Information Security

Pass path: Learn the CIA triad, Saltzer & Schroeder design principles, and DAC vs RBAC vs ABAC. Top path: Evaluate attack trees for enterprise threats, analyze Bell-LaPadula vs Biba formal axioms, and design Attribute-Based Access Control policies.

Part 1: Core Concepts (2 Marks)

★ The CIA Triad: Confidentiality (concealing information from unauthorized parties), Integrity (protecting data from unauthorized modification or deletion), and Availability (ensuring legitimate users have timely and dependable access to assets). ★ Discretionary (DAC) vs Role-Based Access Control (RBAC): In DAC, the individual file owner controls permissions; in RBAC, permissions are assigned to organizational job roles, and users are assigned to roles, centralizing enterprise governance. ★ Attack Surface vs Attack Tree: An attack surface is the total reachable set of entry points and interfaces exposed to an adversary; an attack tree is a conceptual branching diagram modeling potential attack paths toward an adversarial goal.

Part 2: Structural Frameworks (10 Marks)

Computer Security Fundamentals, Access Control Architectures, and Formal Models

• Saltzer & Schroeder Security Design Principles:
  1. Economy of Mechanism: Keep security designs as simple and small as possible (fewer code paths to verify).
  2. Fail-Safe Defaults: Default access should be “Deny All”; permissions explicitly granted.
  3. Complete Mediation: Every access request must be checked against access rules on every transaction.
  4. Open Design: Security must not rely on secrecy of implementation (Kerckhoffs’s Principle).
  5. Separation of Privilege: Multiple conditions required to unlock critical access (e.g. dual authorization).
  6. Least Privilege: Grant the absolute minimal permissions required to perform legitimate tasks.

CIA Security Triad Diagram

• Formal Security Models Comparison:
  • Bell-LaPadula (Confidentiality Model):
    • Simple Security Property (ss-property): “No Read Up” (a subject at clearance level $L$ cannot read an object at level $> L$).
    • Star-Property ($\star$-property): “No Write Down” (a subject cannot write to an object at level $< L$, preventing leaks).
  • Biba Model (Integrity Model):
    • Simple Integrity Property: “No Read Down” (cannot read data from lower integrity levels).
    • Star-Integrity Property: “No Write Up” (cannot write tainted data to higher integrity systems).

Part 3: Distinction Tables

Part 4: Worked Problems & Exam Traps

• Easy: What security property does ransomware attack?
  • Answer: Availability (by encrypting files and locking out owners) and Confidentiality (via exfiltration extortion).
• Exam-level: Contrast the Bell-LaPadula model with the Biba integrity model.
  • Answer: Bell-LaPadula is designed to preserve Confidentiality in multi-level military systems by enforcing “No Read Up, No Write Down” rules to prevent unauthorized disclosure. Biba is designed to preserve Integrity in commercial systems by enforcing “No Read Down, No Write Up” rules to prevent unauthorized corruption from untrusted inputs.
• Twist variant: Does a firewall reduce the attack surface of a corporate internal network?
  • Answer: Yes. By blocking unauthorized incoming ports and filtering protocols, it eliminates reachable network entry points, directly shrinking the exterior attack surface.

Students lose marks here because they invert the axioms of Bell-LaPadula and Biba, claiming Bell-LaPadula permits writing down or that Biba prevents unauthorized disclosure instead of corruption.