Security Architecture and Engineering
What to know
Architecture questions reward understanding of design principles and where controls sit. Master defense in depth, least privilege, separation of duties, fail-safe versus fail-open, secure defaults, and trust boundaries. Know the classic models: Bell-LaPadula (confidentiality, no read up, no write down), Biba (integrity, no read down, no write up), Clark-Wilson (well-formed transactions), and how they map to real requirements. Understand reference monitor and TCB concepts at a conceptual level.
Know the shared-responsibility model for cloud service types (IaaS, PaaS, SaaS) and how the boundary shifts. Understand segmentation, microsegmentation, zero trust (verify explicitly, least privilege, assume breach), and where encryption fits: at rest, in transit, and key management with envelope encryption and HSM/KMS. Be able to reason about cryptography selection: symmetric for bulk, asymmetric for key exchange and signatures, hashing for integrity, and why algorithms like AES-GCM are preferred over ECB. Know secure SDLC and threat modeling placement early in design.
Traps
- Assuming the cloud provider secures customer data and identities under IaaS.
- Mixing Bell-LaPadula and Biba directions under time pressure.
- Treating zero trust as a product rather than an architecture principle.
- Choosing encryption without addressing key management, which is where failures occur.
Worked example / rule of thumb
A team wants to store card data in a database. Correct design: encrypt at rest with envelope encryption via KMS, restrict keys by role, tokenize where possible, log key use, and segment the database. Rule of thumb: encryption is only as strong as its key custody.