Discretionary Access Control (DAC) and Mandatory Access Control (MAC) are two common security access control mechanisms. Their core difference lies in the ownership of permission management. Below, we illustrate this with relatable examples and comparisons:
1. Discretionary Access Control (DAC)
Core Characteristics: “Who owns, who decides”, where the resource owner can freely allocate permissions.
Relatable Example: Suppose you have a diary (resource), you can decide:
- Allow your mom (User A) to read it, but not your dad (User B);
- Allow your best friend (User C) to browse it, but prohibit your colleague (User D) from accessing it.
Technical Scenarios:
- File System Permissions In Windows or Linux, the file owner can set “read/write/execute” permissions for other users or groups. For example: You created an Excel file and can allow only Colleague A to edit it, while only letting Colleague B view it.
- Social Media You can set your posts to be “public”, “friends only”, or “some people cannot see”.
Advantages: High flexibility, suitable for scenarios requiring personalized permission management.Disadvantages: Permissions may be abused (e.g., users sharing sensitive files with untrustworthy individuals).
2. Mandatory Access Control (MAC)
Core Characteristics: “The system decides”, where permissions are uniformly allocated by the system, and users cannot modify them.
Relatable Example: Suppose you are an employee of a company, and the company stipulates:
- All confidential documents (resources) can only be accessed by department managers and above (user labels);
- Ordinary employees (user labels) cannot open or modify the documents even if they see them.
Technical Scenarios:
- Military/Government Systems Documents are marked as “Top Secret”, “Secret”, or “Confidential”, and users access them based on security levels (e.g., “High”, “Medium”, “Low”). For example: A document marked as “Top Secret” can only be viewed by users with “High” permissions.
- Medical Systems Patient records are accessible only to authorized doctors based on privacy levels, while nurses or interns cannot view them.
Advantages: High security, preventing unauthorized access by internal personnel.Disadvantages: Low flexibility, high management costs (strict classification and labeling required).
3. Comparative Summary
| Characteristics | Discretionary Access Control (DAC) | Mandatory Access Control (MAC) |
|---|---|---|
| Permission Decider | Resource owner (user) | System (based on rules/labels) |
| Flexibility | High (freely allocatable) | Low (strictly limited) |
| Security | Lower (depends on user judgment) | High (system enforced) |
| Typical Scenarios | Personal files, social media, ordinary enterprise systems | Military, government, medical, financial, and other highly sensitive systems |
4. Hybrid Usage Scenarios
In reality, systems often combine the advantages of both:
- Linux Systems By default, use DAC (users can modify file permissions), but require root permissions for sensitive operations (similar to MAC).
- Enterprise Cloud Drives Ordinary files use DAC (users share freely), but confidential files use MAC (only specific departments can access).
Conclusion: DAC is like “the individual decides”, while MAC is like “the system sets the rules”. Choose or combine based on security needs.