized (or are initialized to a value that is not secure). For example, some of the key store locations are pre-filled with trusted values (e.g., a trusted root key) as part of the authenticated loading of the security kernel  514 . The private key in the non-volatile memory could be retrieved and stored in the keystore for future use. 
         [0055]    The encryption/decryption engine  517  is, in an embodiment, capable of both encryption and decryption. For example, in operation, an application may request of the security API  518  a key handle that the application can use for encryption. The encryption/decryption engine  517  may be used to encrypt data using the key handle. Advantageously, although the security API  518  provides the key handle in the clear, the key itself never leaves the security kernel  514 . 
         [0056]    The security API  518  is capable of performing operations using the keys in the key store  516  without bringing the keys out into the clear (i.e., the keys do not leave the security kernel  514  or the keys leave the security kernel  514  only when encrypted). The security API  518  may include services to create, populate and use keys (and potentially other security material) in the key store  516 . In an embodiment, the security API  518  also provides access to internal secrets and non-volatile data, including secret keys and device private key. For example, the device private key might be stored in the keystore and used by the security API. One API call could be used to return a device certificate (using an algorithm discussed herein to generate the certificate). Another API call can be constructed to use the private key to compute a shared key for decryption, or use the private key to sign a message or certificate. Depending upon the implementation, the security API  518  may support AES and SHA operations using hardware acceleration. 
         [0057]    In the example of  FIG. 5 , the ticket services  506  and the security API  518  may execute in a separate execution space for system security. In order to validate data blocks, the ticket services  506  may validate the ticket using data in the header. The ticket may include an encrypted key. The ticket services  506  decrypts the key using services in the security kernel  514  (e.g., the encryption/decryption engine  517 ). 
         [0058]    In an embodiment, the encryption/decryption engine  517  uses secret common keys from the key store  518  to perform this decryption. In another embodiment, the ticket services  506  could use a device personalized ticket obtained from flash or network (not shown), validate some rights to content, and then return the key. In any case, this process returns the key. The personalized ticket could be encrypted by a key that is a function of the device private key, programmed in the non-volatile memory. 
         [0059]    An example of data flow in the system  500  is provided for illustrative purposes as arrows  520 - 528 . Receiving the certificate request at the ticket services  506  is represented by a certificate request arrow  520  from the calling application  508  to the ticket services  506 . 
         [0060]    Forwarding the certificate request from the ticket services  506  to the security API  516  is represented by a certificate request arrow  522 . Within the security kernel  514 , the public key/device certificate construction engine  517  accesses keys/signature data from the key/signature store  518 . The access is represented by the private key/signature access arrow  524 . The security API  516  returns a device certificate to the ticket services  506 , as represented by the device certificate arrow  526 , which is forwarded to the calling application  508 , as represented by the device certificate arrow  528 . 
         [0061]      FIG. 6  depicts a flowchart  600  of an example of a method for manufacturing a secure device. This method and other methods are depicted as serially arranged modules. However, modules of the methods may be reordered, or arranged for parallel execution as appropriate. In the example of  FIG. 6 , the flowchart  600  begins at module  602  where a device ID is obtained. The device ID may be a serial number or some other unique identifier for the device. 
         [0062]    In the example of  FIG. 6 , the flowchart  600  continues to module  604  where a pseudo-random number is provided for use as a small-signature private key for the device. To date, truly random numbers are not generable on a computer; of course, a pseudo-random number generator or an external secured hardware true random number generator could work for the intended purpose. A small-signature private key may be, by way of example but not limitation, an elliptic curve private key, or some other private key with a relatively small footprint. 
         [0063]    In the example of  FIG. 6 , the flowchart  600  continues to module  606  where a public key is computed from the private key using common parameters. For example, a multiple of a base point may be computed, where a scalar multiple is the private key. 
