Encoding MAC Words

As mentioned above, words on which mandatory access control must be performed must be associated with compartment bits, and must appear in the CLEARANCES: and SENSITIVITY LABELS: sections, and possibly in the CHANNELS:, PRINTER BANNERS:, and INFORMATION LABELS: sections. The word would appear in the CHANNELS: section if the word represents a handling channel. The word would appear in the PRINTER BANNERS: section if the word requires any special printer banner marking other than a handling channel caveat. The word would appear in the INFORMATION LABELS: section if it is desired that the word appear in information labels. It is conceivable that a mandatory access control word not appear in information labels, but that a codeword that implies the word could appear instead.

When encoded in the clearances:, sensitivity labels:, channels: and PRINTER BANNERS: sections, a mandatory access control word would be associated with only compartment bits. When encoded in the INFORMATION LABELS: section, the word could have associated both compartment and marking bits.

Consider the word A in Appendix B, Annotated Sample Encodings. This word, which appears with the name A in the clearances: and sensitivity labels: sections and the name (CH A) in the channels: section, is associated with compartment bit 0 being 1. Note that the word A in the information labels: section is also associated with compartment bit 0 being 1, but additionally has a marking bit associated, for a reason discussed below.

Some words that represent compartments, and would typically be expected to have only compartment bits associated, nonetheless require association with marking bits in information labelsB to establish a hierarchy with other information label words. In the INFORMATION LABELS: section, A has marking bit 7 associated. The purpose of marking bit 7 in the specification of A is to establish a hierarchy with A above WNINTEL (which is associated only with marking bit 7). The reason for this hierarchy is that the word WNINTEL was deemed unnecessary along with any word that directly represents or implies a compartment. The hierarchy prevents WNINTEL from appearing in a label with any such word.