Method and system for enforcing access to a computing resource using a licensing attribute certificate

A licensing attribute certificate enables a trusted computing base to enforce access to a computing resource by a computer application. The licensing attribute certificate can contain enforcement data which limits the use of the computing resource. The licensing attribute certificate can also contain information allowing for the tracking of licensing data about the use of the computing resource. The use of a licensing attribute certificate to enforce access to a computing resource can allow products to be fielded which have their capability limited to a specific subset of functions. The enforcement data, the licensing data, and the data limiting the application to a specific subset of functions are cryptographically bound to the computing resource using a licensing attribute certificate according to the invention. Prior to allowing access to the computing resource by the computer application, a trusted computing base strongly authenticates that usage via the licensing attribute certificate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the authorized use of computing resources by computer applications. More particularly, the present invention relates to use of a licensing attribute certificate (LAC) to provide cryptographic binding between a computing resource and attributes related to a computer application, and to provide strong authentication by a trusted computing base controlling the computing resource.

2. Background Information

In a typical untrusted computer environment, a computer application can use available computing resources with little or no authorization or accountability. Examples of such computing resources include a modem or network interface. Another example of such computing resources includes a cryptographic token, which provides cryptographic resources to the computer application.

FIG. 1adepicts a typical computer system100made up of several “layers”101, with two layers130and132consisting of a number of different modules102,103,104, and105. Each layer represents a collection of one or more modules at a particular abstraction level in a hierarchy of software code development. Each module represents a collection of computer instructions which perform a particular operation on the data which the module receives, producing some data output from the module. At the top layer130, module102can represent a computer application running on a computer of a user115. Via a user interface in this example, module102receives input110from user115. The input110could, for example, represent ordering and payment information in an electronic commerce transaction.

Similarly, module103receives data item112, data item114, and data item116as inputs. The module103processes the data items112,114, and116, and produces data outputs118and120. These outputs118and120, in turn, become inputs for computing resource A106. Computing resource A106then processes its data inputs118,120,122, and124to produce resource output126, which is returned to module102.

In the example system shown inFIG. 1a, layer130might be written in a well known high-level language, such as C or C++. Layer132can comprise libraries of lower-level functions, that would be usable by other applications in addition to module102. These libraries could also be written in a high-level language.

In general, layer134represents any atomic computing resources that process data. Layer134can be cryptographic computing resources, such as those found on a cryptographic token. Layer134can also be computing resources that send signals to hardware devices, such as a display or some other peripheral device. Layer134can also be computing resources that transform data received from user115.

A cryptographic token provides the ability to perform cryptographic operations on data. Some examples of cryptographic operations include symmetric encryption (secret key) operations, asymmetric encryption (public key) operations, key exchange operations, hash operations, digital signature operations, and key wrapping operations.

FIG. 1bdepicts an example of a system150of functional layers that contain computing resources specifically designed for providing cryptographic processing. This system, which does not contain the invention, can be contrasted with the system shown inFIG. 4, which does contain the invention. In the example shown inFIG. 1b, user152interacts with a user interface in the computer application171of application layer160. In this example, computer application171represents the highest level of abstraction; that is, an interface with user152. As a result of input170from user152, computer application171generates inputs172and174for a mid-level application programmer interface (API) layer162. In this example, the mid-level API layer162comprises two different mid-level libraries, cryptographic API library A173and cryptographic API library B175. These API libraries173and175communicate with a low-level API library177in low-level API layer164via inputs176and178. Finally, the low-level API library177communicates with the cryptographic resources via inputs180and182to software drivers comprising hardware token code stack179or software token code stack181in driver software level166. Hardware token code stack179interfaces with hardware cryptographic token reader183. Hardware cryptographic token reader183sends data over data path184to hardware cryptographic token187in order for the data to be cryptographically processed therein. The hardware cryptographic token187contains trusted computing base (TCB)191which is used to provide computing resources to computer application171in the form of cryptographic operations from cryptographic computing resource A193. Another example of a TCB which can be used to provide cryptographic operations from cryptographic computing resource B197to computer application171in system150is TCB195made accessible via software token189. Software token189, consisting, for example, of a floppy disk, is accessed via software token code stack181and token reader185, and contains the necessary information to allow computer application171to access the cryptographic operations made available via low-level API library177.

