# Message Authentication Code (MAC)

The MAC field is similar to the checksum fields used in other PDUs. However, where checksum are used for error detection (corruption during transport), MAC is used as a security layer which check if the message has been altered/tempered with during transit.

The way it works can be summarized in three steps:

1. Sender create a digest1 of the data payload
2. Sender encrypt the data payload using the symmetric key, encapsulate it and pass the result to the Transport Layer
3. Receiver decrypt the data payload using the symmetric key and create a digest of the payload using the same algorithm and hash value that the sender. If the two digests match, the integrity of the message is confirmed
1. A digest is basically a small amount of data derived from the actual

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