Glossary · Security

MAC

Message Authentication Code

In plain language

A short code attached to a message that proves it came from the right sender and was not changed on the way.

The metaphor

Like a wax seal pressed with a stamp only the sender owns: if the seal is missing or cracked, the letter is not trusted.

Going deeper

How it works

The sender and receiver share a secret key.
The sender runs the message and the key through a formula and attaches the result.
The receiver repeats the calculation and compares; any change to the message breaks the match.
It works quietly inside HTTPS, Wi-Fi and software updates.

What can go wrong (example scenario)

A small firm's payment tool sent instructions to a bank. Someone altered the account number in transit, the code no longer matched, and the bank refused the altered copy.

In practice

A software update checks its code before installing.
A Wi-Fi connection rejects a frame that was altered in the air.
A bank API call includes a code so the bank can tell it came from the real app.

A question owners ask

Is this the same as a digital signature?

They are cousins. A message authentication code uses a shared secret, so both sides can create it. A digital signature uses a private key that only one side holds.

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