Protection and Security

A fence register is used to relocate data to protect the memory.

Trojan horses disguise themselves as legitimate or useful software to trick users into installing them. Once executed, they provide unauthorized access or perform malicious actions. Unlike viruses, they don't self-replicate but rely on social engineering.

An access matrix is a security model that defines what subjects (users, processes) can perform what operations on objects (files, resources). Rows represent subjects, columns represent objects, and each cell contains access rights. This model forms the basis for implementing access control policies.

Computer viruses are malicious programs that replicate by inserting copies into other programs or documents. They can cause damage by modifying or destroying files, crashing systems, and disrupting normal operations. Unlike worms, viruses typically require user action to spread.

In cryptography, both public and private keys are used for encryption and decryption. Public key encryption uses a key pair - one public (shared) for encryption and one private (secret) for decryption, or vice versa for digital signatures. Symmetric encryption uses a single shared key, while asymmetric uses the public/private pair.

Trojan horse programs are often designed to steal sensitive information like passwords by appearing legitimate. They can capture keystrokes, read password files, or trick users into entering credentials. The stolen passwords are then transmitted to attackers for unauthorized access.

Mandatory Access Control (MAC) is a security model where access rights are regulated by a central authority based on multiple levels of security. Users cannot change access permissions, which are system-defined. This contrasts with Discretionary Access Control (DAC) where resource owners control access.

Passwords are the most common authentication mechanism to verify user identity. Users provide secret passwords that only they should know, proving their identity to the system. Proper password policies and hashing are essential for maintaining security against unauthorized access.

Computer worms are standalone malicious programs that replicate themselves to spread to other computers across networks. Unlike viruses, they don't need to attach to host programs - they can run independently and exploit vulnerabilities to propagate. Worms can consume bandwidth and disrupt system operations.

Cryptanalysis is the science of analyzing information systems to discover hidden aspects of ciphers. It involves finding weaknesses in encryption algorithms to recover plaintext without knowing the key. This field drives advances in cryptography by exposing vulnerabilities.

Trap doors (or backdoors) are secretly inserted code or hardware features that bypass normal authentication. Developers or attackers might leave these intentional vulnerabilities to gain unauthorized access later. They represent serious security risks as they can be exploited by anyone who discovers them.

Discretionary Access Control (DAC) is a security model where resource owners determine who can access their resources. Users can set permissions on files and other objects they own, granting access to other users at their discretion. This contrasts with Mandatory Access Control where the system enforces policies.