03 - Security Architecture and Engineering (Domain 3, 13%)¶

Domain Overview¶

Domain 3 covers how security is built into systems: architecture principles, security models, hardware/software security primitives, cryptography, and physical security. It contains some of the most memorization-heavy material on the exam, especially around cryptographic algorithms and security models.

Secure Design Principles¶

These principles guide architecture decisions and frequently appear in scenario questions:

• Least privilege - Grant the minimum access needed
• Defense in depth - Multiple, layered controls
• Fail secure / fail safe - Default to denial on error (fail-safe favors safety; fail-secure favors security; not always synonymous)
• Separation of duties (SoD) - No single person can complete a sensitive transaction
• Two-person integrity - Two people required for critical action (e.g., nuclear launch, key ceremony)
• Need-to-know - Access only to information necessary for one's job
• Open design (Kerckhoffs) - Security through algorithm secrecy fails; security must rely on key secrecy
• Economy of mechanism - Simple, easy-to-verify designs
• Complete mediation - Every access checked
• Psychological acceptability - Users will work around painful controls
• Least common mechanism - Minimize shared mechanisms across users
• Trust but verify - Older model
• Zero trust - Never trust, always verify, assume breach
• Privacy by design - Privacy baked in, not bolted on
• Secure by default - Out-of-box configuration is secure; users must explicitly weaken
• Shared responsibility - Cloud and outsourced models

Security Models¶

Security models formalize policy. CISSP requires distinguishing several:

Bell-LaPadula (BLP)¶

• Confidentiality model
• Multi-level security (MLS)
• Simple Security Property (ss-property): No read up
• Star Property (*-property): No write down
• Strong Star Property: No read or write at different levels
• Use case: military classified data

Biba¶

• Integrity model
• Mirror image of BLP
• Simple Integrity Property: No read down
• Star Integrity Property: No write up
• Invocation Property: Subject cannot invoke higher integrity subjects
• Use case: integrity-critical data

Clark-Wilson¶

• Integrity model emphasizing well-formed transactions and separation of duties
• Subject -> Program -> Object (transformation procedures, TPs)
• Constrained data items (CDIs) and unconstrained data items (UDIs)
• Integrity verification procedures (IVPs)
• Use case: commercial integrity (banking, accounting)

Brewer-Nash (Chinese Wall)¶

• Conflict-of-interest model
• Dynamic access based on prior accesses
• Use case: consulting firms with competitive clients

Take-Grant¶

• Token-based rights propagation
• Operations: take, grant, create, revoke

Harrison-Ruzzo-Ullman (HRU)¶

• Access matrix model
• Proves general safety problem is undecidable

Graham-Denning¶

• 8 protection rules for create/delete subject/object, transfer rights, etc.

Lattice-Based Access Control¶

• Mathematical model where subjects/objects are at lattice nodes
• Foundation for MAC

Non-interference¶

• Higher-level activity does not affect lower-level observations
• Confidentiality property

Information Flow¶

• Direction-based controls preventing flow violations
• BLP and Biba can both be modeled as information flow

System Security Capabilities¶

Trusted Computing Base (TCB)¶

• All hardware, software, and firmware components critical to security policy enforcement
• Must be trusted; compromise of TCB compromises security
• Smaller TCB is easier to evaluate

Reference Monitor¶

• Abstract concept enforcing access control
• Must be: tamperproof, always invoked, small enough to verify
• Implemented as the security kernel

Security Kernel¶

• Hardware, firmware, software implementing the reference monitor

Trusted Computing¶

• TPM (Trusted Platform Module) - hardware root of trust, secure key storage, attestation
• Secure boot - chain of trust from firmware to OS
• HSM (Hardware Security Module) - tamper-resistant cryptographic processing
• Secure enclaves: Intel SGX, AMD SEV, ARM TrustZone, Apple Secure Enclave

