Patent Publication Number: US-RE38375-E

Title: Method and system for the secured distribution of multimedia titles

Description:
This is a continuation of application Ser. No. 08/354,700, filed Dec. 13, 1994, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention generally relates to an improved data processing system, and in particular to a method and system for distributing multimedia programs. Still more particularly, the present invention relates to a method and system for checking for authorized multimedia programs and detecting unauthorized multimedia programs in a data processing system. 
     2. Description of the Related Art 
     Multimedia data processing systems present information in data to a user utilizing sound, graphics, animation, and text. Programs presenting data and information to a user in this form are also called multimedia titles. Typically, a software company develops and markets a software system for the production and presentation of multimedia titles. Such a software system is used in composing multimedia scripts for multimedia titles. Typically, the software system includes a set of authoring tools for producing multimedia titles by developers and a Run Time Environment (RTE) for presenting the multimedia titles to end users. Typically, the RTE is designed to execute on various computing platforms, which makes the authoring tools for the software system desirable to developers. Typically, developers pay a royalty to the software company for using the authoring tools to develop multimedia titles to run on the RTE. But some unscrupulous developers may produce unauthorized titles and avoid royalty payments in producing multimedia titles for use on the RTE. Therefore, it would be advantageous to have a method and system to allow authorized titles to execute on a data processing system and to detect attempted execution of unauthorized titles. 
     SUMMARY OF THE INVENTION 
     It is one object of the present invention to provide an improved data processing system. 
     It is another object of the present invention to provide a method and system for distributing multimedia programs. 
     It is yet another object of the present invention to provide a method and system for checking for authorized multimedia programs and detecting unauthorized multimedia programs in a data processing system. 
     The present invention provides a method and system for detecting authorized multimedia programs within a data processing system. The present invention creates a validation structure for validating a multimedia program. The validation structure is embedded in the multimedia program and in response to an initiation of the multimedia program, a determination is made as to whether the multimedia program is an authorized multimedia program. The determination is made using the validation structure. 
     In creating the validation structure, sections of the program (hereinafter called data objects) are selected and a cryptographic hash value is created or calculated on each of the selected data objects. The cryptographic hash value and the location of the selected data object are stored as a data record within the validation structure. In addition, a signature is included or associated with the validation structure. The signature is calculated on the validation structure using a public key cryptographic algorithm in accordance with a preferred embodiment of the present invention. 
     Determining whether a multimedia program is an authorized multimedia program is accomplished by selecting a subset of the data objects within the multimedia program and validating the selected data objects using the validation structure stored in the multimedia program. This includes the steps of randomly selecting a portion of the data objects from among a defined set of data records listed in the validation structure, reading the selected data objects from the multimedia program using location information stored in the validation structure, and validating the selected data objects using validation information stored in the validation structure. For each selected data object, the location information stored in the validation structure is accessed and used to read the selected data object from the multimedia program. A cryptographic hash value is calculated on the selected data object and then compared for equality with a corresponding hash-value-of-reference stored in the validation structure The hash values must be equal for the selected data objects to be valid. In addition, the validation structure is itself validated through the use of the signature previously calculated on the validation structure, using a public key cryptographic algorithm, and stored with the validation structure. If the signature, validation structure, and subset of selected data objects are valid, the multimedia program is considered to be an authorized multimedia program. An authorized multimedia program is allowed to execute normally, otherwise, execution of the multimedia program may be prohibited or limited execution of the multimedia program may be allowed in response to a determination that the multimedia program is not an authorized program. 
     The above as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
     FIG. 1 depicts a data processing system in the form of a personal computer in which the present invention can be employed; 
     FIG. 2 is a block diagram of a personal computer system illustrating the various components of personal computer system in accordance with the present invention; 
     FIG. 3 is a block diagram of a creation and distribution process for multimedia titles on CD-ROM depicted in accordance with a preferred embodiment of the present invention. 
     FIG. 4 is a depiction of entries in a table of contents in accordance with a preferred embodiment of the present invention; 
     FIG. 5 is a block diagram of a signature token generation module, depicted in accordance with a preferred embodiment of the present invention; 
     FIG. 6 is a block diagram of a signature token validation module depicted in accordance with a preferred embodiment of the present invention; 
     FIG. 7 is a flowchart of a process for generating signature tokens in a signature token generation module depicted in accordance with a preferred embodiment of the present invention; and 
     FIG. 8 is a flowchart of a process for validating multimedia titles in a validation program depicted in accordance with a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     With reference now to the figures and in particular with reference to FIG. 1, a data processing system, personal computer system  10  is depicted, in which the present invention can be employed. As shown, personal computer system  10  comprises a number of components, which are interconnected together. More particularly, a system unit  12  is coupled to and can drive an optional monitor  14  (such as a conventional video display). A system unit  12  also can be optionally coupled to input devices such as a PC keyboard  16  or a mouse  18 . Mouse  18  includes right and left buttons (not shown). The left button is generally employed as the main selector button and alternatively is referred to as the first mouse button or mouse button  1 . The right button is typically employed to select auxiliary functions as explained later. The right mouse button is alternatively referred to as the second mouse button or mouse button  2 . An optional output device, such as a printer  20 , also can be connected to the system unit  12 . Finally, system unit  12  may include one or more mass storage devices such as the diskette drive  22 . 
