【正文】 amline even transform their anizations. More recently panies have begun using web technology to service the public as well as private and internal clients. Web sites are set up to segregate some information from the general public, providing it to only selected or private clients. Typically, public inter is cordoned off from the general public by having user accounts and passwords. Additionally, Web sites are now running inside the pany often created for and by employees. These internal private s or intras use the infrastructure and standards of the Inter and the World Wide Web but are cordoned off from the public Inter through firewalls. The Web can be used as an inexpensive yet powerful alternative to other forms of munications. A plethora of corporate information (., procedures, training materials, directories, forms) can be converted to electronic form and made available via the Web. With a single source for these materials the cost of maintenance is significantly reduced, while greatly simplifying the task of ensuring currency. Thus an objective of enterprise puting, creation of a pany wide system irrespective of the underlying information technology infrastructure can be fulfilled. Although the inter and intras can offer great benefits to a pany or government agency, security threats remain. To date enthusiasts tend to focus on how to link people and businesses, not on using the work as a way to run and manage businesses securely. Although existing Web servers can effectively provide all or nothing access to a particular Web site and a number of popular Web servers can even provide fairly fine grained access control, they provide very primitive tools to administer these controls from the perspective of a single enterprise. This paper describes the benefits of RBAC and an implementation of RBAC on the Web (RBAC/Web), and in particular as RBAC applies to an intra puting environment. This will provide Web administrators with a capability for the first time to centrally administer and regulate user access to information in a manner that is consistent with the current set of laws, regulations, and practices that face their business today. Although this paper focuses on intras, the benefits, concepts and implementation of RBAC/Web are also applicable to a pany’ s inter environment where restrictive access to information is desired. RBAC Description Rolebased access control (RBAC) [1], [2], [3], [4], [5] is an alternative to traditional discretionary (DAC) and mandatory access control (MAC) policies that is attracting increasing attention [6], particularly for mercial applications. The principal motivation behind RBAC is the desire to specify and enforce enterprisespecific security policies in a way that maps naturally to an anization39。s structure. Traditionally, managing security has required mapping an anization39。s structure. Each user is assigned one or more roles, where roles are based on the user39。s membership into roles that determine the privileges the user is permitted to perform. Security administration with RBAC consists of determining the operations that must be executed by persons in particular jobs, and assigning employees to the proper roles. The RBAC framework provides for mutually exclusive roles as well as roles having overlapping responsibilities and privileges. For example, some general operations may be allowed by all employees, while other operations may be specific to a role. Role hierarchies are a natural way of anizing roles within an anization and defining the relationship and attributes of the roles. Complexities introduced by mutually exclusive roles or role hierarchies as well as regulating who can perform what actions, when, from where, in what order, and in some cases under what relational circumstances, is all handled by the RBAC software. Separation of Duty RBAC mechanisms can be used by a system administrator in enforcing a policy of separation of duties. Separation of duties i