OS Protection and Security

• OS protection and security involve safeguarding computer resources, extending to the operating system and data through ensuring integrity, confidentiality, and availability.
• The goals of protection are to prevent malicious misuse and ensure resources are used according to system policies set by designers/administrators, and to minimize damage from errant programs.
• Protection systems provide mechanisms for enforcing policies, with administrators and users responsible for effective implementation.

Principles of Protection

• The principle of least privilege states programs, users, and systems should be given just enough privileges to perform tasks, minimizing potential harm.
• Using SGID programs with group ownership instead of SUID with root ownership can limit damage if something goes wrong.
• The root account should be reserved for tasks needing root privileges, with system administrators using an ordinary account for daily activities.

Domain of Protection

• A computer can be viewed as a collection of processes and objects (hardware & software).
• The need to know principle dictates processes should only access objects required for their task, in necessary modes, and during the required timeframe.
• A protection domain specifies the resources a process can access.
• An access right is the ability to execute an operation on an object.
• A domain is a set of < object, { access right set } > pairs.
• The association between a process and a domain may be static or dynamic, necessitating ways to change domain contents or switch domains.
• Domains can be realized as users, processes, or procedures.

Access Matrix

• A the model of protection can be viewed as an access matrix, wherein columns represent system resources, and rows represent protection domains.
• Entries in the matrix indicate the type of access a domain has to a resource.
• Domain switching can be supported by providing "switch" access to other domains.

Copy rights

• The ability to copy rights is an asterisk (*) indicating that processes in a domain can copy access within the same column for the same object.
• Removing the asterisk means the right is transferred, rather than copied, and is called a transfer right.
• Copying the right but not the asterisk adds the access right to a new domain without propagating further, termed a limited copy right.
• The owner right allows adding or removing of existing rights.
• Control rights allow processes in one domain to affect rights in others.

Implementation of Access Matrix

• The global table approach involves a large table with < domain, object, rights > entries.
• The global table approach is difficult to implement due to its size and lack of grouping abilities.
• Access lists for objects can be implemented by keeping a list of access rights for each object and a default access rights list.
• Capability lists for domains involve keeping each row of the table as a capability list for that domain, protected via tags or segmented memory.
• A lock-key mechanism uses locks and keys (unique bit patterns) for resources and domains, respectively, granting access if a domain's key matches a resource's lock.
• Each method has pros and cons; many systems use a combination of these.

Operating System Security

• OS security ensures the integrity, confidentiality, and availability of the system.
• OS security involves protecting systems from viruses, worms, malware, and hacker intrusions, using preventive controls to safeguard system assets from theft, modification, or deletion.
• Security provides safety for computer resources by assuring the OS's integrity, confidentiality, and availability.

Threats and Attacks

• Security threats can be malicious or accidental.
• A threat is a program that has the potential to harm a system.
• An attack is a security breach that provides unauthorized access to resources.
• Malicious threats involve destructive code leading to vulnerabilities while accidental threats are typically easier to defend against.
• Violations to security can include breach of integrity (unauthorized data modification), theft of service (unauthorized resource use), breach of confidentiality (unauthorized data reading), breach of availability (unauthorized data destruction), and denial of service (preventing legitimate system use).
• System security aims to ensure integrity (preventing unauthorized access and modification), secrecy (limiting access to authorized users), and availability (ensuring all authorized users can access system resources).

Types of Security Threats

• Program threats occur when a user program leads to malicious actions, examples include viruses, Trojan Horses, Logic Bombs, and Trap Doors
• Viruses replicate, modify/delete files, and can crash systems.
• Trojan Horses steal user credentials.
• Logic Bombs cause software to misbehave when specific criteria are met.
• Trap Doors are security weaknesses allowing illegal actions without user knowledge.
• System threats misuse system services and network connections, which can trigger program threats, some examples are Port Scanning, Worms, and Denial of Service.
• Port Scanning identifies system vulnerabilities.
• Worms exhaust system resources to choke performance.
• Denial of Service prevents legitimate system use.
• Threats to operating systems include malware (viruses, worms, Trojan Horses) that corrupt files, replicate, and can crash a system, and network intrusion (masqueraders, misfeasors, unauthorized users).
• Buffer overflow is a common issue where more input than allotted overwrites a buffer, which can crash a system or allow inserted malware to take control.

OS Security Measures

• Authentication verifies users and authenticates programs they execute, generally through username/password, biometric user attribution, or user card/key.
• One-time passwords add further security and can be implemented through secret keys, random numbers, or network passwords.
• Firewalls monitor all network traffic for local security.
• Firewalls is an efficient way of protecting network systems or local systems from any network-based security threat.
• Physical security is vital because physical access can allow attackers to edit, remove, or steal important files.