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1. Labels in Trusted Extensions Software 3. Making a Label Encodings File (Tasks) 4. Labeling Printer Output (Tasks) 5. Customizing LOCAL DEFINITIONS 6. Example: Planning an Organization's Labels Identifying the Site's Label Requirements Climbing the Security Learning Curve Analyzing the Requirements for Each Label Editing and Installing the label_encodings File Configuring Users and Printers for Labels |
Defining the Set of LabelsIn this section the set of labels is defined in lists that include all of the following required aspects of labels:
Planning the ClassificationsBecause the four labels are hierarchical, the four labels are encoded as hierarchical classifications. With the legal department's approval, the security administrator shortened the labels by omitting SecCompany Confidential: from the label names. Long classifications make labels hard to read in window frames. The name of a label is truncated from right to left in the window frames. Because the truncated names of all the label names above PUBLIC would begin with the words SECCOMPANY, the truncated names would be indistinguishable without manually extending the frame for each window. The security administrator defined the following labels:
Planning the CompartmentsThe group names will be encoded as non-hierarchical compartments. Compartments will be restricted to appear only in labels that have the NEED_TO_KNOW classification. Compartment restrictions are encoded in the ACCREDITATION RANGE section under COMBINATION CONSTRAINTS. User clearances will control which users can create files and directories that have a group name in the label. User clearances will also control which users can create documents that have a label with more than one group name along with the NEED_TO_KNOW classification. Planning the Use of Words in MACThe classifications and compartments in sensitivity labels and user clearances are used in mandatory access control (MAC). Therefore, the legal department's hierarchical labels and the group names need to be encoded as classifications and compartments so that they can be used in the labels that control which individual employees can access files and do other work. SecCompany, Inc. defines a sensitivity label with the PUBLIC classification, which is assigned the lowest value in the User Accreditation Range, and another sensitivity label with the INTERNAL_USE_ONLY classification with the next highest value above PUBLIC. An employee with no authorizations whose clearance is PUBLIC and whose minimum label is PUBLIC is able to use the system as follows:
Planning the Use of Words in Labeling System OutputWhen the sensitivity label of a printer job contains a group name compartment, the mandatory printer banner and trailer pages print the following text: Distribute Only To Group Name (Non-Disclosure Agreement Required) Planning Unlabeled Printer OutputThe Print Without Labels authorization allows a user or role to use the lp -o nolabels option to suppress the printing of top and bottom labels on body pages of a print job. The Security Administrator role can give the Print Without Labels authorization to everyone or to no one. The Print PostScript File authorization allows a user to submit a PostScript file to the printer. PostScript printing is usually not allowed because of the risk that a knowledgeable user can change the labels in the PostScript file. To permit technical writers to produce master copies of documents without labels printed on them, the Security Administrator role gives the Print Without Labels and Print PostScript File authorizations to all the writers. Planning for Supporting ProceduresThe security administrator creates security policies to enforce the labeling scheme. Rules for Protecting a REGISTERED File or DirectoryThe security administrator realizes that anyone with a clearance that includes the word REGISTERED can access any registered information anywhere in the company. Further precautions are needed. For example, users who have REGISTERED in their clearance must be instructed to use UNIX permissions to protect their files. Permissions should be set so that only the creator can look at or modify the file. The following example shows a user who is applying discretionary access control to protect the contents of a REGISTERED directory. Example 6-2 Using DAC to Protect Registered Information% plabel REGISTERED % mkdir registered.dir % chmod 700 registered.dir % cd registered.dir % touch registered.file % ls -l -rwxrwxrwx registered.file % chmod 600 registered.file % ls -l -rw------- registered.file As shown in the example, the user who creates a file or directory while working at an sensitivity label of REGISTERED needs to set the file's permissions to be read and write for the owner only. Directory permissions are set to be readable, writable, and searchable only by the owner. These permissions ensure that another user who can work at REGISTERED cannot read the file. Rules for Configuring PrintersThe following table shows how printers that are available to various work groups need to be configured. Table 6-1 Printer Label Range Example Settings in Various Locations