Common Criteria (ISO/IEC 15408)¶

• Evaluation Assurance Levels (EAL1 to EAL7)
• Protection Profiles (PP) - implementation-independent requirements
• Security Targets (ST) - specific product claims
• Targets of Evaluation (TOE) - product being evaluated
• Higher EAL = more rigorous evaluation, NOT necessarily more secure

TCSEC (Orange Book) - historical context¶

• Replaced by Common Criteria
• Levels A1, B3, B2, B1, C2, C1, D

System Architecture Vulnerabilities¶

Client-server¶

• Trust boundary at network
• Threats: MITM, replay, server compromise

Distributed systems¶

• Microservices: more attack surface, complex auth
• API gateways, service mesh (mTLS, identity)

IoT¶

• Resource-constrained: limited crypto, often no patching
• Long lifespans, often deployed in physically accessible locations
• Default credentials, weak update mechanisms
• Standards: NIST IR 8259, ISO/IEC 27400

Industrial Control Systems (ICS) and SCADA¶

• Purdue model: levels 0 to 5 from physical process to enterprise
• Long lifecycle (decades), patching difficult
• Safety > security trade-offs
• Standards: IEC 62443

Cloud¶

• Shared responsibility model varies by service model:
• IaaS: customer responsible OS up
• PaaS: customer responsible apps and data
• SaaS: customer responsible identity and data classification
• Multi-tenancy, side-channel risks
• Vendor lock-in
• Compliance (data residency, sovereignty)

Containers¶

• Shared kernel; escape risk
• Image scanning and signing required
• Runtime threat detection
• Pod security standards (Kubernetes)

Serverless¶

• No server to patch but execution context still requires security
• IAM permissions per function
• Cold start telemetry visibility limits
• Dependency vulnerabilities still apply

Embedded¶

• Firmware update mechanisms
• Secure boot, code signing
• Physical attacks (JTAG, glitching, side-channel)

Cryptography¶

Goals¶

• Confidentiality - Encryption
• Integrity - Hashes, MACs
• Authenticity - Digital signatures, MACs
• Non-repudiation - Digital signatures (asymmetric only)

Symmetric Ciphers¶

Block Cipher Modes¶

• ECB - Electronic Codebook; identical plaintext = identical ciphertext (BAD)
• CBC - Cipher Block Chaining; uses IV, sequential
• CFB / OFB - Stream-like with block cipher
• CTR - Counter mode; parallelizable
• GCM - Galois Counter Mode; AEAD (authenticated encryption); current standard
• CCM - Counter with CBC-MAC; AEAD

Asymmetric Algorithms¶

ECC provides equivalent security with smaller keys: ECC 256 ≈ RSA 3072.

Hash Functions¶

Password Hashing¶

• PBKDF2 - acceptable, configurable iterations
• bcrypt - widely used, work factor adjustable
• scrypt - memory-hard
• Argon2 - winner of Password Hashing Competition; modern recommendation

Always use a salt; never use a fast hash (SHA-256) directly for passwords.

MACs¶

• HMAC - keyed hash; authenticates and verifies integrity
• CMAC, GMAC - block-cipher-based MACs
• Poly1305 - paired with ChaCha20

Public Key Infrastructure (PKI)¶

Components: - Certificate Authority (CA) - issues certificates - Registration Authority (RA) - validates identity - Certificate Revocation List (CRL) - list of revoked certs - Online Certificate Status Protocol (OCSP) - real-time revocation check - OCSP Stapling - server attaches OCSP response, reduces client burden - Certificate - X.509 standard format - Subject - identity certificate is issued to - Issuer - CA that signed - Public key - subject's public key - Validity period - notBefore, notAfter - Extensions - SAN, key usage, EKU, basic constraints - CRL Distribution Points (CDP) - Authority Information Access (AIA) - OCSP responder URL

Certificate types: - Domain Validated (DV) - basic, automated - Organization Validated (OV) - org existence verified - Extended Validation (EV) - extensive verification, browser UI signal - Wildcard - covers all subdomains - SAN - covers multiple domains - Code signing - for executable signing

