The classic "castle and moat" model: dangerous outside, safe inside. This model fails in the cloud and remote-work era — it doesn't protect against insider threats or lateral movement attacks. Zero Trust: "Never trust, always verify" — every request, every user, every device is verified regardless of location or network.
Zero Trust principles: 1) Identity verification (authentication on every access), 2) Least privilege access (only necessary permissions), 3) Micro-segmentation (dividing the network into small segments), 4) Continuous monitoring (ongoing observation and anomaly detection). BeyondCorp (Google) was the first company to widely implement Zero Trust. NIST SP 800-207 is the official Zero Trust standard document.
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