Role-based access control
Role-based access control (RBAC)   is an approach to restricting system access to authorized users. It is a newer alternative approach to mandatory access control (MAC) and discretionary access control (DAC).
Prior to the development of RBAC, MAC and DAC were considered to be the only known models for access control: if a model was not MAC, it was considered to be a DAC model, and vice versa. Research in the late '90s demonstrated that RBAC falls in neither category.
Within an organization, roles are created for various job functions. The permissions 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. Unlike context-based access control (CBAC), RBAC does not look at the message context (such as where the connection was started from).
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 (ACLs) 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.
When defining an RBAC model, the following conventions are useful:
- S = Subject = A person or automated agent
- R = Role = Job function or title which defines an authority level
- P = Permissions = An approval of a mode of access to a resource
- SE = Session = A mapping involving S, R and/or P
- SA = Subject Assignment
- PA = Permission Assignment
- RH = Partially ordered role Hierarchy. RH can also be written: ≥
- A subject can have multiple roles.
- A role can have multiple subjects.
- 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, thus it can be used to achieve appropriate segregation of duties. For example, the same person should not be allowed to both create a login account for someone, and also be allowed to authorize the procedure.
A subject 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, FreeBSD, Solaris, Oracle DBMS, PostgreSQL 8.1, SAP R/3 and many others effectively implement some form of RBAC.
In an organization with a heterogeneous IT infrastructure and requirements that span dozens or hundreds of systems and applications, using RBAC to manage sufficient roles and assign adequate role memberships becomes extremely complex without hierarchal creation of roles and privilege assignments. Alternate strategies for large scale assignment of privileges to users are discussed in this white paper: Beyond Roles: A Practical Approach to Enterprise User Provisioning. Newer systems extend the older NIST model  to address the limitations of RBAC for enterprise-wide deployments. Several academic papers exist as well as at least one commercial system Beyond NIST.
 See also
- Lattice-based access control (LBAC), equivalent to mandatory access control (MAC).
- Security label
- Security classification
- Covert channel
- Chinese wall
- Blind credential
- Sudo (superuser do) Unix program
- Identity Driven Networking
- XACML A Attribute Based Access Control (ABAC) model which incorporates RBAC
- Ferraiolo, D.F. and Kuhn, D.R. (October 1992). Role Based Access Control - 15th National Computer Security Conference (PDF), 554-563.
- Sandhu, R., Coyne, E.J., Feinstein, H.L. and Youman, C.E. (August 1996). "Role-Based Access Control Models" (PDF). IEEE Computer 29 (2): 38-47. IEEE Press.
- Ravi Sandhu, Qamar Munawer (October 1998). How to do discretionary access control using roles - 3rd ACM Workshop on Role-Based Access Control, 47-54.
- Sylvia Osborn, Ravi Sandhu, and Qamar Munawer (2000). Configuring role-based access control to enforce mandatory and discretionary access control policies - ACM Transactions on Information and System Security (TISSEC), 85-106.
- Sandhu, R., Ferraiolo, D.F. and Kuhn, D.R. (July 2000). The NIST Model for Role Based Access Control: Toward a Unified Standard - 5th ACM Workshop Role-Based Access Control, 47-63.
- FAQ on RBAC models and standards
- Role Based Access Controls at NIST - huge US government website with lots of information on the theory and implementation of RBAC
- XACML core and hierarchical role based access control profile - OASIS XACML standard. (PDF file)
- RBAC Microsoft's article