Security Architecture and Engineering
Core concepts
This domain covers secure design principles and cryptography. Know least privilege, separation of duties, defense in depth, fail-safe/fail-secure, simplicity, and zero trust. Understand security models: Bell-LaPadula (confidentiality: no read up, no write down), Biba (integrity: no read down, no write up), Clark-Wilson (integrity via well-formed transactions), and Brewer-Nash (dynamic separation of duty). Know TCB, reference monitor, and the security kernel.
Cryptography
Distinguish symmetric (AES, fast, key distribution problem) from asymmetric (RSA/ECC, slow, solves key exchange and provides non-repudiation via digital signatures). Know hashing provides integrity (not confidentiality) and that salting defeats rainbow tables. Understand digital signatures = hash + private key; verification uses the public key. Know PKI, certificate authorities, and the difference between encryption (confidentiality) and signing (integrity/authenticity).
Traps
A frequent trap is assigning non-repudiation to symmetric crypto - it requires asymmetric keys. Another is confusing Bell-LaPadula and Biba directionality. Watch for questions that treat hashing as encryption. Also, fail-open vs fail-secure: fail-secure protects data but may block availability; the "right" answer depends on the stated priority.
Rule of thumb
Ask what property is needed: confidentiality → encryption, integrity → hash/MAC, authenticity/non-repudiation → digital signature. Match the model to the property (Bell-LaPadula = confidentiality, Biba = integrity).