Data processing: database and file management or data structures – Database design – Data structure types
Reexamination Certificate
2000-12-15
2003-11-11
Coby, Frantz (Department: 2171)
Data processing: database and file management or data structures
Database design
Data structure types
C707S793000, C707S793000, C713S182000, C715S252000, C715S252000
Reexamination Certificate
active
06647388
ABSTRACT:
PRIOR FOREIGN APPLICATION
This application claims priority from Japanese patent application number 11-358178, filed Dec. 16, 1999, which is hereby incorporated herein by reference in its entirety.
1. Technical Field
The present invention relates to a method for evaluating policy descriptions for access control, and for enforcing a condition portion for implementing the policy descriptions.
2. Background Art
Conventional, well known policy description means for accessing a data file are, for example, KeyNotes [BFIK99] (PolicyMaker [BRL96]), GACL [WL93] [WL98] and ASL [JSSB97] by ATT. These policy descriptions, which are rules used to determine whether to permit access, are based on a list of three elements (Subj, Obj, Op) that is called an access control list (ACL). This means that a subject (Subj) of an access is permitted to perform a specific operation (Op) for an access target (Obj). Therefore, in order to respond to all access requests, ACLs must be prepared for all possible combinations of the three.
To simplify the access control policy, the above policy description means describes pattern matching using a variable, and introduces the rule ACL(subj, Obj, Op)←Cond(subj, Obj, Op) in order to write a condition formula for limiting a variable. That is, since it is difficult and requires too much effort to prepare, in response to an access request, ACLs that correspond to each combination of three elements, an abstract of the policy is created by using a variable, and upon the receipt of a relevant access request for the variable, access control is exercised in accordance with a corresponding ACL.
Two different methods are used when describing an operation performed for a control target on an ACL: a method by which only operations that are permitted are described, and a method by which both operations that are and operation that is not permitted are described. The first method is used with the Closed World Assumption. According to the Closed World Assumption, when the applicable interpretation is that no available ACL corresponds to a particular access request, the specified operation is not permitted. Therefore, when in an ACL only those operations that are permitted are described, and an access request does not match any entry in the ACL, the requested operation is rejected unconditionally. The second method is used for GACL, and in this case, the Default assumption is that an operation is permitted so long as a distinctly negative operation is not requested.
Although policy evaluation methods may differ in various respects, all of the conventional policy evaluation systems return an evaluation decision as a binary, Yes or No, result. In other words, a value of 1 or 0 is returned in reply to a question ?-ACL(subj, obj, op).
As is described above, according to the policy evaluation techniques used for conventional access control, a policy evaluation performed in response to an access request produces a simple binary result, either Yes or No. That is, in response to an access request, the conventional technique determines only whether access should or should not be permitted. Thus, the conventional technique is not sufficiently flexible, and it can not provide a conditional response, such as a Yes (a conditional Yes) that is dependent on the establishment of a specific state.
Therefore, generally it is not possible to provide complicated access control that is dependent on various conditions, such as: the issuing of an instruction to permit access, the embedding of an electronic watermark in data that are read or the writing of an access log when data encoding or format conversion is to be performed, or the issuing of an instruction to permit access when a time condition is the controlling factor.
SUMMARY OF THE INVENTION
To resolve the above technical shortcomings, upon the receipt of an access request, one object of the present invention, when exercising access control, is not only to determine, basically, whether access should or should not be permitted, but also to evaluate for acceptability an access request for which access permission is dependent on the establishment of a specific condition.
It is another object of the present invention to recurrently evaluate a specific condition if it is requested that a condition that is being evaluated to grant access permission under a condition should establish the specific condition.
To achieve the above objects, according to the present invention, an access control system comprises: a resource document in which a policy description is stored that is associated with data stored in a data file; policy evaluation means for receiving an external request for accessing the data file, for extracting, from the resource document, the policy description that is associated with target data for the access request, and for evaluating the policy description to determine whether or not the access request is to be permitted; enforcement function verification means for, when an existing condition is such that the policy description can not be evaluated using only the information included in the policy evaluation means, determining whether the condition can be evaluated or can be established; and enforcement means for evaluating or establishing the condition that, in accordance with the enforcement function verification means, is capable of being evaluated or established.
A plurality of the enforcement means can be provided in accordance with the evaluation or the establishment of the condition, which can not be evaluated using only the information included in the policy evaluation means. When the plurality of enforcement means are provided, the enforcement function verification means further determines whether a condition that one of the enforcement means has received from the policy evaluation means can be evaluated or established. This arrangement is preferable because the contents of a condition can be coped with flexibly. For the verification process to be performed by an enforcement means that can evaluate or establish a condition, a list can be employed in which a component of the enforcement means and a condition governing an operation that the pertinent component can enforce are stored in correlation with each other.
When access of a different data portion is required in order to evaluate or establish a condition that is determined by the enforcement function verification means can be evaluated or established, the enforcement means issues, to the policy evaluation means, a request to access the different data portion. Upon the receipt of the access request from the enforcement means, as well as upon the receipt of an external access request, the policy evaluation means evaluates a policy description that is associated with data to be accessed. This arrangement is superior in that an access request can be recurrently issued to evaluate or establish the condition. The data portion may be either a different portion of a document to be accessed or a predetermined portion of another document.
The enforcement means includes: writing/alteration target detection means for detecting a data portion in the data file that is a target for writing or alteration, and for issuing an access request to the policy evaluation means; and writing/alteration execution means for, when in response to the access request access permission is received from the policy evaluation means, writing or altering the data portion, wherein the writing/alteration execution means prepares a desired function by using a plug-in. This arrangement is preferable because a complicated process for evaluating or establishing a condition can be flexibly coped with by adding a corresponding function using a plug-in. When an access target is an XML document, the writing/alteration execution means can be an XSL processor, which is a standard tool for reading XML data, and a conversion rule, for generating new XML data. In this case, plug-in software can be added to carry out a complicated process.
An access control method, for
Amano Tomio
Kudoh Michiharu
Numao Masayuki
Coby Frantz
Heslin Rothenberg Farley & & Mesiti P.C.
International Business Machines - Corporation
Kinnaman, Jr. Esq. William A.
Nguyen Cam Linh
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