Labels and clearances consist of a single classification and zero or more compartment words. The classification portion of a label indicates a relative level of protection. When a label is assigned to an object, the label's classification indicates the sensitivity of the information that is contained in the object. When a clearance is assigned to a user, the classification portion of the clearance label indicates the user's level of trust.
Trusted Extensions supports Common IP Security Option (CIPSO) labels. Each label and clearance label has a classification field that allows 256 values, and a 256-bit compartments field. You cannot use 0 (zero) for a classification, so you can define a total of 255 classifications. For CIPSO labels, 240 compartment bits are available, for a total of 2240 compartment combinations. The components are illustrated in the following figure.
The ADMIN_HIGH label and the ADMIN_LOW label are administrative labels. These labels define the upper and lower bound of all labels on a system.
Each compartment word has one or more compartment bits assigned. The same compartment bit can be assigned to more than one word.
The textual format of a classification appears similar to the following:
CLASSIFICATIONS: name= TOP SECRET; sname= TS; value= 6;initial compartments= 4-5;
The compartment portion of a label is optional. Compartment words in a label can be used to represent different kinds of groupings, such as work groups, departments, divisions, or geographical areas. Compartment words can also further identify how information should be handled.
When initial compartments are part of the classification definition, then compartments are part of that label.
WORDS: name= A; compartments= 0; name= B; compartments= 1; name= CNTRY1; sname= c1; compartments= ~4; name= CNTRY2; sname= c2; compartments= ~5;
Possible labels from the preceding classifications and compartments include TS, TS A, TS B, and TS AB. A file with TS A would be available only to individuals who have the TS classification and the A compartment in their clearances. For an illustration, see Figure 1–3.