Information Security and Cryptography

Context: FIT1047_MOC · the security half of the unit (W10–12) — this note is the hub for the crypto cluster · frames what we protect and which tool provides it

Quick Revision

• 🎯 Objective: every bit is changeable, every host reachable worldwide, every device potentially hackable ➔ security = achieving specific goals (confidentiality, integrity, authenticity, non-repudiation) despite an active attacker.
• ⚡ Key Constraint: match the goal to the mechanism — encryption ⇒ confidentiality, hashes/MACs/signatures ⇒ integrity + authenticity. Using the wrong primitive (e.g. a plain hash for tamper-proofing) fails.

📝 Security goals

• Confidentiality ➔ keep data secret from eavesdroppers → provided by encryption (Symmetric Cryptography, Public Key Cryptography).
• Integrity ➔ detect any change to a message in transit → provided by MACs / hashes / signatures (Cryptographic Hash Functions).
• Authenticity ➔ know whom you are talking to → digital signatures + certificates (Authentication, Certificates and PKI).
• Non-repudiation ➔ a signer cannot deny having signed → only public-key signatures provide it (symmetric keys can’t — both sides hold the same key).

🧰 Three algorithm families

• Symmetric encryption ➔ one shared secret key; fast; the key-distribution problem → Symmetric Cryptography.
• Public-key (asymmetric) ➔ a key pair (public + private); solves distribution + enables signatures → Public Key Cryptography.
• Hash functions ➔ one-way fixed-length fingerprints; underpin integrity, signatures, password storage → Cryptographic Hash Functions.

🛡️ Countermeasures (beyond crypto)

• Mechanisms ➔ cryptography, firewalls, multi-factor authentication — plus knowing risks/threats, building secure systems, designing secure networks, and the human aspect.
• Roadmap ➔ W10 crypto + protocols; W11 network security (firewalls, access control, SSO/MFA); W12 threats, risk, attacks, malware.

⚠️ Common Mistakes

• 💡 Goal ≠ mechanism ➔ encryption alone gives confidentiality but not integrity — AES ciphertext can still be reordered/flipped; you need a MAC for tamper-detection.
• 💡 Non-repudiation is asymmetric-only ➔ a shared symmetric key can prove a message came from one of us, never which one — so it cannot bind a signer.

🧠 Active Recall

Why isn't "encrypt everything" a complete security solution?

Answer

• Short answer: encryption targets confidentiality only; it does not guarantee integrity, authenticity, or non-repudiation, so an attacker can still tamper with ciphertext or impersonate a party.
• Why: Goal decomposition ➔ each goal needs its own primitive — MAC/hash for integrity, signature + certificate for authenticity, public-key signature for non-repudiation — layered on top of the cipher.