The MAC algorithm takes two inputs, a secret key and an arbitrary-length message, to be authenticated. The output is a fixed length string of bits called a MAC or a tag. The MAC value protects the message's data integrity and its authenticity by allowing verifiers who possess the secret key to detect any changes to the message content. MAC algorithms can be constructed from other cryptographic primitives, such as cryptographic hash functions, like HMAC, or from block cipher algorithms such as CBC-MAC or CMAC. Microchip's SAM9G46 and SAM9M11 embed AES and SHA and are able to support several MAC algorithms such as HMAC, CMAC or CBC-MAC.