Abstract:
The invention is a system and method for delegating security permission evaluation from a client computer to remote network service (e.g., a security server). The centralization of permission evaluation allows performance enhancements using rules compilation and better manageability. An application on a client machine may request a permission to access a resource at runtime and provide evidence data to a security server. The permission evaluation (the decision) is executed by the network service and enforced locally on the client machine. When the application runs on top of a virtual machine, its security manager may be used to hide all of the client-side processes, and thus providing the extra information to the network service in order to locally enforce the results.

Description:
FIELD OF INVENTION 
     The invention relates to a system and method for extending a client security infrastructure to transparently delegate, during application runtime, the evaluation of security permissions to network services. 
     BACKGROUND 
     Permission evaluation is the concept of applying a set of rules to grant or deny access to resources, such as files, directories or other pieces of information on a computer. Virtual machine (VM), implemented according to a runtime standard, may request permissions to their security manager in order to access these various resources. A security manager installed on a client machine enables a custom security policy to be set for an application. For example, in an ECMA-335 (Common Language Infrastructure) VM, Code Access Security (CAS) is the security manager mechanism that limits the access an application code has to protected resources. CAS is implemented locally at each computer where the VM resides. CAS uses local policies with code evidence to define permission and permission sets that represent the application rights to access various system resources. At application runtime CAS compares requested permission with one or more security policies. Unauthorized actions are prevented from executing using these security checks. Other VM, like Java, use similar mechanisms, to evaluate application permissions. 
     In the past, three types of application permissions have been developed, that is, products with very basic access control, products with complex access control rules within an application, and products with no access control. Very basic access control (e.g., multiple permissions&#39; flags encoded as bits and stored with a file entry) may bare little resemblance to an organization&#39;s requirements. As such, basic control may be suitable for a file system but not enough for a more complex environment such as a financial system. However, products with complex access control rules within applications are often difficult or even impossible to modify by the end-user of the application (e.g. enterprise hosting a web service). Finally, some products do not have any kind of access control. 
     Even applications providing access controls are often insufficient or incompatible with the user requirements, with the end result that they are often unused or even turned off. This situation has lead to the creation of new security standards and new security toolkits. These toolkits share properties that include, access control rules that are external to applications, rules resolution (e.g., decision making) that are internal to applications, rules that are human readable (e.g. ASCII, XML), rules that are mostly generated by tools, rules that can be complex (e.g. they can contain XPath expressions, regular expressions, scripts, etc.), and rules that can consume assertions made by other services. XACML (eXtensible Access Control Markup Language) is an example of such a language. SAML (Security Assertion Markup Language) is an example of a specification to consume/produce security assertions. 
     XACML is a standard for defining a general policy language used to protect resources as well as an access control decision language. Policy language allows administrators to define the access control requirements for their application resources. 
     SAML is an XML-based framework for Web services that enables the exchange of authentication and authorization information among business partners. 
     The addition of more complex security tools and decisions on a client machine, while useful, also have their drawbacks. In performing extensive security processes, the client system may result in overall performance slow down. Parsing and evaluating the required files and expressions within the client machine can be very time consuming, not to mention that many client machines of a network could be simultaneously taking the same action. In some cases the same files and expressions are evaluated many times for the same user and resource, a clearly inefficient situation. 
     As such, there is a need for evaluating complex security rules and decisions with less affect on client computer performance. There is a need to provide better overall performance for large-scale adaptation of access controls. The main disadvantage of the current implementation being that access control polices are inefficiently implemented for a large number of systems because maintenance and modifications to access control rules on each client machine becomes more difficult as more users and rules are added to the system. 
     SUMMARY 
     Various aspects of the invention overcome at least some of these and other drawbacks of known systems. The invention is an improvement in the way complex access control rules can be used from both a performance and a manageability point of view. Performance is a key element to the large-scale adoption of new access control technologies. By way of example, a request for accessing a file may be delegated to a remote server, in order to provide an authorization for the requested permission. Thus, a security decision usually made on a local machine may be made at a network location and the result (e.g., pass/fail) may be sent back to the local machine for enforcement. Performance is gained by using dedicated resources and new optimizations to evaluate permissions. Manageability is gained by the centralization of the evaluation from many client machines to a few centralized network services. 
     According to one aspect of the invention, a network service may be implemented on a security server to receive security rules (logic and data) from other servers and network services; store the received rules; compile the rules with its own access control policies; receive code evidence and a request for permission to access a resource and forward the evaluation result to the client machine. 
