Security, privacy and data integrity
Security, privacy and data integrity tests how data is protected in storage and transmission: threat types, encryption, authentication, integrity checks and the privacy principles that limit what organisations may do with personal data.
Threats
A virus attaches to a host file; a worm replicates across networks without a host; a Trojan disguises itself as legitimate software; ransomware encrypts data and demands payment; spyware and keyloggers capture activity. Phishing uses fraudulent messages, pharming redirects through manipulated DNS, and DoS or DDoS attacks exhaust resources. Brute-force and dictionary attacks target passwords; man-in-the-middle attacks intercept traffic.
Encryption
Symmetric encryption uses one shared key: fast, but key distribution is the weakness. Asymmetric encryption uses a public/private key pair: the public key encrypts, the private key decrypts, which solves distribution but is slow. A digital signature is a hash of the message encrypted with the sender's private key; the recipient verifies it with the sender's public key, giving integrity, authenticity and non-repudiation. TLS uses asymmetric methods to agree a symmetric session key, then encrypts the session symmetrically.
Integrity and privacy
Checksums and hashes detect accidental corruption; parity detects only an odd number of bit errors and cannot correct them. Backups (full, incremental, differential) and RAID mirroring protect availability. Access rights, two-factor authentication and encryption at rest protect confidentiality. Data protection principles require lawful and fair processing, purpose limitation, data minimisation, accuracy, limited retention and security.
Worked example
Alice sends Bob a confidential, authenticated message. She generates a random session key K, encrypts the message with K, encrypts K with Bob's public key, hashes the message and encrypts the hash with her private key. Bob decrypts K with his private key, decrypts the message, recomputes the hash and compares it with the decrypted signature. Confidentiality comes from Bob's key pair; authenticity from Alice's.
Traps
Claiming encryption with the recipient's public key proves who sent it; saying a digital signature hides the message; thinking a firewall stops insider misuse or phishing; treating parity as error correction.