     As will be described below, the system unit  12  responds to input devices, such as PC keyboard  16 , the mouse  18 , or local area networking interfaces. Additionally, input/output (I/O) devices, such as floppy diskette drive  22 , display  14 , printer  20 , and local area network communication system are connected to system unit  12  in a manner well known. Of course, those skilled in the art are aware that other conventional components also can be connected to the system unit  12  for interaction therewith. In accordance with the present invention, personal computer system  10  includes a system processor that is interconnected to a random access memory (RAM), a ready only memory (ROM), and a plurality of I/O devices. 
     In normal use, personal computer system  10  can be designed to give independent computing power to a small group of users as a server or a single user and is inexpensively priced for purchase by individuals or small businesses. In operation, the system processor functions under an operating system, such as IBM&#39;s OS/2 operating system or DOS. OS/2 is a registered trademark of International Business Machines Corporation. This type of operating system includes a Basic Input/Output System (BIOS) interface between the I/O devices and the operating system. BIOS, which can be stored in a ROM on a motherboard or planar, includes diagnostic routines which are contained in a power on self test section referred to as POST. 
     Prior to relating the above structure to the present invention, a summary of the operation in general of personal computer system  10  may merit review. Referring to FIG. 2, there is shown a block diagram of personal computer system  10  illustrating the various components of personal computer system  10  in accordance with the present invention. FIG. 2 further illustrates components of planar  11  and the connection of planar  11  to I/O slots  46 a- 46 d and other hardware of personal computer system  10 . Connected to planar  11  is the system central processing unit (CPU)  26  comprised of a microprocessor which is connected by a high speed CPU local bus  24  through a bus controlled timing unit  38  to a memory control unit  50  which is further connected to a volatile random access memory (RAM)  58 . While any appropriate microprocessor can be used for CPU  26 , one suitable microprocessor is the Pentium microprocessor, which is sold by Intel Corporation. “Pentium” is a trademark of Intel Corporation. 
     While the present invention is described hereinafter with particular reference to the system block diagram of FIG. 2, it is to be understood at the outset of the description which follows, it is contemplated that the apparatus and methods in accordance with the present invention may be used with other hardware configurations of the planar board. For example, the system processor could be an Intel 80286, 80386, or 80486 microprocessor. These particular microprocessors can operate in a real addressing mode or a protected addressing mode. Each mode provides an addressing scheme for accessing different areas of the microprocessor&#39;s memory. 
     Returning now to FIG. 2, CPU local bus  24  (comprising data, address and control components) provides for the connection of CPU  26 , an optional math coprocessor  27 , a cache controller  28 , and a cache memory  30 . Also coupled on CPU local bus  24  is a buffer  32 . Buffer  32  is itself connected to a slower speed (compared to the CPU local bus) system bus  34 , also comprising address, data and control components. System bus  34  extends between buffer  32  and a further buffer  36 . System bus  34  is further connected to a bus control and timing unit  38  and a Direct Memory Access (DMA) unit  40 . DMA unit  40  is comprised of a central arbitration unit  48  and a DMA controller  41 . Buffer  36  provides an interface between the system bus  34  and an optional feature bus such as the Micro Channel bus  44 . “Micro Channel” is a registered trademark of International Business Machines Corporation. Connected to bus  44  are a plurality of I/O slots  46 a- 46 d for receiving Micro Channel adapter cards which may be further connected to an I/O device or memory. In the depicted example, I/O slot  46 c has a hard disk drive connected to it; I/O slot  46 b has a CD-ROM drive connected to it; and I/O slot  46 a has a ROM on an adapter card connected to it. Other devices, such as a modem may be connected to an I/O slot. An arbitration control bus  42  couples the DMA controller  41  and central arbitration unit  48  to I/O slots  46  and diskette adapter  82 . Also connected to system bus  34  is a memory control unit  50  which is comprised of a memory controller  52 , an address multiplexer  54 , and a data buffer  56 . Memory control unit  50  is further connected to a random access memory as represented by RAM module  58 . Memory controller  52  includes the logic for mapping addresses to and from CPU  26  to particular areas of RAM  58 . While the personal computer system  10  is shown with a basic 1 megabyte RAM module in RAM  58 , it is understood that additional memory can be interconnected as represented in FIG. 2 by the optional memory modules  60  through  64 . 
