Security
Foundations
The CIA triad - confidentiality, integrity, availability - anchors nearly every question. Pair it with AAA: authentication (who you are), authorization (what you may do), accounting (what you did). Least privilege, separation of duties, and defense in depth limit the blast radius of a failure. Authentication factors are something you know, have, or are; MFA requires two different categories, so a password plus a PIN is not MFA. Zero trust assumes no implicit trust from network location.
Threats and controls
Malware families: viruses attach to files, worms self-propagate, trojans disguise themselves, ransomware encrypts and demands payment, spyware collects data. Social engineering targets people: phishing (email), spear phishing (targeted), vishing (voice), smishing (SMS), pretexting. A threat is who or what could cause harm; a vulnerability is a weakness; risk is likelihood times impact. Controls are preventive (firewalls, patching), detective (IDS, logs), or corrective (restore from backup).
Cryptography
Encryption protects confidentiality and is reversible with a key; hashing is one-way and verifies integrity; salting defeats rainbow tables. Symmetric encryption (AES) is fast but key distribution is hard; asymmetric (RSA, ECC) uses public/private key pairs for exchange and signatures. TLS protects data in transit; full-disk encryption protects data at rest.
Worked example
An email claims to be from IT and asks you to 'verify your password.' That is phishing. Report it, never enter credentials, and rely on MFA so a stolen password alone is not enough.
Traps
- Confusing authentication with authorization.
- Treating hashing as encryption - hashes are not reversible.
- Believing antivirus alone equals defense in depth.