Different methodologies exist for defining and enforcing access control policies. The choice of model impacts management complexity, flexibility, and overall security posture.

3.3.1. Discretionary Access Control (DAC):

• Principle: The owner or creator of a resource has the "discretion" to define and modify access permissions for other users or groups to that resource. Permissions are typically assigned directly to individual users or groups.
• Characteristics:
• Owner-centric: Control over an object's permissions resides with its owner.
• Flexible and Decentralized: Owners can grant specific permissions to specific users, offering fine-grained control.
• Common Use: Widely implemented in most commercial operating systems (e.g., Windows NTFS permissions, Linux file permissions – rwx for owner, group, others). In a typical scenario, a user creates a file and then decides whether other users can read, write, or execute it.
• Advantages:
• Simple to understand and implement for individual users or small environments.
• Provides owners with direct control over their resources.
• Disadvantages:
• Lack of Centralized Control: Security policy enforcement can be inconsistent across a large organization, as individual users dictate access.
• "Trojan Horse" Vulnerability: A malicious program (trojan horse) running with a user's legitimate privileges can perform unauthorized actions on behalf of that user, including granting itself permissions to other objects that the user owns.
• Complexity at Scale: Managing permissions manually for thousands of users and millions of files becomes unwieldy and error-prone in large enterprises.
• Risk of Over-permissioning: Users might inadvertently or negligently grant more permissions than necessary, violating the principle of least privilege.

3.3.2. Mandatory Access Control (MAC):

• Principle: Access decisions are not left to the discretion of resource owners but are strictly enforced by a central authority or security kernel, based on predefined system-wide security labels or clearances. Both subjects (users, processes) and objects (files, programs) are assigned sensitivity labels.
• Characteristics:
• System-centric/Centralized: The operating system's security kernel makes all access decisions based on security labels and rules. Owners have no discretion.
• High Assurance: Provides a very high level of security and information separation.
• Common Use: Primarily used in highly secure environments (e.g., military, intelligence agencies, government) where strict confidentiality or integrity is paramount.
• Models:
  • Bell-LaPadula Model (Confidentiality): Focuses on preventing information leakage. Rules: "No read up" and "No write down."
  • Biba Model (Integrity): Focuses on preventing data corruption. Rules: "No read down" and "No write up."
• Advantages:
• Extremely strong security guarantees against unauthorized disclosure or alteration.
• Enforces a consistent, system-wide security policy.
• Disadvantages:
• High Complexity and Administrative Overhead: Implementing and managing MAC systems is very complex, requiring extensive initial setup and ongoing management of security labels.
• Low Flexibility: Can be rigid and less adaptable to dynamic or diverse access needs of a typical enterprise.
• Usability Challenges: Can hinder legitimate work by over-restricting access, potentially leading to users seeking workarounds.

3.3.3. Role-Based Access Control (RBAC):

• Principle: Permissions are organized around roles, not directly assigned to individual users. Users are assigned one or more roles, and they inherit all permissions associated with those roles. This separates the management of users from the management of permissions.
• Characteristics:
• Role-centric: The central concept is the "role" (e.g., "System Administrator," "HR Manager," "Guest User," "Database Analyst").
• Indirect Permissions: Permissions are granted to roles, and users are assigned to roles.
• Hierarchy/Inheritance: Roles can often be organized hierarchically, where a higher-level role inherits permissions from lower-level roles.
• Common Use: The most widely adopted access control model in enterprise environments due to its balance of security and manageability.
• Advantages:
• Simplified Management and Scalability: Easier to manage access for large numbers of users. When a new employee joins, they are simply assigned pre-defined roles.
• Improved Enforcement of Least Privilege: Encourages the creation of roles with precisely the minimum necessary permissions for specific job functions.
• Easier Auditing: Auditing access rights becomes simpler as you can inspect permissions at the role level.
• Reduced Error Rate: Reduces the chance of human error in assigning permissions compared to managing them individually.
• Disadvantages:
• Initial setup can be complex, requiring careful analysis of organizational structure and job functions to define appropriate roles.
• If roles are poorly defined or too broad, they can still lead to over-permissioning.