     A further buffer  66  is coupled between system bus  34  and a planar I/O bus  68 . Planar I/O bus  68  includes address, data, and control components respectively. Coupled along planar bus  68  are a variety of I/O adapters and other peripheral components such as display adapter  70  (which is used to drive an optional display  14  depicted in FIG.  1 ), a clock  72 , nonvolatile RAM  74  (hereinafter referred to as “NVRAM”), a RS232 adapter  76 , a parallel adapter  78 , a plurality of timers  80 , a diskette adapter  82 , a PC keyboard/mouse controller  84 , and a read only memory (ROM)  86 . The ROM  86  includes BIOS which provides the user transparent communications between many I/O devices. 
     Clock  72  is used for time of day calculations. NVRAM  74  is used to store system configuration data. That is, the NVRAM will contain values which describe the present configuration of the system. For example, NVRAM  74  contains information which describe the capacity of a fixed disk or diskette, the type of display, the amount of memory, etc. Of particular importance, NVRAM  74  will contain data which is used to describe the system console configuration; i.e., whether a PC keyboard is connected to the keyboard/mouse controller  84 , a display controller is available or the ASCII terminal is connected to RS232 adapter  76 . Furthermore, these data are stored in NVRAM  74  whenever a special configuration program is executed. The purpose of the configuration program is to store values characterizing the configuration of this system to NVRAM  76  which are saved when power is removed from the system. 
     Connected to keyboard/mouse controller  84  are ports A and B. These ports are used to connect a PC keyboard (as opposed to an ASCII terminal) and mouse to the PC system. Coupled to RS232 adapter unit  76  is an RS232 connector. An optional ASCII terminal can be coupled to the system through this connector. 
     Specifically, personal computer system  10  may be implemented utilizing any suitable computer such as the IBM PS/2 computer or an IBM RISC SYSTEM/6000 computer, both products of International Business Machines Corporation, located in Armonk, N.Y. “RISC SYSTEM/6000” is a trademark of International Business Machines Corporation and “PS/2” is a registered trademark of International Business Machines Corporation. 
     Distribution of multimedia programs or titles (hereinafter called “multimedia titles”) involves an application developer who produces multimedia titles using an authoring tool and a Run Time Environment (RTE) provided by a multimedia company and a user who purchases multimedia titles for execution on a computer or computer platform executing the RTE. In accordance with a preferred embodiment of the present invention, checking for authorized multimedia titles and detecting unauthorized multimedia titles involves a scheme of digital signatures using a public key algorithm. A “public key” is a key made available to anyone who wants to encrypt information. In public key cryptography, public key algorithms are used in which a public key is used for encryption and a private key is used for decryption. The basis for public key cryptography includes discrete logarithms, factoring, and the knapsack problem. Each authorized multimedia title includes an embedded digital signature token that can be verified by the RTE before the multimedia title is permitted to execute on the data processing system. 
     Two cryptographic subsystems are employed to facilitate the signature token generation and signature token verification processes in accordance with a preferred embodiment of the present invention. One cryptographic subsystem enables the generation of signature tokens that, when embedded in authorized multimedia titles, will permit these titles to be validated. Another cryptographic subsystem is employed to validate the signature tokens. In this manner authorized multimedia titles may be distinguished from unauthorized multimedia titles. 
     With reference to FIG. 3, a block diagram of a creation and distribution process for multimedia titles on CD-ROM is depicted in accordance with a preferred embodiment of the present invention. Those skilled in the art will recognize that the subject invention could be practiced in an implementation wherein multimedia titles are distributed on media other than a CD ROM medium. A multimedia title is developed by a developer using authoring tool  300 . The multimedia title is then processed using signature token generation model  302 . This module generates a signature token for the multimedia title. The signature token is embedded within the multimedia title. Thereafter, the multimedia title with the signature token embedded within it is sent back to the developer who creates a master CD-ROM  304 . Alternatively, the signature token and multimedia title are sent back to the developer, whereupon the signature token is embedded into the multimedia title and a master CD-ROM  304  is created by the developer. From master CD-ROM  304 , CD-ROM  306  is produced containing the multimedia title and the embedded signature token. CD-ROM  306  may be placed within data processing system  308 , which includes the RTE with the signature token validation module in accordance with a preferred embodiment of the present invention. When the title is to be executed within data processing system  308 , the RTE reads the signature token from the CD-ROM and validates the signature token and a selected portion of the data objects also read from the CD-ROM using the signature token validation module. 
