Video - Session 4

### Overview This session, part of a 13-class security certification preparation course (roughly one-third complete at class four), covers fundamental security engineering concepts, classic security models, evaluation criteria, and secure hardware and operating system architectures. The instructor emphasizes that while many historical evaluation frameworks and formal security models are rarely implemented directly in everyday governance or operations, understanding their underlying concepts and rules is essential for passing the certification exam.

### Key Topics The session opens with a review quiz from the prior class covering data classification, memory types (e.g., SRAM vs. DRAM, EEPROM), disposal methods (degaussing, solid-state drive sanitization), and roles like data owners and custodians. The instructor then transitions into the core security engineering material: - **Access Control Fundamentals:** Distinctions between Discretionary Access Control (DAC), Mandatory Access Control (MAC), and Rule-based Access Control. - **Formal Security Models:** State Machine model, Bell-LaPadula (confidentiality-focused), Biba (integrity-focused), Clark-Wilson, Brewer-Nash (Chinese Wall), Non-interference, Take-Grant, Access Control Matrix, Zachman Framework, Graham-Denning, and Harrison-Ruzzo-Ullman (HRU). - **Modes of Operation:** Dedicated, System High, Compartmented, and Multi-level security modes. - **Evaluation Criteria:** Historical frameworks including TCSEC (Orange Book), TNI (Red Book), ITSEC, and the Common Criteria (ISO/IEC 15408) with Evaluation Assurance Levels (EAL1 through EAL7). - **System Architecture & Hardware Security:** Layering, rings of protection (Ring 0 through Ring 3, plus hypervisors at Ring -1), kernel modes (monolithic vs. microkernel), CPU operations (fetch, decode, execute, store), multiprocessing/multitasking, memory protection, BIOS boot processes, and Trusted Platform Modules (TPM).

### Technical Details - **Security Models:** The discussion contrasts Bell-LaPadula and Biba. Bell-LaPadula enforces confidentiality using the Simple Security Property ("no read up") and the Star (*) Security Property ("no write down"), alongside tranquility properties. Conversely, Biba protects data integrity using the Simple Integrity Axiom ("no read down") and the Star (*) Integrity Axiom ("no write up"). Clark-Wilson focuses on separation of duties and well-formed transactions utilizing transformation procedures (TPs) and constrained data items (CDIs). Brewer-Nash mitigates conflicts of interest using dynamic boundaries (Chinese Wall). The Non-interference model prevents high-level activity from affecting low-level activity, defending against covert channel leakage (such as inferences drawn from shared temp directories or page files). - **Operating Modes:** The session contrasts dedicated systems (single classification, all users require clearance, need-to-know, and formal approval) against system high, compartmented, and multi-level operating modes (which rely on the reference monitor to arbitrate access across diverse classifications). - **Hardware & Kernel Architecture:** Protection rings separate privilege levels: Ring 0 (kernel/reference monitor), Ring 1 (OS services), Ring 2 (device drivers), and Ring 3 (user applications). The reference monitor within the kernel mediates all access between subjects and objects, remains tamper-proof, and consults authorization databases while producing audit trails. Hardware mechanisms discussed include CPU clock instruction cycles (fetch, decode, execute, store), pipelining, symmetric vs. asymmetric multiprocessing, process isolation, virtual memory paging/swapping, and the boot sequence from BIOS/MBR into the kernel. TPM chips are noted for providing hardware-based cryptographic offloading and boot/platform integrity verification.

### Takeaways The class concludes with practical study advice for the exam. The instructor and co-host recommend reading the study materials multiple times to move from initial exposure to conceptual understanding and final mastery. They emphasize extensive practice testing (such as 250-question mock exams) to build stamina and identify weak domains before test day.