This document discusses several key concepts in information system security: Authentication involves verifying the identity of a user or system, usually through passwords, ID cards, or biometrics. Authorization determines what resources a user can access after authentication. Privacy/confidentiality ensures sensitive personal data and messages are kept secret through encryption. Integrity keeps information from being altered without authorization. Availability ensures security services and data remain accessible. Non-repudiation prevents denied participation in online transactions. Auditing records network activity and communications for security monitoring through system logging.