Data Protection and Cryptography
Data Protection and Cryptography tests whether you can classify data, choose appropriate cryptographic controls, and manage keys across their lifecycle. GCT-2A-324 questions often ask what a control actually protects - confidentiality, integrity, authenticity, or non-repudiation - and where encryption stops being sufficient.
Core rules and concepts
- Classify data first; controls follow sensitivity, regulation, and retention requirements. DLP, masking, tokenization, and access control reduce exposure, but they are not interchangeable with encryption.
- Encryption at rest protects stored data; encryption in transit protects data on the wire. TLS provides channel confidentiality and integrity, not protection of data after it is decrypted at an endpoint.
- AES-GCM is authenticated encryption (AEAD), providing confidentiality and integrity. RSA-OAEP is for key transport; ECDHE provides forward secrecy in TLS. Hashes provide integrity, not confidentiality; HMAC adds a key for authenticity.
- Passwords need slow, salted, memory-hard hashing such as Argon2id, scrypt, or bcrypt - not SHA-256 alone. Salts defeat precomputation; they do not make a weak password strong.
- Key management covers generation, storage, rotation, separation of duties, and destruction. KMS envelope encryption protects data keys with a root key; HSMs protect high-value keys. PKI binds identities to certificates and requires revocation and renewal processes.
Worked example
A database stores customer PII. The team chooses AES-256-GCM with per-record data keys, wrapped by a KMS customer-managed key. The database, backups, and snapshots are encrypted; access is restricted by database roles; sensitive fields are masked in lower environments. Key rotation is annual for the root key and on demand after suspected compromise, and key use is logged. The reasoning: GCM detects tampering, envelope encryption limits blast radius, and masking reduces non-production exposure. Encrypting the disk alone would not stop an authorized application user from reading decrypted records.
Traps that cost marks
- Treating encryption as integrity protection unless the mode is authenticated.
- Storing encryption keys with the ciphertext or in application source code.
- Using a fast hash such as SHA-256 for password storage.
- Assuming TLS protects data at rest or that tokenization removes the need for access control.