Early cryptographic systems used a secret key approach to secure data. In these systems, each user had the same cryptographic key which was used for both encryption and decryption of the data. As a result, the key needed to be kept secret or else the system could be compromised (thus the name secret key cryptography). In contrast, relatively recent advances in cryptography have led to cryptographic systems which use a mathematically related pair of keys. In these systems, one key is kept private by the user, while the other is made public (thus the name public key cryptography). These key pairs allow for algorithms that provide confidentiality (via encryption); and authentication, integrity, and nonrepudiation (via digital signatures).

The deployment of public key cryptography, especially in a public key infrastructure (PKI), relies heavily on public key certificates. A public key certificate (or just “certificate”) contains the public key of a user, along with information that allows a relying party to evaluate whether or not to trust a user's digital signature produced using the private key corresponding to that public key. In particular, the certificate contains the digital signature of a Certification Authority (CA). In general, the CA is a secure, standards-based, and trusted entity that provides certificate, token, user registration, and directory management services. In particular, the CA issues certificates to subscribers. A CA's signature on a certificate indicates that the CA has verified the identity of the user whose certificate it has signed, and the CA's signature also binds the identity of the user to the public key appearing in the certificate.

The X.509 standard of the International Telecommunication Union (dated June 1997) defines an “attribute certificate” as a “set of attributes of a user together with some other information, rendered unforgeable by the digital signature created using the private key of the certification authority which issued it.” Thus, an attribute certificate contains information to supplement the identity information in a public key certificate.

In addition, the X.509 standard defines “strong authentication” as “[a]uthentication by means of cryptographically derived credentials”. The X.509 standard discusses the property of some public key cryptosystems (PKCSs) in which the enciphering and deciphering steps can be reversed, and goes on to state that this property “allows a piece of information which could only have been originated by X, to be readable by any user (who has possession of [the public key of X]). This can, therefore, be used in the certifying of the source of information, and is the basis for digital signatures. Only PKCS which have this (permutability) property are suitable for use in this authentication framework.” In other words, strong authentication can only be achieved with a PKCS in which the public key reverses the transformation accomplished using the private key, and vice versa.

The Trusted Computer System Evaluation Criteria from the United States Department of Defense (DOD) defines a TCB as “the totality of protection mechanisms within a computer system . . . the combination of which is responsible for enforcing a security policy. It creates a basic protection environment and provides additional user services required for a trusted computer system.” An appropriately designed cryptographic token can, for example, contain a TCB. Appropriate design might include features such as a tamper proof case, nonmodifiable firmware, and zeroization of sensitive data upon intrusion detection. A secure operating system is another example of a TCB.

In the past, systems have been suggested which provide access control over various distributed computer resources. For example, in U.S. Pat. No. 5,339,403 issued to Parker, a system is described which requires a user to present a privilege attribute certificate to a computer application in order to access that application. However, the system according to Parker assigns the privilege attribute certificate to the user, only providing access control over the user to some subset of target computer applications. The system according to Parker does not provide strong authentication as the means for allowing access from a computer application to a computing resource. Furthermore, the system according to Parker utilizes a very complex shared secret (i.e. secret key) approach. The Parker approach relies upon encryption of the privilege attribute certificate using the shared secret key. A secret key system contains inherent key management problems and key compromise problems. In particular, a purely secret key system has no recovery mechanism following a compromise. The only way to recover (i.e. the only way to again provide security after compromise of a secret key) is via a physical redistribution of secret key material.

In addition, prior systems have been developed which provide access control over portable data storage media in a manner which allows tracking the usage of certain data. For example, commonly owned U.S. Pat. No. 5,457,746 issued to Dolphin on Oct. 10, 1995, describes a system which allows a publisher to define and enforce attributes related to encrypted files stored on external media. The attributes in this system could relate to such things as usage of particular data, time-related usage of a resource, or number of log-ons.

