5.1. Basic Security Concepts

💡 First Principle: Security is a system of controls working together. No single firewall, password, or policy is sufficient. Defense in depth layers controls so that failure of any single control doesn't mean complete compromise. The goal is detection and response time—slow attackers enough that you catch them.

Think of security like layers of an onion: perimeter firewall, network segmentation, host firewalls, application security, data encryption. An attacker must peel through each layer, giving you opportunities to detect and respond.