HMAC
Hash-based Message Authentication Code
A keyed hash that verifies both integrity and authenticity of a message.
HMAC combines a cryptographic hash with a shared secret key to produce a tag that proves both integrity and authenticity, so a recipient knows the message was not altered and came from a party holding the key. Its construction resists length extension attacks that affect naive keyed hashing. It is widely used in TLS, IPsec, API request signing, and token validation. The exam contrast is a plain hash or checksum, which detects accidental change but provides no authentication because anyone can recompute it.
Hash plus a secret key: proves both the integrity and the authenticity of a message.
Looking HMAC up is step one. Getting tested on it is step two.
A free account opens all 4 Domain 1 objectives, 271 exam-style questions with a lesson and a lab on each, a placement check that skips what you already know, and a dated plan. No card.
Not affiliated with or endorsed by CompTIA.