CertiGuide to Security+  9  Chapter 1:  General Security Concepts (Domain 1.0; 30%)       9  1.1  Access Control

1.1  Access Control 1 1.1.2  Discretionary Access Control (DAC)

Mandatory Access Control (MAC) is military-strength access control. In the absence of a permission that specifically allows you access, you are not getting in. Every thing in the system is an object and every object gets a classification label, which usually represents the sensitivity of the object, such as “top secret” or “confidential”. Individual users, called subjects, are also assigned a privilege level, called a clearance. To determine whether or not a given individual can access a certain object, the object’s classification level and the user’s clearance level are compared. There is an established hierarchy to the labels (or levels), such that anyone authorized to see “top secret” information can also view “secret” and “general access” information since those are less sensitive, but someone authorized only to view “general access” information can’t necessarily see the more sensitive “top secret” information.

The Bell-LaPadula formal model of access control uses mandatory access control. It is based on several properties, including:

• star property (or * property), also called the containment level, which states that an untrustworthy user can only write (append information) to objects whose security level is greater than or equal to their own (to make sure that someone with a high clearance level doesn’t accidentally share sensitive information with someone having a lower clearance level – i.e., it prevents “information leakage”)
  
  
• simple property, which states that a user can read data only if its security level is as sensitive as, or less sensitive than, their clearance level (think about a 4-star general being entitled to see more data than a 1-star general)
  
  
• tranquility property, which states that the security level of an object cannot be changed while it is in use by the computer system (this sidesteps the problem of what to do with users actively using an object who are no longer permitted access when the object’s security level changes)

Another MAC-based model is the Lattice-based access control model. It shares with the Bell-LaPadula model the idea that objects and users are each given a hierarchical security level label, and that you determine whether or not a user has access to an object, by comparing their labels. As with Bell-LaPadula, if the user’s clearance level is at or above the classification level of the object, access is permitted.

1.1  Access Control 1 1.1.2  Discretionary Access Control (DAC)