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This chapter is from the book

This chapter is from the book

Documents and Guidelines

The documents and guidelines discussed in the following sections were developed to help evaluate and establish system assurance. These items are important to the CISSP candidate because they provide a level of trust and assurance that these systems will operate in a given and predictable manner. A trusted system has undergone testing and validation to a specific standard. Assurance is the freedom of doubt and a level of confidence that a system will perform as required every time it is used. This system can be used by all. When a developer prepares to sell a system, he must have a way to measure the system’s features and abilities. The buyer, when preparing to make a purchase, must have a way to measure the system’s effectiveness and benchmark its abilities. The following documents and guidelines facilitate these needs.

The Rainbow Series

The rainbow series is aptly named because each book in the series has a label of a different color. This 6-foot-tall stack of books was developed by the National Computer Security Center (NCSC), an organization that is part of the National Security Agency (NSA). These guidelines were developed for the Trusted Product Evaluation Program (TPEP), which tests commercial products against a comprehensive set of security-related criteria. The first of these books was released in 1983 and is known as Trusted Computer System Evaluation Criteria (TCSEC) or the Orange Book. Because it addresses only standalone systems, other volumes were developed to increase the level of system assurance.

The Orange Book: Trusted Computer System Evaluation Criteria

The Orange Book’s official name is the Trusted Computer System Evaluation Criteria. As noted, it was developed to evaluate standalone systems. Its basis of measurement is confidentiality, so it is similar to the Bell-LaPadula model. It is designed to rate systems and place them into one of four categories:

  • A—Verified protection. An A-rated system is the highest security division.
  • B—Mandatory security. A B-rated system has mandatory protection of the TCB.
  • C—Discretionary protection. A C-rated system provides discretionary protection of the TCB.
  • D—Minimal protection. A D-rated system fails to meet any of the standards of A, B, or C and basically has no security controls.

The Orange Book not only rates systems into one of four categories, but each category is also broken down further. For each of these categories, a higher number indicates a more secure system, as noted in the following:

  • A is the highest security division. An A1 rating means that the system has verified protection and supports mandatory access control (MAC).

    • A1 is the highest supported rating. Systems rated as such must meet formal methods and proof of integrity of TCB. An A1 system must not only be developed under strict guidelines but must also be installed and delivered securely. Examples of A1 systems include the Gemini Trusted Network Processor and the Honeywell SCOMP.
  • B is considered a mandatory protection design. Just as with an A-rated system, those that obtain a B rating must support MAC.

    • B1 (labeled security protection) systems require sensitivity labels for all subjects and storage objects. Examples of B1-rated systems include the Cray Research Trusted Unicos 8.0 and the Digital SEVMS.
    • For a B2 (structured protection) rating, the system must meet the requirements of B1 and support hierarchical device labels, trusted path communications between user and system, and covert storage analysis. An example of a B2 system is the Honeywell Multics.
    • Systems rated as B3 (security domains) must meet B2 standards and support trusted path access and authentication, automatic security analysis, and trusted recovery. B3 systems must address covert timing vulnerabilities. A B3 system must not only support security controls during operation but also be secure during startup. An example of a B3-rated system is the Federal XTS-300.
  • C is considered a discretionary protection rating. C-rated systems support discretionary access control (DAC).

    • Systems rated at C1 (discretionary security protection) don’t need to distinguish between individual users and types of access.
    • C2 (controlled access protection) systems must meet C1 requirements plus must distinguish between individual users and types of access by means of strict login controls. C2 systems must also support object reuse protection. A C2 rating is common; products such as Windows NT and Novell NetWare 4.11 have a C2 rating.
  • Any system that does not comply with any of the other categories or that fails to receive a higher classification is rated as a D-level (minimal protection) system. MS-DOS is a D-rated system.

Although the Orange Book is no longer considered current, it was one of the first standards. It is reasonable to expect that the exam might ask you about Orange Book levels and functions at each level. Listed in Table 5.4 are important notes to keep in mind about Orange Book levels.

Table 5.4. Orange Book Levels


Items to Remember


Built, installed, and delivered in a secure manner


Security labels (MAC)


Security labels and verification of no covert channels (MAC


Security labels, verification of no covert channels, and must stay secure during startup (MAC)


Weak protection mechanisms (DAC


Strict login procedures (DAC)


Failed or was not tested

The Red Book: Trusted Network Interpretation

The Red Book’s official name is the Trusted Network Interpretation (TNI). The purpose of the TNI is to examine security for network and network components. Whereas the Orange Book addresses only confidentiality, the Red Book examines integrity and availability. It also is tasked with examining the operation of networked devices. Three areas of reviews of the Red Book include

  • DoS prevention—Management and continuity of operations.
  • Compromise protection—Data and traffic confidentiality, selective routing.
  • Communications integrity—Authentication, integrity, and nonrepudiation.

Information Technology Security Evaluation Criteria

ITSEC is a European standard developed in the 1980s to evaluate confidentiality, integrity, and availability of an entire system. ITSEC was unique in that it was the first standard to unify markets and bring all of Europe under one set of guidelines. ITSEC designates the target system as the Target of Evaluation (TOE). The evaluation is actually divided into two parts: One part evaluates functionality and the other evaluates assurance. There are 10 functionality (F) classes and 7 assurance (E) classes. Assurance classes rate the effectiveness and correctness of a system. Table 5.5 shows these ratings and how they correspond to the TCSEC ratings.

Table 5.5. ITSEC Functionality Ratings and Comparison to TCSEC

(F) Class

(E) Class

TCSEC Rating























TOEs with high integrity requirements


TOEs with high availability requirements


TOEs with high integrity requirements during data communications


TOEs with high confidentiality requirements during data communications


Networks with high confidentiality and integrity requirements

Common Criteria

With all the standards we have discussed, it is easy to see how someone might have a hard time determining which one is the right choice. The International Standards Organization (ISO) had these same thoughts; therefore, it decided that because of the various standards and ratings that existed, there should be a single global standard. Figure 5.7 illustrates the development of Common Criteria.

Figure 5.7

Figure 5.7. Common Criteria development.

In 1997, the ISO released the Common Criteria (ISO 15408), which is an amalgamated version of TCSEC, ITSEC, and the CTCPEC. Common Criteria is designed around TCB entities. These entities include physical and logical controls, startup and recovery, reference mediation, and privileged states. Common Criteria categorizes assurance into one of seven increasingly strict levels of assurance. These are referred to as Evaluation Assurance Levels (EALs). EALs provide a specific level of confidence in the security functions of the system being analyzed. The system being analyzed and tested is known as the Target of Evaluation (TOE), which is just another name for the system being subjected to the security evaluation. A description of each of the seven levels of assurance follows:

  • EAL 0—Inadequate assurance
  • EAL 1—Functionality tested
  • EAL 2—Structurally tested
  • EAL 3—Methodically checked and tested
  • EAL 4—Methodically designed, tested, and reviewed
  • EAL 5—Semiformally designed and tested
  • EAL 6—Semiformally verified designed and tested
  • EAL 7—Formally verified designed and tested

Common Criteria defines two types of security requirements: functional and assurance. Functional requirements define what a product or system does. They also define the security capabilities of a product. The assurance requirements and specifications to be used as the basis for evaluation are known as the Security Target (ST). A protection profile defines the system and its controls. The protection profile is divided into the following five sections:

  • Rationale
  • Evaluation assurance requirements
  • Descriptive elements
  • Functional requirements
  • Development assurance requirements

Assurance requirements define how well a product is built. Assurance requirements give confidence in the product and show the correctness of its implementation.

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