Label Types

The Trusted Extensions software defines two types of labels: sensitivity labels and clearance labels. A sensitivity label indicates the security level of an entity and is usually referred to as a label. A clearance label defines the upper boundary of a label range and is usually referred to as a clearance.

Sensitivity Labels

The Trusted Extensions software uses zones to contain classified information at various levels. Each level is associated with its own zone that has a sensitivity label. The sensitivity label specifies the sensitivity of the information in that zone and is applied to all of the subjects and objects in that zone. A label might be something like CONFIDENTIAL, SECRET, or TOP SECRET. A subject is an active entity, such as a process, that causes information to flow among objects or changes a system's state. An object is a passive entity that contains or receives data, such as a file or device. All processes that run in a zone, all files that are contained in a zone, and so on, have the same sensitivity label as their zone. All processes and objects have a sensitivity label that is used in mandatory access control (MAC) decisions. By default, sensitivity labels are visible in the windowing system.

Clearance Labels

The security administrator assigns a clearance to each user. A clearance is a label that defines the upper boundary of a label range. For example, if you have a clearance of SECRET, you can access information that is classified at this level or lower, but not information that is classified at a higher level. A user clearance is assigned by the security administrator. It is the highest label at which a user can access files and initiate processes during a session. In other words, a user clearance is the upper boundary of a user's account label range. At login, a user selects his session clearance. The session clearance determines which labels a user can access. The session clearance sets the least upper bound at which the user can access files and initiate processes during that login session. The session clearance is dominated by the user clearance.