CAS-004 Security Architecture Practice Question
A security architect is designing a zero trust architecture for a financial institution. Which principle is fundamental to the zero trust model?
⚠ Common exam trap
CAS-005 often tests zero trust principles by offering variations of 'trust but verify' or 'VPN for all access.' The trap is confusing zero trust with traditional defense-in-depth, which still relies on perimeter trust.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Assume breach and verify explicitly
The fundamental principle of zero trust is 'assume breach and verify explicitly,' meaning no user or device is trusted by default, regardless of location. Every access request must be authenticated and authorized based on multiple factors, and least privilege is enforced. This principle is core to zero trust architecture as defined by NIST SP 800-207.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Trust but verify all network traffic
Why it's wrong here
Zero trust removes implicit trust based on network location; verifying traffic after granting network-level trust contradicts that. Trust-but-verify describes perimeter or defence-in-depth models, where internal network traffic is trusted by default, which zero trust explicitly rejects.
- ✗
Use VPNs for all remote access
Why it's wrong here
VPNs grant broad network access once the tunnel is established, contradicting zero trust's per-request verification and least-privilege access. They are tempting because they encrypt traffic and authenticate users at the perimeter, which suits legacy remote-access scenarios, but they create an implicit trust zone rather than enforcing continuous authorisation.
- ✗
Perimeter-based security is sufficient
Why it's wrong here
Zero trust assumes no implicit trust from network location, so perimeter-based security directly contradicts the model's verify-explicitly, least-privilege stance. Perimeter defence is tempting because it was the traditional castle-and-moat design, and it remains valid for legacy on-premises segmentation, but not for zero trust identity-centric access.
- ✓
Assume breach and verify explicitly
Why this is correct
Zero trust removes implicit trust based on network location. Assuming breach means every request is treated as potentially hostile, so each access is verified explicitly using identity, device and context signals before granting least-privilege access, which is fundamental to the model.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
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