     According to another aspect of the invention, a client computer runs application code; requests permission to perform an operation to a network service; provides application code evidence with request; receives access control instructions; enforces received access control instruction on application. Client computer may include a security manager for requesting permissions and enforcing its results. Security manager on a client machine (e.g., CAS) may transparently invoke a network connection and forward request and code evidence to the security server. In the latter case the application itself does not have any knowledge of where and how the security decisions are made. This makes it possible to use the invention with existing applications using a security manager, for example in all .NET and Java applications. 
     Further aspects of the invention recognize some important facts that limit today&#39;s performance. A large part of access control rules, both the logic and its data, are static in nature. Many details are included in the definitions (e.g. XACML) or file formats (e.g. XML) to make them human readable. Rules logic and data generally do not change drastically over time, the proof being that most of them are currently hard-coded in the older-model applications. According to an aspect of the current invention, a security server may compile the static parts of the access control rules into managed or native code. The compilation may be used to perform more advanced optimizations, for example, a true/false evaluation at compilation time (e.g., invariant elimination), which incurs little to no runtime cost. A change in a rule definition (e.g., a file update) can trigger a re-compilation of the rule at the security server, thus ensuring that the compiled rule is up to date before being executed. The time required to compile rules is rapidly gained back by reduced rule execution time and some information on which the rules are applied change more often (e.g., user, role, time, etc.). This dynamic information may not be compiled, because they exist as variables on which the compiled rules are executed against. 
     The invention takes advantage of network resources to make security decisions that may then be enforced locally. The invention implements security policies and security instructions from a security server or other source, therefore relieving client machine resources for other processes. These and other objects, features and advantages of the invention will be apparent through the detailed description of the embodiments and the drawings attached hereto. It is also to be understood that both the foregoing general description and the following detailed description are exemplary and not restrictive of the scope of the invention. 
    
    
     
       DETAILED DESCRIPTION OF DRAWINGS 
         FIG. 1  is a high-level block diagram for a system, according to one embodiment of the invention. 
         FIG. 2  is a diagram for a method of a client server process, according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The invention enables significant performance gains by compiling complex access control rules using a network service (e.g., security server), wherein several client applications can share the same compiled access control rules. Centralized sharing of the same rules works to eliminate the risk of having different applications, rules, and versions coexisting on the same network. It also makes it a lot easier to update the access control logic since it is centralized into a few, possibly a single, component. 
       FIG. 1  is a high level block diagram of a client computer and server, among other things. A client computer  100  may include application code(s)  102 , virtual machine (VM)  104 , which may include a security manager  106  among other things. A network service acting as a security server  120  may include a rule compiler  114 , rule evaluator  116  and a storage for the compiled rules logic and data  118 . Other network resources may be linked to the network  110 , including but not limited to, application server(s)  130 , database server(s)  140 , directory service(s)  150  and other client computers. The network of  FIG. 1  is scalable to accommodate multiple client computers with one or more security servers. 
     Security server  120  may be located in logical and/or physical proximity to client computer  100  or to the other servers  130 ,  140 ,  150 . Client computer  100  may encompass other types of client devices and should not be limited to personal computer. For example, client machine may be a mobile device, like a cell-phone, or other device, like an embedded system. Client computer may also operate in an off-line mode if needed. In an off-line mode the permission evaluation may use cached information from previous communication with the servers, and consider their results as valid as long as a response timestamp is still valid. 
     During client computer operations the application  102  and/or security manager  106  of the virtual machine  104  on client computer  100  may request permission(s) to access application resources (e.g., files, directories, process). Permissions may represent the right to access various system and network resources based on security policies. A set of permissions may be determined for an application code based on the security policy and evidence provided by the application code including, but not limited to, identity, publisher, source (e.g., URL, website), origin (e.g., Internet, Intranet) and/or other information about the application seeking permission. With an ECMA-335 VM, the application and its assemblies (e.g., .DLL files, .EXE files) may specify the requested permissions using declarative or imperative security. Declarative security allows the developer of the application code to insert permission attributes into the code itself whereas imperative security may allow the developer to specify permissions dynamically within source code. Both types are well known in code development and execution. The present invention is able to delegate the permission evaluation to a network service without requiring change to existing VM and security manager, enabling existing applications to gain both performance and manageability advantages without extensive changes. 
