The control objective for marking is: "Systems that are designed to enforce a mandatory security policy must store and preserve the integrity of classification or other sensitivity labels for all information. Labels exported from the system must be accurate representations of the corresonding internal sensitivity labels being exported."
DoD 5220.22-M, "Industrial Security Manual for Safeguarding Classified Information," explains in paragraph 11 the reasons for marking information:
Marking requirements are given in a number of policy statements.
Executive Order 12356 (Sections 1.5.a and 1.5.a.1) requires that classification markings "shall be shown on the face of all classified documents, or clearly associated with other forms of classified information in a manner appropriate to the medium involved." [DoD-5220.22-M]
DoD Regulation 5200.1-R (Section 1-500) requires that: ". . . information or material that requires protection against unauthorized disclosure in the interest of national security shall be classified in one of three designations, namely: 'Top Secret,' 'Secret' or 'Confidential.'" [Denning76] (By extension, for use in computer processing, the unofficial designation "Unclassified" is used to indicate information that does not fall under one of the other three designations of classified information.)
DoD Regulation 5200.1-R (Section 4-304b) requires that: "ADP systems and word processing systems employing such media shall provide for internal classification marking to assure that classified information contained therein that is reproduced or generated, will bear applicable classification and associated markings." (This regulation provides for the exemption of certain existing systems where "internal classification and applicable associated markings cannot be implemented without extensive system modifications." [Denning76] However, it is clear that future DoD ADP systems must be able to provide applicable and accurate labels for classified and other sensitive information.)
DoD Manual 5200.28-M (Section IV, 4-305d) requires the following: "Security Labels - All classified material accessible by or within the ADP system shall be identified as to its security classification and access or dissemination limitations, and all output of the ADP system shall be appropriately marked." [DoD-5000.29]
The control objective for mandatory security is: "Security policies defined for systems that are used to process classified or other specifically categorized sensitive information must include provisions for the enforcement of mandatory access control rules. That is, they must include a set of rules for controlling access based directly on a comparison of the individual's clearance or authorization for the information and the classification or sensitivity designation of the information being sought, and indirectly on considerations of physical and other environmental factors of control. The mandatory access control rules must accurately reflect the laws, regulations, and general policies from which they are derived."
There are a number of policy statements that are related to mandatory security.
Executive Order 12356 (Section 4.1.a) states that "a person is eligible for access to classified information provided that a determination of trustworthiness has been made by agency heads or designated officials and provided that such access is essential to the accomplishment of lawful and authorized Government purposes." [DoD-5220.22-M]
DoD Regulation 5200.1-R (Chapter I, Section 3) defines a Special Access Program as "any program imposing 'need-to-know' or access controls beyond those normally provided for access to Confidential, Secret, or Top Secret information. Such a program includes, but is not limited to, special clearance, adjudication, or investigative requirements, special designation of officials authorized to determine 'need-to-know', or special lists of persons determined to have a 'need-to- know.'" [7, para. 1-328] This passage distinguishes between a 'discretionary' determination of need-to-know and formal need-to-know which is implemented through Special Access Programs. DoD Regulation 5200.1-R, paragraph 7-100 describes general requirements for trustworthiness (clearance) and need-to-know, and states that the individual with possession, knowledge or control of classified information has final responsibility for determining if conditions for access have been met. This regulation further stipulates that "no one has a right to have access to classified information solely by virtue of rank or position." [7, para. 7-100] )
DoD Manual 5200.28-M (Section II 2-100) states that, "Personnel who develop, test (debug), maintain, or use programs which are classified or which will be used to access or develop classified material shall have a personnel security clearance and an access authorization (need-to-know), as appropriate for the highest classified and most restrictive category of classified material which they will access under system constraints." [DoD-5000.29]
DoD Manual 5220.22-M (Paragraph 3.a) defines access as "the ability and opportunity to obtain knowledge of classified information. An individual, in fact, may have access to classified information by being in a place where such information is kept, if the security measures which are in force do not prevent him from gaining knowledge of the classified information." [DoD-5200.28]
The above mentioned Executive Order, Manual, Directives and Regulations clearly imply that a trusted computer system must assure that the classification labels associated with sensitive data cannot be arbitrarily changed, since this could permit individuals who lack the appropriate clearance to access classified information. Also implied is the requirement that a trusted computer system must control the flow of information so that data from a higher classification cannot be placed in a storage object of lower classification unless its "downgrading" has been authorized.
The term discretionary security refers to a computer system's ability to control information on an individual basis. It stems from the fact that even though an individual has all the formal clearances for access to specific classified information, each individual's access to information must be based on a demonstrated need-to-know. Because of this, it must be made clear that this requirement is not discretionary in a "take it or leave it" sense. The directives and regulations are explicit in stating that the need-to-know test must be satisfied before access can be granted to the classified information. The control objective for discretionary security is: "Security policies defined for systems that are used to process classified or other sensitive information must include provisions for the enforcement of discretionary access control rules. That is, they must include a consistent set of rules for controlling and limiting access based on identified individuals who have been determined to have a need-to-know for the information."
DoD Regulation 5200.1-R (Paragraph 7-100) In addition to excerpts already provided that touch on need-to- know, this section of the regulation stresses the need- to-know principle when it states "no person may have access to classified information unless . . . access is necessary for the performance of official duties." [Denning76]
Also, DoD Manual 5220.22-M (Section III 20.a) states that "an individual shall be permitted to have access to classified information only . . . when the contractor determines that access is necessary in the performance of tasks or services essential to the fulfillment of a contract or program, i.e., the individual has a need-to-know." [DoD-5200.28]