Rules for Handling Printer OutputPeople who have access to restricted printers will be instructed to do the following:
Planning the Classification Values in a WorksheetThe worksheet in the following table shows names and hierarchical values defined for the four classifications. Because the value 0 is reserved for the administrative ADMIN_LOW label, the value of the PUBLIC classification is set to 1. The values of the other classifications are set higher in ascending sensitivity. Note - The names of groups in the labels are specified later, as WORDS in the SENSITIVITY LABELS and CLEARANCES sections. Table 6-2 Classifications Planner
Planning the Compartment Values and Combination Constraints in a WorksheetThe following table defines the relationships between words and classifications. The relationships were determined by moving things around on the planning board in Figure 6-5. PUBLIC and INTERNAL_USE_ONLY can never appear in a label with any compartment. NEED_TO_KNOW can appear in a label with any of the compartments or all of the compartments. Table 6-3 Compartments and User Accreditation Range Combinations Planner
The security administrator uses the following table to keep track of which bits have been used for compartments. Table 6-4 Compartment Bit Tracking Table
Planning the Clearances in a WorksheetThe components of these labels are also assigned to users in clearances. The worksheet's Clearance Planner, Table 6-5, defines the label components to be used in clearances. Key to Table 6-5:
Table 6-5 Clearance Planner
* The highest possible label in the system consists of the highest classification and all of the defined compartments. Because no one should be able to access all information in all departments, this label is not in the user accreditation range. No one should be assigned this clearance. ** When working at the REGISTERED sensitivity label, the user should set permissions to restrict access to everyone except the owner. File permissions of 600 and directory permissions of 700 restrict access. Planning the Printer Banners in a WorksheetThe SecCompany legal department wants the following to appear on printer banner and trailer pages. SecCompany Confidential: The PRINTER BANNERS can be used to associate a string with any compartment that appears in the sensitivity label of the print job. In this encodings, only the NEED_TO_KNOW classification has compartments. The following table shows how the desired wording is specified as a prefix and assigned to each compartment. The abbreviation NTK is assigned to each channel so that the wording in the PRINTER BANNERS section includes the group name: SecCompany Confidential: group-name Table 6-6 SecCompany Printer Banners Planner
Planning the Channels in a WorksheetThe SecCompany legal department wants the following handling instructions to appear on printer banner and trailer pages. DISTRIBUTE ONLY TO group-name EMPLOYEES (NON-DISCLOSURE AGREEMENT REQUIRED) This goal is met by assigning in the CHANNELS section the same compartment bits that were assigned to group names earlier in this example. The SecCompany company plans to use the same group names both in the compartments and in the channels. The words that come before the channel name are specified as prefixes and the words that come after the channel name are specified as suffixes. The security administrator specifies prefixes and suffixes in the following worksheets. Table 6-7 SecCompany Channels Planner
Planning the Minimums in an Accreditation RangeThe following minimums must be set:
The SecCompany company wants employees to be able to use all the defined sensitivity labels. Also, the company wants to be able to assign the PUBLIC clearance to some employees. Therefore, the minimum sensitivity label and minimum clearance need to be set to PUBLIC. The minimum protect as classification is printed on printer banner and trailer pages instead of the actual classification from the job's sensitivity label. The minimum protect as classification can be set higher than the actual minimum classification. However, the SecCompany company requirements allow the minimum protect as classification to always be equal to the real classification of the print job's sensitivity label. The security administrator specifies the value PUBLIC for the minimum sensitivity label, minimum clearance and minimum protect as classification. Planning the Colors in a WorksheetThe color that is assigned to a label displays in the background whenever the name of the label appears at the top of a window. The lettering is displayed in a color that is computed by the window system to complement the background. In our example, the security administrator chooses to keep the colors already assigned to the administrative labels in the default label_encodings file. The administrator assigns green to PUBLIC, yellow to INTERNAL_USE_ONLY, blue to labels that contain NEED_TO_KNOW (with different shades of blue assigned to each compartment), and red to REGISTERED, as shown in the following table. Table 6-8 SecCompany Color Names Planner
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