The correct answer is Message digest.To preserve the integrity of a message, the message is passed through an algorithm called a cryptographic hash function.The function creates a compressed image of the message, called a digest.To check the integrity of a message, the receiver runs the cryptographic hash function again and compares the new digest with the previous one.If both are the same, the receiver is sure that the original message has not been changed.To ensure message integrity and message origin authentication, Message Authentication Code (MAC) is created using a combination of hash function and secret key.A sender sends the message and the MAC to a receiver over the insecure channel.The receiver separates the message from the MAC.He then makes a new MAC from the message and the secret key.Bob then compares the newly created MAC with the one received.If the two MACs match, the message is authentic and has not been modi?ed by an adversary.