Symmetric key material may also be used to authenticate, as mentioned in Chapter 6, Cryptographic Fundamentals for IoT Security Engineering. Message Authentication Codes (MACs) are generated using a MAC algorithm (such as HMAC and CMAC) with a shared key and known data (signed by the key). On the receiving side, an entity can prove the sender possessed the pre-shared key when the computed MAC is shown to be identical to the received MAC. Unlike a password, symmetric keys do not require the key to be sent between the parties (except ahead of time or agreed on using a key establishment protocol) at the time of the authentication event. The keys will either need to be established using a public key algorithm, input out of band, or sent to the devices ahead of time, encrypted using a Key Encryption Key (KEK).