For many reasons, it is desirable to control the use of computing resources by a computer application through the use of strong authentication. For example, certain computing resources available on cryptographic tokens, if accessible by the computer application, would render the token unable to be exported from certain countries (such as the United States) unless restricted to use by approved computer applications. If those cryptographic operations could be successfully limited to use by approved computer applications using strong authentication, the cryptographic token could then be exported.

Similarly, it may be desirable to limit the accessibility to cryptographic operations contained in a cryptographic token for licensing reasons, which would require a metering of those operations. For example, a provider of cryptographic products might desire to limit access to operations on a cryptographic token to those entities who have properly licensed those operations from the provider. Alternatively, it may be desirable for developers of software products to control accessibility to their products using strong authentication techniques provided by the use of an LAC, in conjunction with separate computing resources.

SUMMARY OF THE INVENTION

According to the invention, a licensing attribute certificate (LAC) enables strong authentication techniques to be utilized for enforcing access to computing resources, via the use of standards-based public key techniques. Enforcing can include, for example, controlling access to computing resources, metering usage of computing resources, selectively enabling certain functions available from computer resources, or any combination of these and other functions. The LAC can contain information allowing for the tracking of licensing data about the use of computing resources. Those computing resources can be contained within a trusted computing base (TCB). The TCB can be in any of a number of forms, including contained within a cryptographic token or a secure operating system. The LAC can further contain information which limits the use of the available computing resources. This would allow products to be fielded, such as cryptographic tokens which contain cryptographic computing resources, which have their capability limited to a specific subset of functions. The use of a LAC in accordance with the invention can provide a cryptographically strong way of limiting access by a computer application to a specific subset of functions.

In one embodiment of the invention, a computer application developer receives a LAC from a vendor of a computing resource. A vendor can include any person or entity which provides computing resources. The developer embeds the LAC, containing a vendor's digital signature, into a computer application. The public key corresponding to the vendor's private key can be built in to the software library that provides the interface between the computer application and the TCB. Alternatively, the public key corresponding to the private key of the vendor can be built in to the TCB containing computing resources.

In yet another embodiment, separate public keys can be built in to both the software library and the TCB. When the computer application attempts to use a computing resource within the TCB, the library seeks to verify a first digital signature of the vendor and the TCB seeks to verify a second digital signature of the vendor. In addition to checking that both of the digital signatures are valid, checks could be made on the enforcement data within the licensing attribute certificate to determine whether access to the computing resources within the TCB can take place.

This invention provides a method for enforcing access by a computer application to a computing resource controlled by a trusted computing base, using standards-based public key techniques. The invention uses strong authentication to enforce that access control. The invention thus overcomes the complexities in the data exchanges involved in prior art systems. The invention also provides strong authentication in the use of a computing resource by a computer application, and eliminates the security risks particularly associated with systems which implement secret key approaches. The invention also provides a method for tracking usage of a computing resource using a LAC. Furthermore, the invention provides a method for allowing computer application developers to control access to their products via use of a LAC. In addition, the invention provides a method for restricting the usage of a computing resource to authorized functions.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, a method and system for cryptographically binding a computing resource and a licensing attribute certificate (LAC) allows only authorized usage of the computing resource. The computing resource can, in one embodiment, be located within a trusted computing base (TCB). In another embodiment, the computing resource can be located outside of the TCB. In either case, the operations available from a computing resource cannot be accessed without a cryptographic verification by the TCB of the computer application's use of that computing resource. In a further particular embodiment, a LAC is used to provide strong authentication of a computing resource by a cryptographic token via a digital signature.

FIG. 2depicts a basic system involving a LAC, according to the invention. User equipment205contains TCB208, computer application210, and LAC220. User equipment205can include any type of computational device. Some examples include a personal computer, a personal digital assistant, or a machine with embedded computing capability. In general, user equipment represents any equipment used by a person or other entity (such as a corporation) that contains at least one computer application and at least one computing resource.

