In message authentication mode, a Message Authentication Code (MAC) results from an encryption function. The MAC is a cryptographic checksum that provides an integrity service. The most common method to generate a MAC using block ciphers is CBC-MAC, where a part of the last block of the chain is used as a MAC. For example, a MAC can be used to ensure that if a message is modified by an unauthorized entity. This can be achieved by encrypting the message with a key using the MAC function. The resultant message and MAC of the message once received by the receiver can be checked by encrypting the message received again by the key and comparing it with the MAC received from the sender. If they both match, then the message has not modified by unauthorized user thus integrity service is provided. If they both don't match, then it means that message is modified by unauthorized entity during the transmission.