Security models help design secure systems by enforcing Confidentiality, Integrity, and Availability (CIA). Here, we explore three foundational models:
1️⃣ Bell-LaPadula Model (Confidentiality-Focused)
- Purpose: Ensures confidentiality (protects against unauthorized reading of sensitive information).
- Rules:
- Simple Security Property ("No Read Up"): A lower-level subject cannot read higher-level information.
- Star Security Property ("No Write Down"): A higher-level subject cannot write to a lower-level object.
- Discretionary Security Property: Uses an access matrix to define permissions.
- Summary: Write up, read down → Prevents data leakage from high-security levels to low-security levels.
- Limitation: Not designed for file-sharing environments.
Example:
- A government employee with SECRET clearance cannot read data labeled TOP SECRET (No Read Up).
- A TOP SECRET officer cannot write to a CONFIDENTIAL document (No Write Down).
2️⃣ Biba Integrity Model (Integrity-Focused)
- Purpose: Ensures integrity (prevents unauthorized modification of data).
- Rules:
- Simple Integrity Property ("No Read Down"): A subject cannot read from a lower integrity level.
- Star Integrity Property ("No Write Up"): A subject cannot write to a higher integrity level.
- Summary: Read up, write down → Prevents lower-trust users from corrupting higher-trust data.
- Limitation: Does not address internal threats (insider attacks).
Example:
- A financial system accountant cannot read unverified transaction logs (No Read Down).
- A low-trust user cannot write to a high-integrity transaction record (No Write Up).
3️⃣ Clark-Wilson Model (Integrity with Process Control)
- Purpose: Focuses on integrity by enforcing controlled modifications using well-defined procedures.
- Key Concepts:
- Constrained Data Item (CDI): Data requiring integrity protection (e.g., financial transactions).
- Unconstrained Data Item (UDI): General user/system input (e.g., user entries).
- Transformation Procedures (TPs): Securely modify CDIs (e.g., bank transaction processing).
- Integrity Verification Procedures (IVPs): Ensure CDI integrity (e.g., auditing functions).
- Summary: Integrity is maintained by restricting direct data modification—only trusted programs can alter critical data.
Example:
- A bank transaction system ensures that only authorized transactions modify account balances.
- Audit logs (IVPs) verify all changes to prevent fraud.
Other Security Models
- Brewer and Nash Model: Prevents conflicts of interest in financial/trading firms.
- Goguen-Meseguer Model: Uses non-interference to enforce strict security controls.
- Sutherland Model: Focuses on preventing information flow violations.
- Graham-Denning Model: Defines secure access controls for objects.
- Harrison-Ruzzo-Ullman Model: Extends access control lists for dynamic security.
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