LAC220inFIG. 2contains attribute information about computing resource226, in the form of enforcement data222. Enforcement data222facilitates enforcement of the use of the computing resource and can contain, for example, information about how and when the computing resource can be used. Enforcement data222can further contain information about what operations available from the computing resource can be used. LAC220also includes digital signature224computed using a private key.

TCB208inFIG. 2contains computing resource226, to which TCB208controls access, as represented by the switch in data path230. TCB208also contains a public key212, corresponding to the private key that was used to compute digital signature224. Prior to computer application210gaining access to computing resource226, TCB208must authenticate LAC220using public key212. If the authentication of LAC220succeeds, TCB208will permit computer application210to access computing resource226along data path230.

FIG. 3adepicts a method according to the present invention as applied to enforcement of authorized usage (e.g. licensing) of computing resources. Other applications of the invention can include, for example, exportability compliance or allowing selective usage of a computing resource.

InFIG. 3a, vendor301of a computing resource360(shown inFIG. 3c) first produces enforcement data312that can, for example, correspond to particular rights afforded to a specific computer application developer303(shown inFIG. 3b). For example, the vendor of a computing resource might wish to limit the access to that computing resource to only a certain application. Alternatively, the vendor of the computing resource might wish to grant access to a subset of all of the functionality available from the computing resource. For example, where the computing resource is a hardware cryptographic token, the vendor might wish to only allow digital signature operations to be executed and would therefore need to disallow encryption operations.

InFIG. 3a, vendor301uses its private key310to compute digital signature316on enforcement data312using sign process314. Sign process314(as well as other sign processes discussed herein) can be implemented using any of the well understood techniques for computing a digital signature. For example, the Digital Signature Algorithm, as specified in Federal Information Processing Standard Publication (FIPS PUB)186could be used to calculate digital signature316. Alternatively, the RSA algorithm could be used.

Digital signature316, corresponding to the particular computing resource360, is combined with enforcement data312to form LAC318. Vendor301then transmits LAC318to computer application developer303. The transmission of LAC318to computer application developer303can occur using any methods and apparatus, including both networked and non-networked approaches. The LAC could be sent via a network, such as, for example, a Local Area Network (LAN), a Wide Area Network (WAN), or via the Internet. Transmission methods can include such things as, for example, electronic mail from the vendor to the computer application developer. Alternatively, the LAC can be posted on a bulletin board system (BBS), or can be stored in a directory of a computer system by the vendor and retrieved by the application developer using any type of retrieval technique, such as, for example, Telnet.

InFIG. 3b, computer application developer303generates computer application source code330, which is combined with LAC318. Computer application source code330and LAC318can be combined by using compile process332, which creates an association between the computer application source code330and LAC318. In another embodiment, a computer application and a LAC can be combined by providing an entry in a system registry of a computer operating system.

InFIG. 3b, the compilation of computer application source code330and LAC318generates an executable application334which can contain computer application333with LAC318embedded within it. Once compiled, the executable application334can be made available for distribution to users.

InFIG. 3c, user305can acquire the executable application334(which, in this example, contains the version of computer application333that can be executed on a computer) through any of several means including, for example, retail store purchase, electronic purchase (e.g., via the Internet), or any other software distribution mechanism. User305can make a purchase of, for example, a CD-ROM containing executable application334, or can purchase and then download executable application334electronically. User305loads executable application334onto the user's computer340and runs executable application334. In this example, executable application334needs to utilize computing resource360contained within TCB345(which can be contained within computer340).

However, in order to gain access to computing resource360, digital signature316contained within LAC318must be verified by TCB345. TCB345performs verify process370using public key354in combination with enforcement data312to verify digital signature316. The success of verify process370means that digital signature316in LAC318is valid. In addition, supplemental enforcement data356, which may be contained in a database within computer340(i.e. external from the LAC), could be utilized to provide further control over accessibility to computing resource360as further described with reference to FIG.10. Once LAC318is validated, executable application334being used by user305will then have access to computing resource360.

