🔒Cybersecurity and Cryptography Unit 5 – OS Security and Access Control

Core Concepts

• Operating system security focuses on protecting the OS from unauthorized access, misuse, and exploitation
• Access control is a fundamental aspect of OS security that regulates who can access system resources and how they can be used
• Authentication verifies the identity of users or processes seeking access to the system (username and password, biometric data, smart cards)
• Authorization determines the permissions and privileges granted to authenticated users or processes
  • Principle of least privilege limits access rights to the minimum necessary for users to perform their tasks
• Security policies define the rules and guidelines for maintaining the security of an operating system
  • Policies cover areas such as access control, user management, network security, and incident response
• Threat modeling identifies potential security risks and vulnerabilities in an operating system
  • Helps prioritize security measures and allocate resources effectively
• Security auditing involves monitoring and logging system activities to detect and investigate security incidents
  • Audit trails provide a record of user actions, system events, and security-related information

OS Security Fundamentals

• Operating system security aims to protect the confidentiality, integrity, and availability of system resources and data
• Security features are built into modern operating systems to prevent unauthorized access and misuse
  • Examples include user authentication, access control lists (ACLs), and encryption
• Kernel-level security mechanisms enforce security policies and protect critical system components
  • The kernel is the core of the operating system and has the highest level of privilege
• Process isolation techniques prevent unauthorized interaction between processes and limit the impact of security breaches
  • Each process runs in its own memory space and cannot directly access the memory of other processes
• Address space layout randomization (ASLR) makes it harder for attackers to exploit memory-related vulnerabilities
• Secure boot ensures that only trusted and verified operating system components are loaded during the boot process
• Regular software updates and patches are essential to fix security vulnerabilities and protect against emerging threats

Access Control Models

• Access control models define the rules and policies for granting or restricting access to system resources
• Discretionary Access Control (DAC) allows resource owners to determine who can access their resources and how they can be accessed
  • Access rights are assigned to users or groups at the discretion of the owner
  • Implemented using access control lists (ACLs) or permission bits (read, write, execute)
• Mandatory Access Control (MAC) enforces system-wide security policies that cannot be overridden by users
  • Access rights are determined by security labels assigned to subjects (users or processes) and objects (files, directories)
  • Commonly used in high-security environments (military, government)
• Role-Based Access Control (RBAC) grants access based on the roles and responsibilities of users within an organization
  • Users are assigned to roles, and permissions are associated with each role
  • Simplifies access management and reduces the risk of unauthorized access
• Attribute-Based Access Control (ABAC) uses attributes of subjects, objects, and the environment to make access decisions
  • Attributes can include user credentials, object metadata, time of day, location, or security clearance
• Rule-Based Access Control defines specific rules and conditions that must be met for access to be granted
  • Rules can be based on user attributes, system state, or external factors

Authentication Methods

• Authentication verifies the identity of users or processes before granting access to system resources
• Password-based authentication is the most common method, where users provide a username and password to log in
  • Passwords should be strong, unique, and regularly updated to maintain security
  • Password policies enforce requirements such as minimum length, complexity, and expiration
• Multi-factor authentication (MFA) combines two or more authentication factors to enhance security
  • Factors can include something you know (password), something you have (smart card, token), or something you are (biometric data)
• Biometric authentication uses unique physical characteristics to verify identity (fingerprints, facial recognition, iris scans)
  • Provides a high level of assurance but requires specialized hardware and can raise privacy concerns
• Certificate-based authentication uses digital certificates to prove the identity of users or devices
  • Certificates are issued by trusted certificate authorities (CAs) and contain information about the owner's identity
• Single sign-on (SSO) allows users to authenticate once and access multiple systems or applications without re-entering credentials
  • Reduces the burden of managing multiple passwords and improves user experience
• Risk-based authentication dynamically adjusts authentication requirements based on the assessed risk level of a user or transaction
  • May require additional verification steps for high-risk activities (large financial transactions, access from unfamiliar locations)

