The information system shall implement a reference monitor for organization-defined access control policies. Which of the following is not a mandatory property of reference monitor?
A. Tamperproof
B. Small enough
C. High cohesion
D. Always invoked
Kindly be reminded that the suggested answer is for your reference only. It doesn’t matter whether you have the right or wrong answer. What really matters is your reasoning process and justifications.
My suggested answer is C. High cohesion.
The reference monitor concept was first introduced in the well-known Anderson report by James P. Anderson & Co. in 1972 and then adopted in the TCSEC n 1983. It is also specified as one of the baseline controls in the control framework, NIST SP 800-53 R5.
The following is an excerpt from NIST SP 800-53 R5.
AC-25 REFERENCE MONITOR
Control: Implement a reference monitor for [Assignment: organization-defined access control policies] that is tamperproof, always invoked, and small enough to be subject to analysis and testing, the completeness of which can be assured.
Discussion:
A reference monitor is a set of design requirements on a reference validation mechanism that, as a key component of an operating system, enforces an access control policy over all subjects and objects.
A reference validation mechanism is always invoked, tamper-proof, and small enough to be subject to analysis and tests, the completeness of which can be assured (i.e., verifiable). Information is represented internally within systems using abstractions known as data structures. Internal data structures can represent different types of entities, both active and passive. Active entities, also known as subjects, are associated with individuals, devices, or processes acting on behalf of individuals. Passive entities, also known as objects, are associated with data structures, such as records, buffers, communications ports, tables, files, and inter-process pipes.
Reference monitors enforce access control policies that restrict access to objects based on the identity of subjects or groups to which the subjects belong. The system enforces the access control policy based on the rule set established by the policy.
The tamper-proof property of the reference monitor prevents determined adversaries from compromising the functioning of the reference validation mechanism. The always invoked property prevents adversaries from bypassing the mechanism and violating the security policy. The smallness property helps to ensure completeness in the analysis and testing of the mechanism to detect any weaknesses or deficiencies (i.e., latent flaws) that would prevent the enforcement of the security policy.
Related Controls: AC-3, AC-16, SA-8, SA-17, SC-3, SC-11, SC-39, SI-13.
Control Enhancements: None.
References: None.
TCSEC (Orange Book)
High Cohesion
In computer programming, cohesion refers to the degree to which the elements inside a module belong together. In one sense, it is a measure of the strength of relationship between the methods and data of a class and some unifying purpose or concept served by that class. In another sense, it is a measure of the strength of relationship between the class’s methods and data themselves.
Cohesion is an ordinal type of measurement and is usually described as “high cohesion” or “low cohesion”. Modules with high cohesion tend to be preferable, because high cohesion is associated with several desirable traits of software including robustness, reliability, reusability, and understandability. In contrast, low cohesion is associated with undesirable traits such as being difficult to maintain, test, reuse, or even understand.
Cohesion is often contrasted with coupling, a different concept. High cohesion often correlates with loose coupling, and vice versa. The software metrics of coupling and cohesion were invented by Larry Constantine in the late 1960s as part of Structured Design, based on characteristics of “good” programming practices that reduced maintenance and modification costs. Structured Design, cohesion and coupling were published in the article Stevens, Myers & Constantine (1974) and the book Yourdon & Constantine (1979); the latter two subsequently became standard terms in software engineering.
Source: Wikipedia
Reference
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資訊系統應為組織定義的存取控制政策實現一個參考監視器(reference monitor)。 以下哪個不是參考監視器的必要屬性？
A. 防篡改 (Tamperproof)
B. 足夠小 (Small enough)
C. 高凝聚力 (High cohesion)
D. 總是被調用 (Always invoked)