     Typically, a multimedia title takes about one hour to play and contains about 650 megabytes of data. As a result, it is inefficient to validate a multimedia title by reading and checking each byte within the title. In accordance with a preferred embodiment of the present invention, the multimedia title is validated by checking a portion of the data contained therein. 
     Random sampling of data to validate multimedia titles is employed in accordance with a preferred embodiment of the present invention. If the data locations to be sampled were constant from one instance of validation to the next, then only a small portion of the multimedia title would be checked. In such a situation, forged titles could be more easily constructed. But by randomly selecting data locations for sampling, the possibility of forged multimedia titles is greatly reduced. 
     In addition, the presently claimed invention utilizes data context sampling. A significant improvement in the validation of multimedia titles may be achieved if the logical structure of the multimedia titles themselves is employed to identify key pieces of data to be validated. For example, a preferred checking strategy may be based on checking part or all of the data in the table of contents for each file in a multimedia title. A multimedia title consists of one or more files, each containing its own table of contents. In many cases the multimedia title contains only one such file. When a file is opened, the table of contents is the first item to be read. 
     With reference now to FIG. 4, a depiction of entries in a table of contents is illustrated in accordance with a preferred embodiment of the present invention. Table of contents  400  includes entries  402 - 408 . Each entry includes an object identifier, a property identifier, a type, and a location (offset and length). As a result, a particular entry indicates that at a particular offset on the disk, for this many bytes, a property with this ID belonging to an object with this ID of this type is located. Because the table of contents references data on the basis of an Object ID and a Property ID, the referenced data object is said to be referenced by an object-property (OP) pair and the data object is referred to as OP data. Of course, other formats and specifications for the table of contents may be utilized in accordance with a preferred embodiment of the present invention. The table of contents, regardless of its format, structure, and sematics, may be employed to effectively validate a multimedia title in accordance with a preferred embodiment of the present invention. Typically in multimedia titles, the table of contents is an example of a relatively short and easily identifiable piece of information that has an intrinsic dependency with most of the other parts of the multimedia title. The table of contents could take the form of a symbol table, a linkage map, and so forth, but is rigidly specified and highly structured. 
     Furthermore, for multimedia titles, the first few displayed screens typically contain the name of the title and its version. As a result, protecting these screens is desirable. Therefore, a checking strategy may include checking the first few screens of data displayed to a user so that a forged title, whose name is for example “Demons for the Deep”, would be forced to display the name of the title upon which it is piggy-backing, say “Desert Wargames”. 
     The present invention provides a method and system for validating multimedia titles by validating part or all of the table of contents and the first few displayed screens containing the name of the title and its version for each multimedia file and validating a subset of the data objects in the multimedia title. These data objects are selected randomly in accordance with a preferred embodiment of the present invention. But those skilled in the art will recognize that the data objects could be selected using a preferred method which is non-random, without departing from the spirit of the present invention. 
     With reference to FIG. 5, a diagram of a signature token is depicted in accordance with a preferred embodiment of the present invention. Signature token  500  is constructed by a signature token generation module (not shown in FIG.  5 ). The signature token is constructed step-by-step by making repeated service requests to the signature token generation module. Once created, signature token  500  is embedded in the multimedia title upon which it was generated. This signature token is validated by a signature token validation module in the RTE. In validation, the signature token is validated step-by-step by making repeated service requests to the signature token validation module. 
     Signature token  500  includes a header  502  and data records 1 through n that correspond to data or data objects in the multimedia title that can be selected and validated. The data records 1 through n in the signature token are different from the data objects in the multimedia title, although there is a direct correspondence. In addition, signature token  500  includes digital signature  504 , which is employed to validate the header and the series of data records 1 through n in the signature token. Each data record within signature token  500  includes location specific information, L, and a cryptographic hash value, H. Location specific information tells the signature token validation module the location or locations in the multimedia title of the data to be validated. The hash value is calculated on the specific multimedia data referenced by L. In accordance with a preferred embodiment of the present invention, the cryptographic hash value is calculated using a one-way function. A one-way function is one where it is computationally infeasible to find two different inputs X and Y, such that the cryptographic hash of X is equal to the cryptographic hash of Y. The term “computationally infeasible” is one used in prior art to describe a mathematical procedure that cannot be performed in the practical sense because of the very large number of computational steps required. However, the term is not precise in that there is no prescribed number of computations above which a computation is said to be computationally infeasible and below which the computation is said to be computationally feasible. In general, a mathematical procedure is said to be computationally infeasible if the cost or time to perform the necessary computations is beyond reasonable human means, e.g., if all the computers in the world linked together couldn&#39;t solve the problem in a billion billion billion years. 
