CISSP考试指南笔记：5.5 访问控制机制

An access control mechanism dictates how subjects access objects. It uses access control technologies and security mechanisms to enforce the rules and objectives of an access control model. There are five main types of access control models: discretionary, mandatory, role based, rule based, and attribute based.

These models are built into the core or the kernel of the different operating systems and possibly their supporting applications. Every operating system has a security kernel that enforces a reference monitor concept, which differs depending upon the type of access control model embedded into the system.

Discretionary Access Control

A system that uses discretionary access control (DAC) enables the owner of the resource to specify which subjects can access specific resources. This model is called discretionary because the control of access is based on the discretion of the owner.

In a DAC model, access is restricted based on the authorization granted to the users. This means users are allowed to specify what type of access can occur to the objects they own. If an organization is using a DAC model, the network administrator can allow resource owners to control who has access to their files.

DACs can be applied to both the directory tree structure and the files it contains.

Mandatory Access Control

In a mandatory access control (MAC) model, users do not have the discretion of determining who can access objects as in a DAC model. An operating system that is based upon a MAC model greatly reduces the amount of rights, permissions, and functionality a user has for security purposes.

The MAC model is much more structured and strict than the DAC model and is based on a security label system. Users are given a security clearance (secret, top secret, confidential, and so on), and data is classified in the same way. The clearance and classification data is stored in the security labels, which are bound to the specific subjects and objects.

DAC systems are discretionary and MAC systems are considered nondiscretionary because the users cannot make access decisions based upon their own discretion (choice).

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