1.2. Defense in Depth: Layers of Security

💡 First Principle: No single security control is perfect. Every lock can be picked, every wall can be scaled, every firewall can be bypassed. Security works by layering multiple controls so that when one fails — and it will — others catch the attack before damage is done.

Think of a medieval castle. It doesn't rely on just one wall. There's a moat, an outer wall, an inner wall, guard towers, a drawbridge, and armed defenders. Each layer makes it harder for an attacker to succeed, and each serves a different purpose. The moat deters casual attackers. The outer wall stops those who try harder. The towers let defenders detect intruders. The armed guards respond to breaches.

What breaks without defense in depth? Everything. A company that relies solely on a perimeter firewall is one misconfigured rule away from a breach. An organization that trusts only antivirus software will miss zero-day malware, fileless attacks, and insider threats. Single-point-of-failure security is the most common mistake organizations make — and one of the most heavily tested concepts on this exam.