         [0064]    In the example of  FIG. 6 , the flowchart  600  continues to module  608  where a fixed certificate structure is used to construct a certificate. The certificate is signed using a small signature algorithm such as elliptic curve DSA. In an embodiment, the fixed certificate structure may include at least the device ID, issuer name, and device public key. A small-signature algorithm is used to minimize the size of the signature. By way of example but not limitation, an elliptic curve signature algorithm may be used. 
         [0065]    In the example of  FIG. 6 , the flowchart  600  continues to module  610  where {device ID, private key, issuer ID, signature} is programmed into the non-volatile memory of the device. This set includes these four items because the items provide sufficient security for most purposes, and the set has a relatively small footprint due to the relatively small size of the private key and signature. (The device ID and issuer ID also, presumably, have relatively small footprints.) In an embodiment, any other data that is needed to construct the device certificate such as the public key may be generated programmatically on demand. However, more items could be programmed into the non-volatile memory, or fewer, as appropriate for a given embodiment or implementation. 
         [0066]    In the example of  FIG. 6 , the flowchart  600  continues to module  612  where a secret random number is programmed into the ROM of the device. The secret random number may be pseudo-randomly generated or arbitrarily assigned. This secret random number can be used to support secure pseudo-random number generation. In an alternative, the ROM may be replaced with some other known or convenient NV storage. 
         [0067]      FIG. 7  depicts a flowchart  700  of an example of a method for construction of a secure certificate. Advantageously, the method enables the device having the non-volatile programmed key and required software to construct a full device certificate that can be used to validate the device. In the example of  FIG. 7 , the flowchart  700  starts at module  702  where a request for a device certificate is received from a calling application. 
         [0068]    In the example of  FIG. 7 , the flowchart  700  continues to module  704  where {device ID, private key, issuer ID, signature} is read from non-volatile memory. In an embodiment, a security kernel module accesses and reads the non-volatile memory. An example of a security kernel module that is appropriate for this purpose is described in U.S. patent application Ser. No. 10/360,827 entitled “Secure and Backward-Compatible Processor and Secure Software Execution Thereon,” which was filed on Feb. 7, 2003, by Srinivasan et al., and/or in U.S. patent application Ser. No. 11/586,446 entitled “Secure Device Authentication System and Method,” which was filed on Oct. 24, 2006, by Srinivasan et al., both of which are incorporated by reference. However, any applicable known or convenient security kernel module could be used. 
         [0069]    In the example of  FIG. 7 , the flowchart  700  continues to module  706  where the public key is computed from the private key and common parameters, if any. In an embodiment, the computation makes use of the same algorithm that was used in a manufacturing process, such as the method described with reference to  FIG. 6 , above. The public key may be computed in a security kernel. 
         [0070]    In the example of  FIG. 7 , the flowchart  700  continues to module  708  where a device certificate is constructed from device ID, issuer ID, public key, signature, and common parameters. In an embodiment, a security kernel module is aware of the structure of the device certificate, as is used in a manufacturing process, such as the method described with reference to  FIG. 6 , above. Advantageously, the device certificate can be constructed on demand. 
         [0071]    In the example of  FIG. 7 , the flowchart  700  continues to module  710  where the device certificate is provided to the calling application. The flowchart  700  ends when the device certificate is provided to the calling application. The method could be started again by another calling application (or by the same calling application if, for some reason, the device certificate was needed again.) 
         [0072]    As used herein, the term “content” is intended to broadly include any data that can be stored in memory. 
         [0073]    As used herein, the term “embodiment” means an embodiment that serves to illustrate by way of example but not limitation. 
         [0074]    It will be appreciated to those skilled in the art that the preceding examples and embodiments are exemplary and not limiting to the scope of the present invention. It is intended that all permutations, enhancements, equivalents, and improvements thereto that are apparent to those skilled in the art upon a reading of the specification and a study of the drawings are included within the true spirit and scope of the present invention. It is therefore intended that the following appended claims include all such modifications, permutations and equivalents as fall within the true spirit and scope of the present invention.