Data Access Controls

Data access controls are established to control how subjects can access data, what they can access with it, and what they can do with it once accessed. Three primary types of access control are discussed in this section.

Discretionary Access Control (DAC)

The discretionary access control (DAC) model is so titled because access control is left to the owner's discretion. It can be thought of as similar to a peer-to-peer computer network. Each of the users is left in control. The owner is left to determine whether other users have access to files and resources. One significant problem with DAC is that its effectiveness is limited by user's skill and ability. A user who is inexperienced or simply doesn't care can easily grant full access to files or objects under his or her control. These are the two primary components of a DAC:

• File and data ownership All objects within a system must have an owner. Objects without an owner will be left unprotected.
• Access rights and permissions These control the access rights of an individual. Variation exists, but a basic access-control list checks read, write, or execute privileges.

Access rights are controlled through means of an access-control list (ACL). The ACL identifies users who have authorization to specific information. This is a dynamic model that allows data to be easily shared. A sample ACL is shown in Table 4.1. An ACL is a column within the access-control matrix displayed in Table 4.1. A subject's capabilities refer to a row within the matrix and reference what action can be taken.

Table 4.1. Sample Access-Control List

Subject	Object 1	Object 2	Object 3	Object 4
Mike	Full control	Full control	Full control	Full control
Jeff	Read	Read	Read write	No access
Clement	Read	Read write	No access	No access

 

Mandatory Access Control (MAC)

A MAC model is static and based on a predetermined list of access privileges; therefore, in a MAC-based system, access is determined by the system rather than the user. Figure 4.3 shows the differences between DAC and MAC. The MAC model is typically used by organizations that handle highly sensitive data (such as the DoD, NSA, CIA, and FBI). Systems based on the MAC model use sensitivity labels. Labels such as Top Secret, Secret, or Sensitive are assigned to objects. Objects are passive entities that provide data or information to subjects. A subject can be a user, system, program, or file. When a subject attempts to access an object, the label is examined for a match to the subject's level of clearance. If no match is found, access is denied. Important items to know about the MAC model include these:

Figure 4.3. Differences between DAC and MAC.

Objects are considered passive entities; subjects are considered active ones.

• It's considered a need-to-know system.
• It has more overhead than DAC.
• All users and resources are assigned a security label.

Object reuse refers to the reuse of media by individuals who might not have the need to know. This can happen when hard drives are shared, floppies are reused, or media is not properly wiped.

 

Role-Based Access Control (RBAC)

RBAC enables a user to have certain preestablished rights to objects. These rights are assigned to users based on their roles in the organization. The roles almost always map to the organization's structure. RBAC models are used extensively by banks and other organizations that have very defined roles. One profile might exist for tellers, while another exists for loan officers. Assigning access rights and privileges to a group rather than an individual reduces the burden on administration.

Other Types of Access Controls

Other types of access-control techniques include these:

• Content-dependent access control This model is based on the content of the resource. CDAC is primarily used to protect databases that contain potentially sensitive data.
• Lattice-based access control This MAC-based model functions by defining boundaries. For example, if you were cleared for secret access, you could read the level below, which is confidential.
• Rule-based access control Based on a specific set of rules much like a router ACL, this is considered a variation of the DAC model.