     Location specific information may be a combination of location specific information stored in signature token  500  and location specific information derived algorithmically. The table of contents in a multimedia title is one example of location specific information that can be omitted from signature token  500 . In other words, signature token  500  does not need to store an address or location of the table of contents because a simple procedure exists for always finding the table of contents given a standard starting point. 
     A portion of the data records 1 through n in signature token  500  will reference data in one or more data objects in the multimedia title. The signature token generation module employs a process to select a subset of different data objects (referenced by the object-property pairs in the table of contents) from a multimedia title to be validated. This process will be described in more detail below. It is desirable to have an element of randomness in this process although strictly speaking random in this process is not required. Once the subset of data objects in the multimedia title have been identified, a subportion of the data in each data object is selected and the locations of these subportions of data (denoted L 1 , L 2 , . . . , Ln) are used by the signature token generation module to read the data associated with each subportion. The signature token generation module then issues a service request to the cryptographic subsystem to generate a cryptographic hash value Hi on each subportion of data referenced by location information Li. The cryptographic hash value, Hi, is then stored in data record i together with the location information, Li. After the header and data records  1  through n have been created the signature token generation module issues a service request to the cryptographic subsystem to calculate a cryptographic hash value on the signature token, except for the digital signature. The signature token generation module then issues a service request to the cryptographic subsystem to calculate a digital signature on the signature token, using the cryptographic hash value calculated on the signature token and the private key of the multimedia company. The digital signature is then stored in the signature token. 
     The signature token validation module will randomly select and validate a subset of the data records in the signature token thus introducing an element of randomness into the validation process in accordance with a preferred embodiment of the present invention. Once the subset of data records has been randomly selected, the signature token validation module will process each data record on a record-by-record basis. The location specific information, L, in the data record is used to read the referenced data from the CD-ROM. A service request is then issued to the cryptographic subsystem to generate a cryptographic hash value, H, on the referenced data. This calculated cryptographic hash value is then compared for equality with the reference cryptographic hash value, H, stored in the data record. If the cryptographic hash values are equal, the process then continues. Otherwise, processing may be halted with an indication that validation has failed. After each data record is processed, the signature token validation module issues a service request to the cryptographic system to cryptographically hash the signature token (except for the digital signature) that it previously read from the multimedia title. Then a service request is issued to the cryptographic subsystem to validate the digital signature. In accordance with a preferred embodiment of the present invention, the digital signature is encrypted with the public key of the multimedia company, stored in the signature token validation module. The encrypted value of the digital signature contains a hash-value-of-reference previously calculated on the valid signature token. The calculated hash value is then compared for equality with the so-obtained hash-value-of-reference. If the hash values are equal, then the signature token and digital signature are valid. Otherwise, the signature token and digital signature are not valid. Those skilled in the art will recognize that the subject invention can be practiced using any digital signature method without departing from the spirit of the invention. 
     The digital signature also can be calculated on a cryptographic hash value representing the root of a tree of cryptographic hash values, e.g., a binary tree of cryptographic hash values as described in U.S. Pat. No. 4,309,569, “Method of Providing Digital Signatures”. By storing n-1 additional intermediate cryptographic hash values in the signature token, m of the possible n data objects in the signature token can be validated using m*log2n hashing operations instead of n hashing operations, which for small n may be more advantageous. A method of calculating the tree of cryptographic hash values is described in U.S. Pat. No. 4,309,569 and in U.S. Pat. No. 5,231,666, “Cryptographic Method For Updating Financial Records”. 
     With reference now to FIG. 6, a block diagram of a signature token generation module and a signature token validation module is depicted in accordance with a preferred embodiment of the present invention. Signature token generation module  600  includes generation module  602  and cryptographic subsystem  604 . Signature validation module  606  includes a validation program  608  and a cryptographic subsystem  610 . Generation program  602  in signature token generation module  600  selects data (including data in randomly selected data objects) in the multimedia title to be validated. Generation program  602  reads data from the multimedia title and processes the data by issuing repeated service requests to cryptographic subsystem  604 . These repeated service requests to process data are used to build a signature token. Similarly, validation program  608  in signature token validation module  606  randomly selects (for subsequent processing and validation) a subset of the data records in the signature token generated by signature token generation module  600 . This data is read from the CDROM and is processed by issuing repeated service requests to cryptographic subsystem  610  to validate the signature token. 