In order to verify digital signature316, TCB345must have public key354. In one embodiment, depicted inFIG. 3c, vendor301can embed public key354in TCB345. In an alternative embodiment, TCB345can receive public key354via a separate X.509 identity certificate path which is transmitted along with LAC318.

FIG. 4depicts a system400according to one embodiment of the invention which includes computing resources specifically designed for providing cryptographic processing. This embodiment represents one aspect of the SPYRUS S2CA, made and sold by SPYRUS, Inc. of Santa Clara, Calif., which is a secure, standards-based, and trusted certification authority (CA) that provides certificate, token, user registration, and directory management services.

In system400inFIG. 4, user480installs and runs executable application411on the user's computer. Executable application411can contain a number of different types of computer functionality, including such things as user interfaces, software libraries, and device drivers. In this example, the executable application411can contain LAC403which can be embedded in computer application402. Also included in executable application411can be executable libraries, including PKCS #11application programmer interface (API)404and Microsoft CryptoAPI (CAPI)406. PKCS #11is a nonproprietary, technology-neutral programming interface for cryptographic tokens such as smart cards and PCMCIA cards. CAPI is an interface that allows developers to build applications that use system-level certificate management and cryptography.

Computer application402communicates with PKCS #11API404via data path412and with CAPI406via data path414. Upon execution of particular instructions in either PKCS #11API404or CAPI406which require functionality contained within cryptographic computing resource484, LAC403can be passed via either data path416or data path418to the vendor specific library, such as the SPYRUS Extensions (SPEX) library408.

InFIG. 4, SPEX library408performs library authorization800which can include using library public key410, library supplemental enforcement data417, and LAC403in verify and validate process415. Further detail on library authorization800can be found in FIG.8. The library authorization step provides an interim level of enforcement that does not involve a cryptographic token at all. This can be useful, for example, for minimizing the number of operations to be performed by the computing resources. As long as verify and validate process415succeeds, SPEX library408will be permitted to communicate with hardware token code stack430, in attempting to make use of cryptographic computing resource484. In this example, cryptographic token470contains cryptographic computing resource484which SPEX library408accesses via hardware token code stack430and smart card reader460.

In this embodiment, control of the use of the cryptographic operations within the cryptographic computing resource484occurs within the boundaries of TCB474which is contained within cryptographic token470. These cryptographic operations can be carried out on a cryptographic token. For example, a LYNKS PCMCIA card or a Rosetta smart card, both made and sold by SPYRUS, Inc. of Santa Clara, Calif., provides all of the above mentioned cryptographic operations to a computer application. Other examples of a hardware cryptographic token include a separate hardware board inside of a computer or an external hardware peripheral device. Alternatively, these cryptographic operations can be carried out via the use of a software cryptographic token, which can comprise a computer processor executing instructions and accessing data stored on a data storage device such as a floppy disk. For example, the software version of the Fortezza™ cryptographic token, also made and sold by SPYRUS, Inc. of Santa Clara, Calif., provides all of the above mentioned cryptographic operations to a computer application.

Prior to allowing any use of the cryptographic operations available in the cryptographic computing resource484, TCB474performs token authorization900(described further below with respect toFIG. 9) which includes using token public key490, token supplemental enforcement data477, and LAC403in verify and validate process482. The success of verify and validate process482confirms the cryptographic binding between cryptographic computing resource484and LAC403. This allows TCB474to enforce the proper use of the cryptographic operations contained in cryptographic computing resource484by computer application402.

The enforcement of the proper use of the cryptographic operations contained in cryptographic computing resource484can occur via the enforcement data contained in LAC403. Enforcement data permits enforcement of various conditions represented by the data. Enforcement data can, for example, be defined such that computing resources are only available for a specified number of uses, or such that only certain functions within the computing resources are available. The bit pattern in the LAC inFIG. 5represents one embodiment of the data used to provide enforcement. In another embodiment, a LAC can be implemented using the X.509 attribute certificate format.

