What is defense-in-depth and how is it implemented across physical, cyber, and information domains?

What is defense-in-depth and how is it implemented across physical, cyber, and information domains?

• A. Defense-in-depth uses multiple overlapping layers of protection so no single failure yields a breach; implemented with physical barriers, access controls, surveillance; cyber controls (segmentation, firewalls, IDS/IPS), data encryption, monitoring; information security (policy, training, incident response)
• B. Defense-in-depth is single-layer protection
• C. Defense-in-depth only concerns the cyber domain
• D. Defense-in-depth advocates removing layers to speed decisions

Answer: (A)