What do the abbreviations MAC and MDC stand for, and what is each primarily used for?

Question

Accepted Answer

MAC = Message Authentication Code (keyed integrity). MDC = Manipulation Detection Code (keyless, used as a proxy in digital signatures).

MAC
MDC

Full name
Message Authentication Code
Manipulation Detection Code

Key required?
Yes (shared secret)
No

Primary use
Verify integrity + authenticate sender
Serve as a stand-in (proxy) for the document when signing

Also known as
Should be MIC (Message Integrity Code)
"Hash" in everyday usage, "Fingerprint" in PGP (MD5)

Key insight: An MDC alone does not guarantee integrity — because an attacker can modify the document and recompute the hash. You need to combine MDC with a digital signature to get integrity.
Go deeper:

Message authentication code (Wikipedia) — the keyed side of the family: how a shared secret turns a hash into a forgery-resistant tag.

	MAC	MDC
Full name	Message Authentication Code	Manipulation Detection Code
Key required?	Yes (shared secret)	No
Primary use	Verify integrity + authenticate sender	Serve as a stand-in (proxy) for the document when signing
Also known as	Should be MIC (Message Integrity Code)	"Hash" in everyday usage, "Fingerprint" in PGP (MD5)