LAC403inFIG. 5contains enforcement data520which can include attribute data associated with both cryptographic token470and SPEX library408. Token attribute data502can, for example, identify the cryptographic operations on token470which are available to computer application402via SPEX library408. Token digital signature504can be used by token470to validate token attribute data502and to enforce the proper use of the cryptographic operations by computer application402. Library attribute data506can represent the functionality available to computer application402via SPEX library408. Library attribute data506can be further logically divided into accessible tokens data508and sub-functionality data510. These can allow even finer granularity to be defined for the subset of functions identified by library attribute data506. For example, sub-functionality data510can be used in enforcing the available SPEX library functions such as, for example, limiting the functions available to computer application402to only encryption and decryption, but not authentication.

In addition to the attribute data, LAC403inFIG. 5contains library digital signature514. Library digital signature514can allow the SPEX library408to validate the LAC, and thereby control the availability of the library's functions.

FIG. 6depicts a first step in the assembly of LAC403according to an embodiment of the invention. First, the computing resource vendor generates token attribute data502associated with the particular computer application for which the LAC is being created. Once token attribute data502has been determined, the vendor uses token private key602to digitally sign token attribute data502using sign process604which produces token digital signature504.

Next, the vendor specifies information that determines the accessibility to the functions on the token. In the LAC403, accessible tokens data508represents this information. The vendor of cryptographic tokens can define, for example, accessible tokens data508such that access to the computing resources would be limited to only those resources on that vendor's cryptographic tokens. After accessible tokens data508has been generated, the vendor then sets sub-functionality data510which can allow even finer granularity enforcement of the available resources. Once assembled, token attribute data502, token digital signature504, accessible tokens data508, and sub-functionality data510comprise enforcement data520.

FIG. 7depicts a subsequent step in the assembly of LAC403in the present embodiment. Once all of the enforcement data520associated with the token and the library has been generated for LAC403, the vendor uses a library private key702to digitally sign enforcement data520using sign process704. The result is library digital signature514, which is then appended to enforcement data520. The overall data assembly, consisting of token attribute data502, token digital signature504, accessible tokens data508, sub-functionality data510, and library digital signature514comprise LAC403.

It may be desirable to use two different key pairs (each consisting of a public and a private key) for the two signing processes604and704in FIG.6andFIG. 7, respectively. This means that token private key602in FIG.6and library private key702inFIG. 7are different. This may be the case, for example, if the vendor of the token differs from the vendor of the library. Alternatively, the two key pairs (and thus the two private keys602and702) can be the same. This may be the case, for example, if one vendor distributes both the token and the library.

FIG. 8illustrates library authorization process800performed by SPEX library408, as discussed generally above in regards to verify and validate process415shown in FIG.4. Upon receiving LAC403, SPEX library408separates library digital signature514from the remainder of LAC403. The enforcement data520is input to verify process840, along with library digital signature514and library public key410. If the library digital signature514is properly verified, the library408permits processing to continue. If the library digital signature514is not properly verified, SPEX library408notifies computer application402that an error has occurred. If an error does occur, the library can take a variety of courses of action such as using an alternate resource.

Once library digital signature514has been verified, the library408checks library attribute data506against library supplemental enforcement data417. This can, for example, determine whether the library408is permitted to access the token or tokens designated in the accessible tokens data508and determine whether library408can perform the particular operations designated in sub-functionality data510. If the validation of either accessible tokens data508or sub-functionality data510fails, data path860will not be enabled, which will prohibit the library408from further communications with the cryptographic token470.

FIG. 9illustrates token authorization900performed by token410, as discussed generally above in regards to verify and validate process482in FIG.4. The token470separates the token digital signature504from LAC403. Token attribute data502is input to verify process940, along with token digital signature504and token public key480. If the token digital signature504is properly verified, the token470permits processing to continue. If the token digital signature504is not properly verified, the token470notifies library408that an error has occurred. Library408then notifies computer application402of the error, and computer application402will handle the error. Computer application402can notify user480of the error, or can attempt to process the error without notifying user480.

