Documents and Guidelines | System Architecture and Models

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.

The Rainbow Series

The rainbow series is aptly named because each book in the series has a different color of label. 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 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 (TCSEC). 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 Canadians have their own version of the Orange Book, known as The Canadian Trusted Computer Product Evaluation Criteria (CTCPEC). It is seen as a more flexible version of TCSEC.

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. 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 channel 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. 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.
  
  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.

The CISSP exam will not expect you to know what systems meet the various Orange Book ratings; however, it will expect you to know where MAC and DAC are applied.

The Red Book: Trusted Network Interpretation

The Red Book's official name is the Trusted Network Interpretation. Its purpose is to address the deficiencies of the Orange Book. Although the Orange Book addresses only confidentiality, the Red Book examines integrity and availability. It also is tasked with examining the operation of networked devices.

Information Technology Security Evaluation Criteria (ITSEC)

ITSEC is a European standard that was developed in the 1980s to evaluate confidentiality, integrity, and availability of an entire system. 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 the system. Table 5.1 shows these ratings and how they correspond to the TCSEC ratings.

Table 5.1. ITSEC Functionality Ratings and Comparison to TCSEC
(F) Class	(E) Class	TCSEC Rating
NA	E0	D
F1	E1	C1
F2	E2	C2
F3	E3	B1
F4	E4	B2
F5	E5	B3
F5	E6	A1
F6		TOEs with high integrity requirements
F7		TOEs with high availability requirements
F8		TOEs with high integrity requirements during data communications
F9		TOEs with high confidentiality requirements during data communications
F10		Networks with high confidentiality and integrity requirements

Common Criteria

With all the standards we have discussed, it would be 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, they decided that because of the various standards and ratings that existed, there should be a single global standard.

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 increas ingly strict levels of assurance. These are referred to as Evaluation Assurance Levels (EAL). 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 that is being subjected to the security evaluation. The assurance require ments and specifications to be used as the basis for evaluation are known as the Security Target (ST). 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 the product. Assurance requirements define how well the product is built. Assurance requirements give confidence in the product and show the correctness of its implementation.

The Common Criteria seven levels of assurance and its two security requirements are required test knowledge.

British Standard 7799

The BS 7799 was developed in England to be used as a standard method to measure risk. Because the document found such a wide audience and was adopted by businesses and organizations, it evolved into ISO 17799 in December 2000. This is a comprehensive standard in its coverage of security issues and is divided into 10 sections: