Planning the Encodings File

The following practices help achieve the good organization required for a correct label_encodings(4) file that may be extended safely later.

Plan to leave room to add items.

Plan ahead for extending the file later, which may save you from needing to create a whole new file if additions are needed. For example, you could number classifications in increments of 10 to allow intermediate classifications to be added if the need arises. For the same reason, consider spacing compartment bit numbers for possible later additions.

If your site uses inverse compartments and markings, plan to reserve some initial compartment and marking bits for later definition.

If you need to learn more about inverse compartments and markings see the DIA document, Compartmented Mode Workstation Labeling: Encodings Format . See also "Setting Default and Inverse Words".

Determine classifications for the site.

As described under "Classifications", the total number of classification values that you can use is 254. Do not use classification 0.

The classification part of the label represents the relative sensitivity of one classification over another. Irrespective of what you call the human readable names associated with each classification, the system treats a classification whose value is 10 as more security sensitive than a classification whose value is 2.

For CLASSIFICATIONS, COMPARTMENTS, the security administrator role can later change human readable names but cannot change the values without potentially serious complications.

Different WORDS can not be specified with the same classification value. Each classification WORD must be higher or lower than one or more others because all labels must dominate or be dominated by some other label. Assigning the same number to more than one name would create levels of security that are named differently but are treated as the same level by the system. No two labels can evaluate to the same level.

Decide on compartments.

Decide how data and programs are grouped and whether or not any data or programs can be intermixed. For example, perhaps weather data should not be seen by programs dealing with personnel files, but weather data should be accessible to programs that deal with targeting problems.

At this point, keep people out of the picture. Think in terms of what, not who.

Design the names.

CLASSIFICATIONS and WORDS in the label_encodings(4) file have two forms: a mandatory long name and an optional short name. Long names for classifications and any words appear by default in the information label portion of the CMW label. Short names for classifications and any words appear by default within brackets in the sensitivity label portion. Labels on windows are truncated after the real estate on the top of the window is used up, and, even though you can view the full label, so labels on window system objects can be read more easily if you keep the long and short names as short as possible while still retaining meaning.

Arrange the relationships.

Compartments and markings are intrinsically non-hierarchical, even though they can be configured to have hierarchical relationships. They represent bits (or flags) attached to objects or subjects in the system. The combination of those bits determines the accessibility of a subject or object. Before setting up relationships, read very carefully the example section of Compartmented Mode Workstation Labeling: Encodings Format several times, walking through the examples.

One way to make this step easier is to use a large board and pieces of paper marked with your classifications, compartments and markings, as shown in Figure 1-6. With this method, you can visualize the relationships and rearrange the pieces until they all fit together.

When the command, chk_encodings(1M), is used to check label encodings files for errors, it checks syntax only. With the -a option chk_encodings can be used to analyze and report on relationships between labels.

Figure 1-6 Example Planning Board for Label Relationships

Decide which clearances will be available to which users.

Use the following table, if desired, for planning clearances.

Table 1-14 Clearance Planner

CLASS	COMP	COMP	COMP	COMP	COMP	OOMP	Notes

Arrange the labels that will be formed from the classifications and compartments in order of increasing sensitivity.

Associate the definitions for each word with an internal format of integers, bit patterns, and logical relationship statements.

Decide what colors should be associated with labels.