Message authentication is a mechanism or service used to verify the integrity of a message. It assures that data received by an entity are exactly the same as sent by the sending entity. It indicates that the received message contains no modification, insertion, deletion or replay of its original contents. It also ensures that the purported identity of the sender is valid. In symmetric encryption scheme authentication is provided among the communication entities through shared secret key. If a sender encrypts his message using his own private key it is also one form of authentication the following are the two most common cryptographic techniques employed to provide message authentication in a communication network.