     Cryptographic subsystem  604  provides the following cryptographic services to generation program  602 : (1) initialize random number generator, (2) generate random number, (3) generate hash value, (4) generate digital signature, and (5) verify digital signature. A verify digital signature function is provided so that once a signature token is generated, generation program  602  can validate the signature token to insure that the signature token can be correctly processed by cryptographic subsystem  610  and signature token module  606 . Such a verification function provides a high integrity process in creating multimedia titles with embedded signature tokens. Cryptographic subsystem  610  in signature token validation module  606  supports validation program  608  by providing the following services: (1) initialize random number generator, (2) generate random number, (3) generate hash value, and (4) verify digital signature. The random number generation is employed to randomly select data records in the signature token to be validated. Algorithms and procedures for generating random numbers, generating hash values, and for generating and verifying digital signatures are well know within the prior art. 
     The random number generator function can be implemented using the pseudo random integer generator supplied in Appendix C of American Standard Institute (ANSI) Standard X9.17, “Financial Institution Key Management (Wholesale)” as specified in Appendix 3 of Federal Information Processing Standard (FIPS) 186. 
     The initialize random number generator function is a function that causes a secret seed value to be generated within the random number generator or alternatively to be provided as an input to the random number generator. A simple method for initializing the random number generator is to employ a free-wheeling counter in combination with a series of requests to a human who interacts with the initialize random number generator function via a workstation keyboard and display. The user is repeatedly prompted to enter a character at the keyboard. Each time the random number generator function gets control, it reads the free-wheeling counter and this value is combined with a value stored in an accumulator. The final accumulator value is taken as the secret seed value. Because of small differences in human response time, the value of the free-wheeling counter is unpredictable, and therefore the resulting seed value will be random. 
     The generate hash function can be implemented using one of several algorithms, including the MDC-2 or MDC-4 algorithms described in U.S. Pat. No. 4,908,861 entitled “Data Authentication Using Modification Detection Codes Based on a Public One Way Encryption Function” or using the hashing algorithm in FIPS 180, “Secure Hash Standard.” 
     The generate digital signature and verify digital signature functions can be implemented with the RSA public key algorithm using ISO Standard 9796 “Digital Signature Scheme Giving Message Recovery” or by using signature generation and signature verification algorithms in FIPS 186, “Digital Signature Standard.” 
     Although the depicted embodiment employs a public key algorithm, which is an asymmetric algorithm, the digital signature can be based on a symmetric algorithm such as the Data Encryption Standard (DES). 
     With reference now to FIG. 7, a flowchart of a process for generating signature tokens in a signature token generation module is depicted in accordance with a preferred embodiment of the present invention. The process begins by receiving a multimedia title with the signature token (step  700 ). Thereafter, the process fixes variable N and M such that N is the maximum number of data records to be created for the signature token that is to be produced, and M is the maximum record data length in bytes of each selected data object (step  702 ). For example, N=1,000 and M=1,000 are possible values for N and M. The process then locates and reads the table of contents or equivalent information contained in the multimedia title (step  704 ). This information is called “D1”. In accordance with a preferred embodiment of the present invention, a 128 bit MDC, designated MDC 1, is calculated on the data D 1  (step  705 ). Using the table of contents as necessary, the first logo screen is located and read from the multimedia title (step  706 ). The logo screen contains the name of the multimedia title and is designated “D2”. A 128 bit MDC, designated MDC 2, is calculated on the data D 2  (step  707 ). 
     Using the table of contents, the process then determines the number of multimedia object-property pairs, S, contained in the multimedia title (step  708 ). An object-property is data pointed to by the object-property entry in a table of contents. S is calculated as S=S&lt;1&gt;+S&lt;2&gt;+ . . . +S&lt;T&gt;, where S&lt;i&gt; denotes the number of properties associated with multimedia object “i”, and “T” denotes the number of multimedia objects within the multimedia title. The process then sets n=min (N,S), the minimum of N and S (step  710 ). Typically, S will be much larger than N so that N=n will generally hold true. The process then sets R=n−2 and X=1 (step  712 ). Thereafter, an object-property pair is randomly selected from the multimedia title; the data corresponding to each object-property pair is located and read, and the locations(s) of the data are saved (step  714 ). “D3” denotes the information corresponding to the object-property pair (or the first n bytes of information) in the randomly selected object-property, which ever is less. L 3  denotes the information in the table of contents employed to locate and read the data corresponding to the randomly selected object-property pair. In effect, the process selects one of the S object-property pairs (excluding the table of contents and the logo screen) and then at the next iteration randomly selects one of the S- 1  remaining different object-property pairs with the previously selected object-property pair being excluded and so on and so forth. 
