Discretionary Access Control (DAC) is a type of access control system that provides an access policy determined by the owner of the data or resource. The owner has the discretion to grant or deny access to other users or processes.
The Genesis and Evolution of Discretionary Access Control
The concept of Discretionary Access Control dates back to the earliest days of shared computing systems, specifically in the Multics (Multiplexed Information and Computing Service) system developed in the 1960s. The Multics system included a rudimentary form of DAC, which later became the inspiration for modern access control systems. DAC became a formalized concept with the release of the United States Department of Defense’s “Orange Book” in the 1980s, which defined several levels of security controls, including DAC.
Expanding the Understanding of Discretionary Access Control
Discretionary Access Control is based on the principles of discretionary privileges. This means that the individual or entity owning the data or resource has the power to decide who can access that data or resource. This control can extend to both read and write permissions. Under DAC, an access control list (ACL) is maintained, which specifies the kind of access a user or a user group has over a particular resource.
The Internal Structure and Functioning of Discretionary Access Control
The DAC model primarily relies on two key components: Access Control Lists (ACLs) and capability tables. The ACLs are associated with each resource or object and contain a list of subjects (users or processes) along with their granted permissions. On the other hand, capability tables maintain a list of objects that a particular subject can access.
When a request for access is made, the DAC system checks the ACL or the capability table to determine if the requester is allowed to access the resource. If the ACL or capability table grants access, the request is approved. Otherwise, it’s denied.
Key Features of Discretionary Access Control
- Owner-Determined Access: The owner of the data or resource determines who can access it.
- Access Control Lists: An ACL determines what kind of access each user or user group has.
- Capability Tables: These tables list the resources a user or user group can access.
- Flexibility: Owners can easily change permissions as required.
- Transitive Access Control: If a user has access to a resource, they can potentially grant access to another user.
Types of Discretionary Access Control
While DAC can be implemented in various ways, the two most common approaches are ACLs and capability lists.
| Approach | Description |
|---|---|
| Access Control Lists (ACLs) | ACLs are tied to an object (a file, for example) and specify which users can access the object and what operations they can perform on it. |
| Capability Lists | Capability lists are tied to a user and specify what objects the user can access and what operations they can perform on those objects. |
Application, Challenges, and Solutions of Discretionary Access Control
DAC is widely used in most operating systems and file systems, such as Windows and UNIX, allowing users to share files and resources with chosen individuals or groups.
One major challenge with DAC is the “confused deputy problem,” where a program can unintentionally leak access rights. For example, a user might trick a program with more access rights into performing an action on their behalf. This problem can be mitigated by careful programming and proper use of system privileges.
Another problem is the potential for rapid, uncontrolled propagation of access rights, as users with access to a resource can potentially grant that access to others. This can be addressed through proper education and training, as well as system-level controls to limit such propagation.
Comparison of Discretionary Access Control with Similar Terms
| Term | Description |
|---|---|
| Discretionary Access Control (DAC) | Owners have total control over their data and resources. |
| Mandatory Access Control (MAC) | A centralized policy restricts access based on classification levels. |
| Role-Based Access Control (RBAC) | Access is determined by the user’s role within the organization. |
The future of DAC is likely to evolve with the increasing popularity of cloud-based platforms and the Internet of Things (IoT) devices. Fine-grained access control, which provides more detailed control over permissions, is expected to become more commonplace. Additionally, as machine learning and AI technologies advance, we may see DAC systems that can learn and adapt to changing access needs.
Proxy Servers and Discretionary Access Control
Proxy servers can use DAC principles to control access to web resources. For example, a company might set up a proxy server that checks the user’s identity and role before allowing access to certain websites or web-based services. This ensures that only authorized personnel can access specific online resources, providing an additional layer of security.
Related Links
- Computer Security: Art and Science by Matt Bishop: A comprehensive resource on computer security, including access control.
- Understanding and Using Discretionary Access Control: An article by CSO, exploring DAC in detail.
- NIST Special Publication 800-12: The U.S. National Institute of Standards and Technology’s guide to computer security, including a discussion on DAC.
- Access Control Models: A detailed guide to various access control models by O’Reilly Media.
- DAC, MAC, and RBAC: A scientific article comparing DAC, MAC, and RBAC models.
