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ECF-GSF Core study materials
ECF-GSF Core study resources

ECF-GSF Core: Cryptography and Privacy

ECF-GSF Core · Work through your exam, one topic at a time.

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Cryptography and Privacy

What this domain tests

This domain tests algorithm and key-usage selection, PKI trust, TLS behaviour, and the privacy principles that decide whether a processing activity is lawful.

Core rules

  • Symmetric: AES is the standard; GCM gives authenticated encryption. Never reuse a nonce or IV with GCM. Avoid ECB because identical plaintext blocks produce identical ciphertext; prefer GCM or CBC with a separate HMAC.
  • Asymmetric: RSA or ECC for key exchange, signatures and small payloads - never for bulk data. Encrypt with the recipient's public key; sign with the sender's private key.
  • Hashing: SHA-256/384 for integrity; salted slow KDFs (bcrypt, Argon2, PBKDF2) for passwords; HMAC for keyed integrity. MD5 and SHA-1 are broken for collision resistance.
  • PKI: a CA signs a certificate binding identity to a public key; the chain terminates at a trusted root; revocation is published via CRL or OCSP; pinning reduces MITM risk.
  • TLS: TLS 1.3 mandates forward secrecy and removes legacy ciphers; enforce TLS 1.2 as the floor and disable downgrade paths.
  • Key management: generation, distribution, rotation, escrow or recovery, destruction. Compromise of the key defeats the algorithm.
  • Privacy: lawfulness, purpose limitation, data minimization, accuracy, storage limitation, integrity and confidentiality, accountability. A DPIA is required for high-risk processing; consent must be freely given, specific, informed and revocable.

Worked example

A vendor must send a confidential, signed price list. Signing: hash the document with SHA-256, sign the hash with the vendor's private key, and the buyer verifies with the vendor's public certificate. Confidentiality: encrypt the document, or its symmetric key, with the buyer's public key. Reasoning: the signature gives integrity, authenticity and non-repudiation; encryption gives confidentiality. Performing only one leaves the other property unmet, and reversing the keys gives no security at all.

Traps that cost marks

  • Claiming 'encrypt with the private key' provides confidentiality.
  • Storing passwords as a fast unsalted hash.
  • Believing the certificate itself encrypts data - it authenticates the endpoint while the cipher suite does the encryption.
  • Reusing a GCM nonce across messages with the same key, which destroys confidentiality and integrity.