Role-Based Access Control

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In computer systems security Role-Based Access Control (RBAC) is an approach to restricting system access to authorized users. It is a newer and alternative approach to Mandatory Access Control (MAC) and Discretionary Access Control (DAC).

RBAC also differs from the traditional MAC and DAC. Earlier MAC and DAC were the only two known models of access control. If a model is not MAC, it is assumed to be a DAC and vice-versa. But research in late 90s proved that RBAC neither falls in the category of MAC nor DAC.

Within an organization, roles are created for various job functions. The permission to perform certain operations ('permissions') are assigned to specific roles. Members of staff (or other system users) are assigned particular roles, and through those role assignments acquire the permissions to perform particular system functions.

Since users are not assigned permissions directly, but only acquire them through their role (or roles), management of individual user rights becomes a matter of simply assigning the appropriate roles to the user, which simplifies common operations such as adding a user, or changing a user's department.

RBAC differs from access control lists (ACL's) used in traditional discretionary access control systems in that it assigns permissions to specific operations with meaning in the organization, rather than to low level data objects. For example, an access control list could be used to grant or deny write access to a particular system file, but it would not say in what ways that file could be changed. In an RBAC based system an operation might be to create a 'credit account' transaction in a financial application or to populate a 'blood sugar level test' record in a medical application. The assignment of permission to perform a particular operation is meaningful, because the operations are fine grained and themselves have meaning within the application.

With the concepts of role hierarchy and constraints, one can control RBAC to create or simulate Lattice-Based Access Control (LBAC). Thus RBAC can be considered a superset of LBAC.

When defining an RBAC model, the following conventions are useful:

  • U = User = A person or automated agent .
  • R = Role = Job function / Title which defines an authority level.
  • P = Permissions = An approval of a mode of access to a resource.
  • S = Session = A mapping involving U,R and / P
  • UA = User Assignment.
  • PA = Permission Assignment
  • RH = Partially ordered role Hierarchy. RH can also be written: >
  • A user can have multiple roles.
  • A role can have multiple users.
  • A role can have many permissions.
  • A permission can be assigned to many roles.

A constraint places a restrictive rule on the potential inheritance of permissions from opposing roles. For example the same person should not be allowed to both create a log-in account for someone, and also be allowed to authorize the procedure.

Thus, using set theory notation:

  • PA is a subset of or is equal to P x R and is a many to many permission to role assignment relation.
  • UA is a subset of or is equal to U x R and is a many to many user to role assignment relation.
  • RH is a subset of or is equal to R x R

The notation: x > y means that x inherits the permissions of y.

A user may have multiple simultaneous sessions with different permissions.

The use of RBAC to manage user privileges within a single system or application is widely accepted as a best practice. Systems including Microsoft Active Directory, SELinux, Oracle DBMS, PostgreSQL 8.1, SAP R/3 and many others effectively implement some form of RBAC.

Use of RBAC to manage user entitlements across multiple applications, however, is much more controversial. This is because users are often unique, and so the task of defining sufficient roles and assigning adequate role memberships in an organization with a heterogeneous IT infrastructure, in order to capture user privilege requirements, as those requirements span dozens or hundreds of systems and applications, becomes extremely complex. This problem, and alternate strategies, are discussed in a white paper: Beyond Roles: A Practical Approach to Enterprise User Provisioning.

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