     The process then calculates the MDC on the data or data object referenced by the selected object-property pair (step  716 ). In accordance with a preferred embodiment of the present invention, a 128 bit MDC is calculated on the data associated with the object-property pair using the method described in U.S. Pat. No. 4,908,861 entitled “Data of Authentication Using Modification Detection Codes Based on a Public One Way Encryption Function”. The MDC values calculated on values D3 through Dn are denoted MCD 3 through MCDn, respectively, as the process loops through (steps  714  and  716 ). The process determines whether X=R (step  718 ). If X is not equal to R, the process sets X=X+1 (step  720 ) and returns to step  714 . This continues until R=n−2 different object property pairs have been processed. 
     When X=R, the process then proceeds to build a signature token, such as signature token  500  depicted in FIG. 5, consisting of a header, n data records, and a digital signature (step  722 ). The token type (e.g., “multimedia signature token”) and n (number of data records) is stored within the header. In the first data record, the data location and the hash value are set to the constant value “table of contents” and the calculated value of MCD 1, respectively. The term “table of contents” is stored in the data location sub-field in lieu of location information because the signature token validation module always knows the location of the table of contents in accordance with a preferred embodiment of the present invention. In the second data record in the signature token, the data location and hash value are set to the constant value “logo screen” and the calculated value of MDC2, respectively. The term “logo screen” is stored in the data location sub-field in lieu of location information because the signature token validation module is able to calculate the location of the logo screen from the information found in the table of contents in accordance with a preferred embodiment of the present invention. The data locations and hash values in data records  3 ,  4 , . . . , n are set to (L 3 , MDC3), (L 4 , MDC4), . . . , (Ln, MDCn), respectively. Note also that the hash values H 1  through Hn in data records  1  though n of the signature token are equal to the MDC values: MDC1 through MDCn, respectively. 
     Furthermore, the signature token also includes space for a digital signature in accordance with a preferred embodiment of the present invention. An RSA digital signature based on ISO Standard 9796 might typically require from 512 to 2048 bits of storage space. A DSS digital signature based on FIPS 186 requires 320 bits of storage space. At step  722 , the digital signature portion of the signature token is presently uninitialized. Thereafter, the process calculates a digital signature for the signature token with the multimedia company&#39;s private key (step  724 ). More specifically, a 128 bit MDC is calculated on the portion of the signature token consisting of the header and the n data records. This calculation may be performed using the process described in U.S. Pat. No. 4,908,861 entitled “Data Authentication Using Modification Detection Codes Based on a Public One Way Encryption Function”. 
     Thereafter, a digital signature is calculated on the MDC value using the private key of multimedia company in accordance with a preferred embodiment of the present invention. The digital signature could be calculated with an RSA private key in accordance with ISO standard 9796 or with a DSA private key in accordance with FIPS 186. Those skilled in the art will recognize that private keys of different lengths can be employed to calculate the digital signature, and that digital signatures of different lengths can be stored in the signature token in accordance with a preferred embodiment of the present invention. Thereafter, the digital signature is stored in the signature token and the process terminates. 
     With reference now to FIG. 8, a flowchart of a process for validating multimedia titles in a validation program is depicted in accordance with a preferred embodiment of the present invention. This process is employed within the signature token validation module  606  of FIG.  6 . The process begins by receiving a multimedia title with the embedded signature token (step  800 ). The process then fixes variable R, where R in this flowchart is the number of data records to be randomly authenticated (step  802 ). For example, R may be any value, such as 3, 4, 5, etc., but will generally be a small value in order to minimize the required processing time. Thereafter, the process reads the embedded signature token (step  804 ). In accordance with a preferred embodiment of the present invention, the table of contents may be used to locate and read the embedded signature token. 
     The process then locates and reads the table of contents or equivalent information contained in the multimedia title (step  806 ). This information is called “D1”. The process then calculates a 128 bit MDC on the table of contents, D1 (step  808 ). This calculation may be performed in various ways. For example, the process described in U.S. Pat. No. 4,908,861, entitled “Data Authentication Using Modification Detection Codes Based on a Public One Way Encryption Function” may be used. The process then validates the MDC calculated on the table of contents against the MDC-of-reference stored in the signature token (step  810 ). The 128 bit MDC calculated in step  808  is compared with H 1  in the first data record in the signature token. The process then determines whether the two values are equal (step  812 ). If MDC is not equal to H 1 , the process then indicates that the title is invalid (step  814 ). In accordance with a preferred embodiment of the present invention, an invalid multimedia title so-detected by the signature token validation module causes an indicator or indication to be set, but does not halt processing. However, the present invention could be practiced using an implementation wherein the processing is halted as soon as an invalid condition is detected, which would not depart from the spirit of the present invention. 