     According to one aspect of the invention, an application  102  running on a client computer  100 , may request permissions from a network service running on a security server. This request may include at least, the requested permission (e.g. access file “secret.doc”) and some evidences to help evaluation (e.g. current user is “Bob”). 
     Alternatively, an application  102  may be executed under a virtual machine  104 . In this case the application&#39;s declarative and/or imperative security may request permissions from the VM security manager  106 , which can delegate the permission evaluation to a network service running on a security server  120 . The request may include the XML representation of the permission, the current call stack, application domain, and assembly&#39;s evidences. In this case changes to the application itself are minor due to the transparency of the security manager&#39;s actions. 
     In both cases, a security server  120  can use the rule compiler  114  to compile its stored security policies from storage  118  and any other rules it receives from other servers  130 ,  140 ,  150 . This allows static access control rules and definitions to be compiled for more efficient security evaluation when permissions are requested from client computers  100 . Using the code evidences and permission request supplied by the client computer  100  the compiled rules may be executed, with a greater speed than interpreted rules. In the event that a rule does change, the rule can trigger a re-compilation at the security server. 
       FIG. 2  is a flow diagram for client and server operations, according to an aspect of the invention. A security server  120  may receive access control policy, security policy and/or other security information from application host server(s), client computer(s), and/or other sources (operation  50 ). The information can either be pulled from the security server (e.g., retrieving an update from a remote database server at a specified time) or pushed from a remote server (e.g., an update when a new user is being added to the directory services). Such pull and/or push mechanisms may be configured on each security server  120  and does not require updates to every client computer  100 . Received information may be stored at security server storage  118  or other location, for example a remote database server  140 . Security server  120  may have logic incorporating the ability to compile and execute access control security. Security server  120  may compile the rules, using the rule compiler  114  and the information contained in storage  118 , before, during or after an application is instantiated on client computer  100  (operation  52 ). Client computer begins execution of an application (operation  54 ), which includes one or more request for permissions (operation  56 ). The request may be made directly to security server  120  or indirectly via the security manager  106  of the client computer  100 . The security server  120  receives the request for permission, either directly from the application runtime or indirectly via security manager  106 . In both cases, the security server  120  receives request accompanied with application evidence. The evidence information may be sent to security server via XML standards. The evidence is combined with the permission request and provided to the security server  120 . The security server  120  may parse, interpret, and evaluate which actions to take based on the information (operation  58 ). After access control has been remotely evaluated, the security server  120  forwards (operation  60 ) the resulting information to client computer  100  for local enforcement (operation  62 ). 
     Delegated permission evaluation allows the security permissions to be judged outside the client machine. Further optimization may be made by security server  120  in specific contexts. For example, the repetitive pattern of asking for network resources can be cached. Thus, a response to request for a web service (e.g. service discovery) from a client computer  100  can be made almost instantly when presented a second or subsequent time. Caching the results of the web service for a policy defined time can lower bandwidth usage and improve performance without sacrificing security. Caching can also be implemented at the client computer  100 . In this case the security server  120  may add a timestamp within a response. This timestamp can indicate an interval of time, between now and a specified time, for which the result is known to be valid. Client-side caching may be useful when client computers  100  are executing in an offline mode. 
     A further optimization technique is possible if parts of some rules logic are expected to change often. For example, it may be that a large part of the rule is static and a minor part is dynamic. Splitting such rules into several smaller rules and compiling the rules independently (e.g., one assembly per rule file) can improve performance in the case that some (top) rules are being generated very frequently or automatically for each request. The change of one or more rule(s) can trigger a selective recompilation at security server  120 . The impact of the changes is still very small compared to the gains made by compiling the rules. 
     Thus, the client machine&#39;s environment may remain unchanged with respect to evolving security rules. The client computer  100  supplies the evidence in order for the security server  120  to evaluate the security permissions and the client computer  100  enforces the policies sent back from the security server  120 . The client computer  100  requests permissions and receives permissions with little regard as to where the security decision came from. The client may be further optimized when applications are executed on a virtual machine where the security manager can be extended to provide such services transparently. 
     A networked permission also has the advantage of being very generic. The client computer  100  may have limited (little to none) knowledge about the rules used to evaluate the requested permission. Such rules can be changed without affecting the local applications, even while the local applications are executing on the client computer  100 . 
     In the foregoing specification, the invention has been described with reference to specific embodiments thereof. Various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.