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Chapter 14: System Protection and Security
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Goals of Protection
===================

Protection ensures that processes do not interfere with each other or with the OS.

Main goals:

- **Confidentiality** – Prevent unauthorized access to information.
- **Integrity** – Prevent unauthorized modification of data or resources.
- **Availability** – Ensure authorized users can access resources.
- **Safety** – Prevent actions that could cause harm or system failure.

Protection mechanisms define controlled access to resources such as files, memory, CPUs, and devices.


Domain of Protection
====================

A **domain** is a set of access rights. A process runs within a specific domain.

- **Access Rights:**  
  <object, permissions> pairs, such as ``(file1, read)``.

- **Static Domains:**  
  Domains assigned at process creation and do not change.

- **Dynamic Domains:**  
  Processes may switch domains (e.g., using system calls or capabilities).

Domain structures:

- **User Mode vs Kernel Mode**  
  Basic dual-domain separation.

- **Role-Based Domains**  
  Administrators, users, services.

- **Capability Lists and Tickets**  
  Unforgeable tokens that grant specific rights.


Access Matrix
=============

The **access matrix** formalizes protection by specifying:

- **Rows:** Subjects (users, processes, domains)
- **Columns:** Objects (files, devices, memory)
- **Entries:** Access rights (read, write, execute)

Example:

+----------+------------+------------+
|          | File A     | Printer    |
+==========+============+============+
| User 1   | read/write | use        |
+----------+------------+------------+
| User 2   | read       | -          |
+----------+------------+------------+

Implementation Techniques:

- **Access Control Lists (ACLs)**  
  Column-based; used by many OSes (Windows, Unix permissions).

- **Capability Lists**  
  Row-based; each subject holds a list of allowed accesses.

- **Lock-and-Key Mechanisms**  
  Objects have locks; domains hold keys to unlock them.


System and Network Security Threats
===================================

Systems face threats from internal and external adversaries.

Types of threats:

Malware
-------

- **Viruses** – Attach to executable files; require host.
- **Worms** – Self-replicating over networks.
- **Trojan Horses** – Malicious code disguised as legitimate software.
- **Ransomware** – Encrypts user data and demands payment.

Attack Techniques
-----------------

- **Phishing / Social Engineering**  
  Tricks users into exposing credentials.

- **Password Attacks**  
  Brute force, dictionary attacks, credential stuffing.

- **Privilege Escalation**  
  Exploiting vulnerabilities to gain higher permissions.

- **Man-in-the-Middle (MitM)**  
  Intercepting network communications.

- **Denial of Service (DoS/DDoS)**  
  Overloading systems to make them unavailable.

Network Security Measures
-------------------------

- **Encryption (TLS, HTTPS)**  
  Protects data in transit.

- **Firewalls and Packet Filters**  
  Restrict network traffic.

- **Intrusion Detection/Prevention Systems (IDS/IPS)**  
  Monitor for malicious patterns.

- **Authentication**  
  Passwords, multi-factor authentication, biometric systems.

- **Patching and Hardening**  
  Keeping systems updated and minimizing attack surface.