Authorization Techniques

• Authorization determines the permissions and privileges granted to authenticated users or processes
• Access control lists (ACLs) specify the permissions associated with an object (file, directory) for different users or groups
  • Each entry in an ACL defines the access rights (read, write, execute) for a specific user or group
• Role-based authorization assigns permissions to roles rather than individual users
  • Users acquire permissions based on the roles they are assigned to
  • Simplifies permission management and ensures consistent access control across an organization
• Rule-based authorization uses predefined rules to determine access rights based on user attributes, object properties, or contextual factors
  • Rules can be expressed as if-then statements or using a policy language
• Attribute-based authorization evaluates user attributes, object attributes, and environmental conditions to make access decisions
  • Attributes can include user roles, security clearance, time of day, or location
• Capability-based authorization associates permissions directly with objects rather than users
  • Users possess capabilities (tokens) that grant them specific access rights to objects
• Delegated authorization allows users to grant a portion of their permissions to other users or processes
  • Useful for temporary access or when users need to share resources with collaborators

File System Security

• File system security controls access to files and directories and protects against unauthorized modification or disclosure
• File permissions determine the actions users can perform on files and directories (read, write, execute)
  • Permissions can be assigned to individual users, groups, or roles
• Access control lists (ACLs) provide granular control over file access by specifying permissions for each user or group
  • ACLs can be used to grant or deny access to specific files or directories
• File encryption protects the confidentiality of sensitive data by encoding it with a secret key
  • Encrypted files are unreadable without the corresponding decryption key
• Secure deletion techniques ensure that deleted files cannot be recovered by unauthorized parties
  • Methods include overwriting file data, using secure deletion tools, or encrypting files before deletion
• File integrity monitoring detects unauthorized changes to files by comparing their current state to a known baseline
  • Helps identify malicious modifications, accidental changes, or file corruption
• Auditing and logging track file access and modification activities for security analysis and incident response
  • Log entries include details such as user identity, timestamp, and the action performed (read, write, delete)
• Regular backups protect against data loss due to hardware failure, file corruption, or ransomware attacks
  • Backups should be stored securely and tested regularly to ensure their reliability

Privilege Management

• Privilege management involves controlling and monitoring the privileges assigned to users and processes
• Principle of least privilege (PoLP) ensures that users and processes have only the minimum privileges necessary to perform their tasks
  • Reduces the potential impact of security breaches and limits the scope of unauthorized actions
• Privilege separation divides a system or application into components with different levels of privilege
  • Critical components run with higher privileges and are isolated from less trusted components
• Privilege escalation occurs when a user or process gains higher privileges than initially assigned
  • Can be legitimate (sudo command) or malicious (exploiting vulnerabilities to gain unauthorized privileges)
• Privilege bracketing grants elevated privileges to a process for a limited time or scope
  • Privileges are dropped when no longer needed, reducing the window of vulnerability
• Privilege auditing monitors and logs the use of privileged accounts and actions
  • Helps detect misuse, abuse, or unauthorized privilege escalation attempts
• Regular privilege review ensures that user privileges align with their current roles and responsibilities
  • Unused or excessive privileges should be revoked to maintain the principle of least privilege

Security Policies and Best Practices

• Security policies establish the rules, guidelines, and procedures for maintaining the security of an operating system
• Access control policies define who can access system resources, under what conditions, and with what permissions
  • Policies should be based on the principle of least privilege and enforce strong authentication and authorization mechanisms
• Password policies specify requirements for password strength, complexity, expiration, and storage
  • Policies may include minimum length, mandatory use of special characters, and regular password changes
• Data classification policies categorize data based on its sensitivity and define appropriate handling and protection measures
  • Classifications can include public, internal, confidential, or restricted data
• Incident response policies outline the procedures for detecting, reporting, and responding to security incidents
  • Policies define roles and responsibilities, communication channels, and escalation procedures
• Network security policies govern the secure configuration and use of network resources and services
  • Policies may cover firewall rules, VPN access, wireless security, and remote access protocols
• Backup and disaster recovery policies ensure the regular backup of critical data and define procedures for recovering from disasters or system failures
  • Policies specify backup frequency, storage locations, retention periods, and testing requirements
• Security awareness and training programs educate users about security best practices, policies, and their responsibilities
  • Regular training helps users identify and report potential security threats and maintain a strong security culture