3.1 Security Models Explained

Key Concepts

Security models are frameworks that define how security policies are enforced within a system. They provide a structured approach to managing access control, ensuring that only authorized users can access specific resources. Key security models include the Bell-LaPadula Model, Biba Integrity Model, and Clark-Wilson Model.

Bell-LaPadula Model

The Bell-LaPadula Model is a security model used to enforce access control in systems with a hierarchical security policy. It ensures confidentiality by preventing unauthorized access to higher-level secure information. The model follows two main rules:

• No Read Up: Subjects (users) cannot read data from objects (files) with a higher security level.
• No Write Down: Subjects cannot write data to objects with a lower security level.

Example: In a military system, a soldier (subject) can read documents classified as "Confidential" but cannot read documents classified as "Top Secret." Similarly, a soldier cannot write "Top Secret" information into a "Confidential" document.

Biba Integrity Model

The Biba Integrity Model focuses on data integrity rather than confidentiality. It ensures that data is not modified by unauthorized users or processes. The model follows two main rules:

• No Read Down: Subjects cannot read data from objects with a lower integrity level.
• No Write Up: Subjects cannot write data to objects with a higher integrity level.

Example: In a financial system, an accountant (subject) can read and modify low-integrity data (e.g., expense reports) but cannot modify high-integrity data (e.g., financial statements). This prevents low-integrity data from contaminating high-integrity data.

Clark-Wilson Model

The Clark-Wilson Model is designed to ensure the integrity of transactions in a system. It enforces a strict separation of duties and ensures that transactions are well-formed and consistent. The model involves three main components:

• Constrained Data Items (CDIs): Data items that require integrity protection.
• Unconstrained Data Items (UDIs): Data items that do not require strict integrity protection.
• Transformation Procedures (TPs): Procedures that ensure data integrity by validating and transforming CDIs.

Example: In a banking system, a transaction to transfer funds (TP) must be validated and executed according to predefined rules. The account balances (CDIs) are protected from unauthorized modifications, ensuring that all transactions are consistent and accurate.

Conclusion

Security models provide a structured approach to managing access control and ensuring data integrity. The Bell-LaPadula Model focuses on confidentiality, the Biba Integrity Model on data integrity, and the Clark-Wilson Model on transaction integrity. Understanding these models helps in designing secure systems that protect sensitive information and maintain data consistency.