Which measure do HMACs use?

• A. Symmetric key encryption
• B. Public key encryption
• C. Hashing
• D. All of the above

Answer: (C)

HMACs rely on a cryptographic hash function combined with a secret key to produce a tag that authenticates the message and ensures integrity. It uses hashing with a shared key, not encryption, to generate a MAC. That’s why the measure is hashing. Symmetric key encryption would aim at confidentiality, and public key encryption uses asymmetric keys for encryption or signatures, not the keyed-hash approach of HMAC. So the correct idea is hashing (with a secret key) to create a MAC.