Security Architecture and Engineering

What this domain actually tests

Security models, secure design principles, cryptography, and physical security — all at an architectural level. You are not implementing; you are choosing and justifying.

Cryptography is about which mechanism provides which property, not about maths:

Only a digital signature provides non-repudiation, because only the signer holds the private key and therefore cannot later deny having signed. A MAC provides integrity and authentication but not non-repudiation, because both parties share the key — either could have produced it. That distinction is a favourite.

Which key does what: encrypt with the recipient's public key (confidentiality); sign with your own private key (non-repudiation).

The traps

Key management matters more than algorithms. The exam rarely asks you to compare AES to 3DES. It asks how keys are generated, distributed, stored, rotated, escrowed, and destroyed — because that is where real systems fail, and it is a management concern.

The security models appear by name and are worth learning as one-liners:

• Bell-LaPadula — confidentiality. No read up, no write down. Military classification.
• Biba — integrity. No read down, no write up. (The mirror image.)
• Clark-Wilson — integrity through well-formed transactions and separation of duties.
• Brewer-Nash (Chinese Wall) — prevents conflicts of interest.

Bell-LaPadula is confidentiality, Biba is integrity. If you remember only one thing, remember that pair — and that they are opposites.

Secure design principles. Defence in depth, least privilege, separation of duties, fail-secure versus fail-safe (fail-secure protects the asset by defaulting to locked; fail-safe protects people by defaulting to open — and on the CISSP, human safety always wins, so a fire exit fails open).

Physical security is in scope and candidates forget it. Mantraps, bollards, lighting, CPTED, and fire suppression. Remember: for any question involving fire or physical danger, evacuate people first.

How to study it

Learn the four models as one-line cards. Then learn the property table above — and specifically, be able to say why a MAC does not give non-repudiation.

Then, for physical security, remember the single rule that overrides everything: life safety first. It resolves more questions here than any technical knowledge.