Once token digital signature504has been verified, token470checks token attribute data502against token supplemental enforcement data477in validate process950. This determines whether token470is permitted to perform the particular operations designated in token attribute data502. If the validation fails, data path960is not enabled, which will prohibit the use of token470by computer application402.

FIG. 10depicts LAC1000, according to an embodiment of the invention, which can be used for tracking usage of a particular computing resource. In this embodiment, the LAC1000exists in a system at a certification authority (CA) which issues certificates. InFIG. 10, token attribute data1070contained in the LAC can contain usage data for a computing resource. This usage data allows the usage of the computing resource to be metered. For example, token attribute data1070inFIG. 10contains a maximum certificates to issue field1072. Token supplemental enforcement data1074, which resides in a database that can be maintained outside of a TCB, contains certificates issued counter1076. Certificates issued counter1076reflects the number of certificates that have been issued by the CA. During validate process1050, maximum certificates to issue field1072is compared against certificates issued counter1076. If certificates issued counter1076has exceeded the value in maximum certificates to issue field1072, further usage of the computing resource will be disallowed.

The check of certificates issued counter1076against maximum certificates to issue field1072can occur inside of the TCB. Once checked, the TCB would then update certificates issued counter1076, store the updated value within the TCB, and send the updated certificates issued counter1076back to the database. In an alternative embodiment, the updating of the certificates issued counter1076can occur external from the TCB.

In another embodiment, the usage data can, for example, correspond to a maximum number of accesses by a computer application to a computing resource. In yet another embodiment, the usage data can, for example, correspond to a maximum number of cryptographic operations that can be performed by a computing resource which provides cryptographic functionality.

The embodiments of the LAC described so far represent only a few of many possible models of LAC usage. As the model inFIG. 11ashows, vendor1101can distribute LAC1102(comprising enforcement data1104and digital signature1106) to application developer1108. Application developer1108creates computer application1112into which LAC1102is embedded, as previously described. Vendor1101also distributes computing resource1115and vendor public key1119(both contained within TCB1110) to the user, who installs the TCB1110in user equipment1114. The user also installs computer application1112, containing LAC1102, in user equipment1114. Prior to being able to use computing resource1115, however, TCB1110would need to properly validate LAC1102using vendor public key1119contained in TCB1110.

FIG. 11bshows a model which differs somewhat from that shown inFIG. 11a. InFIG. 11b, application developer1120creates computer application1122and has no interaction at all with vendor1101. In contrast to the model inFIG. 11a, the user sends request1124from user equipment1114to vendor1101. In response, vendor1101prepares LAC1103and transmits this directly to the user. The user installs both LAC1103and TCB1110on user equipment1114, in addition to computer application1122. In this model, similar to the model shown inFIG. 11a, prior to being able to use computing resource1123, TCB1110must properly validate LAC1103using vendor public key1121.

Although the invention has been described for a licensing attribute certificate used by a CA, it applies to a wide range of computing applications where enforcing authorized usage of resources is desired. For example, usage of computer aided drawing (CAD) software could be enforced with a LAC. In addition, access to a CD-ROM containing data could be enforced with a LAC. Thus, the present invention is not limited to the precise embodiments described above. For example, while a LAC could be compiled with a computer application as described above, a system and method according to the invention could just as easily be implemented in which a LAC exists in a separate file from an executable application. Similarly, other authentication means besides digital signatures could be used. Additionally, the counter discussed in the method for using a LAC to track usage of a resource might be contained within the cryptographic token itself.

It is clear that various changes and modifications may be made to the embodiments which have been described, more specifically by substituting equivalent technical means, without departing from the spirit and scope of the invention. The embodiments presented are illustrative. They are not intended to limit the invention to the specific embodiments described and shown in the attached figures. Instead, the invention is defined by the following claims.