Cryptographic Attacks¶

• Brute force - Try all keys
• Dictionary - Try common passwords
• Rainbow table - Pre-computed hash lookups
• Birthday attack - Find collisions
• Known-plaintext - Attacker has plaintext-ciphertext pairs
• Chosen-plaintext - Attacker chooses plaintexts
• Chosen-ciphertext - Attacker chooses ciphertexts to decrypt
• Side-channel - Timing, power, electromagnetic, cache (Spectre, Meltdown)
• Replay - Reuse captured authenticator
• Meet-in-the-middle - Reduces effective key strength of double encryption
• Padding oracle - Exploits padding error responses (POODLE)
• Implementation flaws - Heartbleed, weak RNG

Quantum Threat¶

• Shor's algorithm threatens RSA, ECC (factoring/discrete log)
• Grover's algorithm halves symmetric key strength (AES-128 -> 64-bit equivalent)
• Post-quantum cryptography (PQC): NIST announced first standards 2024 (Kyber for KEM, Dilithium and Falcon for signatures, SPHINCS+)
• Crypto-agility important for migration

Key Management¶

• Generation: high-quality RNG, hardware-backed preferred
• Distribution: secure channels (KDC, PKI)
• Storage: HSM, KMS, secure enclave
• Rotation: scheduled or on compromise
• Escrow: third-party key holding for recovery
• Destruction: secure key erasure

Physical Security¶

CPTED (Crime Prevention Through Environmental Design)¶

• Natural surveillance (sight lines)
• Natural access control (fencing, landscaping)
• Territorial reinforcement (clear boundaries)
• Maintenance (broken windows theory)

Perimeter Controls¶

• Fencing classifications:
• 3-4 ft: deters casual intrusion
• 6-7 ft: deters most
• 8 ft + barbed wire: prevents determined intruders
• Bollards
• Lighting (continuous, standby, movable, emergency)
• CCTV

Access Controls¶

• Locks (key, combination, smart, biometric)
• Mantraps / sally ports / interlocking doors
• Turnstiles
• Badge readers (proximity, smart card)
• Biometric readers
• Visitor management systems

Inside the Facility¶

• Datacenter zone separation
• Server rack locks, cage locks
• Cable management (prevent tampering)
• Secure media storage
• Shredders, secure disposal containers

Environmental Controls¶

• HVAC (temperature 18-27 C, humidity 40-60%)
• Power: UPS for ride-through, generator for sustained
• Power conditioning, surge protection
• Fire detection: smoke, heat, flame
• Fire suppression:
• Wet pipe (most common, water always in pipes)
• Dry pipe (water released on activation)
• Pre-action (two-stage activation)
• Deluge (open sprinklers, large discharge)
• Gas (FM-200, Inergen, CO2 - safe for electronics)
• Older Halon banned by Montreal Protocol (ozone)
• Class A, B, C, D, K fire types

Personnel Safety in Physical Security¶

• Emergency exits unlocked from inside even when fail-secure on entry
• Evacuation routes
• Assembly points
• Buddy systems
• Active shooter / incident plans

Site and Facility Design¶

• Location: avoid flood plains, fault lines, high-crime areas
• Building construction: hardened walls, secure roof, blast resistance for high-risk
• Adjacent occupants matter (shared building risks)
• Concealment: avoid obvious signage for sensitive sites
• Layered zones (public lobby -> employee area -> sensitive zones)

Common Exam Pitfalls¶

• Confusing BLP (confidentiality) with Biba (integrity)
• Mixing up symmetric and asymmetric algorithm uses
• Picking ECB mode (always wrong for any modern use)
• Choosing fast hashes (SHA-256) for password storage
• Forgetting digital signatures require asymmetric crypto
• Confusing fail-safe (life) with fail-secure (data)
• Selecting wrong fire suppression for the asset type
• Forgetting non-repudiation requires asymmetric (MACs cannot provide)