     If, however, MDC is equal to H 1 , the process then locates and reads the first logo screen that is displayed to a user in the multimedia title (step  816 ). The table of contents may be used to locate and read this logo screen. The logo screen contains the name of the multimedia title, and this information is called “D2”. Next, an MDC is calculated on the data comprising the logo screen (step  818 ). A 128 bit MDC is calculated in accordance with a preferred embodiment of the present invention. The process then validates the MDC calculated on the logo screen against the MDC stored in the signature token (step  820 ). The 128 bit MDC calculated in step  818  is compared with H 2  in the second data record in the signature token. The process then determines whether the two values are equal (step  822 ). If MDC is not equal to H 2 , the process then indicates that the title is invalid (step  824 ). The process then sets Y=1 (step  826 ). 
     The process also sets Y=1 if MDC is equal H 2  (step  826 ). The process then randomly selects and reads one of the n-2 remaining data records in the signature token (step  828 ). The data records are selected from data record  3  through data record n, inclusively. Each data record is associated with and refers to all or a portion of the data for a signal object-property pair in the multimedia title. The process then reads the data OP 1  associated with the object-property pair pointed to by the selected data record (step  820 ). The data location information in the data record is used to locate and read the data OP 1  associated with the referenced object-property pair in the multimedia title. 
     Next, the process calculates a 128 bit MDC on the selected data OP 1  (step  832 ). The process then validates the MDC calculated on the data OP 1  against the corresponding MDC, or hash value H, stored in the data record read from the signature token (step  834 ). In step  834  the 128 bit MDC calculated in step  832  is compared with the corresponding MDC, or hash value H, recovered from the data record. If the calculated MDC and stored MDC are equal, control is passed to step  838 . If the MDC values are not equal, the process indicates that the title is invalid (step  836 ) and control is passed to (step  838 ). The process determines whether Y=R (step  838 ). If Y is not equal to R, the process sets Y=Y+1 (step  839 ) and returns to step  828 . This continues until R data records have been randomly selected from among data records  3  through n in the signature token, and processed. When Y=R, the process then proceeds to validate the digital signature and signature token. Next, the process reads the digital signature in the signature token (step  840 ). 
     Thereafter, the process accesses the multimedia company&#39;s public key, which is stored as a fixed constant in the signature token validation module (step  842 ). The process then validates the signature using the public key (step  844 ). A 128 bit MDC is calculated on the portion of the signature token consisting of the header and the n data records. When an RSA digital signature is employed, the original 128 bit hash value H is recovered from the RSA digital signature using the process described in ISO standard 9796 utilizing the RSA public key. Thereafter, the 128 bit MDC calculated on the signature token including the header and the n data records are compared with the 128 bit hash value H. If these MDCs are equal, then the multimedia title is accepted as valid. Otherwise, the process indicates that the title is invalid. When a digital signature based on FIPS  186  is employed, the signature is validated by following the steps outlined in FIPS  186 , which are different from those used to validate an RSA digital signature. 
     The process then accepts the title or handles the title invalid condition (step  846 ). If the title is indicated as being invalid, several actions may be taken in accordance with a preferred embodiment of the present invention. For example, the multimedia title may be rejected, the multimedia title may be accepted, but the user is given a warning screen; the multimedia may be accepted, but the user may be required to start over. Of course, the signature may be validated before the table of contents, logo screen, and randomly selected data records are checked in accordance with a preferred embodiment of the present invention. Depending on the implementation other logical structures other than the table of contents or logo screen may or may not be checked. 
     The processes depicted in FIGS. 3-8 may be implemented by those of ordinary skill in the art within the data processing system depicted in FIGS. 1 and 2. The processes of the present invention also may be implemented in a program storage device that is readable by a data processing system, wherein the program storage device encodes data processing system executable instructions coding for the processes of the present invention. The program storage device may take various forms including, for example, but not limited to a hard disk drive, a floppy disk, an optical disk, a ROM, and an EPROM, which are known to those skilled in the art. The processes stored on a program storage device are dormant until activated by using the program storage device with the data processing system. For example, a hard drive containing data processing system executable instruction for the present invention may be connected to a data processing system; a floppy disk containing data processing system executable instructions for the present invention may be inserted into a floppy disk drive in the data processing system; or a ROM containing data processing system executable instructions for the present invention may be connected to the data processing system via a card or adapter connected to an I/O slot. 
     While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.