# Symmetric message authentication code key

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## Definition Edit

In a **symmetric message authentication code (MAC) key,**

“ | [a] symmetric key is used to provide assurance for the integrity of data. There are three techniques used to provide this assurance: 1) use a symmetric encryption algorithm and a MAC mode of operation (e.g., CMAC using AES); 2) use a symmetric encryption algorithm and an authenticated encryption mode of operation (e.g., GCM or CCM using AES); and 3) use a hash-based MAC (HMAC). For data-in-transit, a symmetric MAC key has a short life, typically for a single message or for a single session (for example a TLS session). For stored data, the life of a symmetric MAC key tends to be for as long as the data needs to be protected. | ” |

## Overview Edit

"Note that when authenticated encryption mode is used, the same key is used for both the MAC and encryption/decryption, since both objectives are achieved by invoking a single mode of operation."