Authentication functions:

Message Authentication :

• A mechanism of source used to notify the integrity of message

• Assures the data received are exactly as sent (i.e. contain no modification, insertion ,deletion or replay)

• Assures that identity of the sender is valid

• When a hash function is used to provide message authentication, the hash function value is often referred to as a message digest.

Authentication function is of two levels of functionality :

• Lower Value produces an authenticator value used to authenticate a message.

• Higher Value : indicates a receiver to verify the authenticity of message.

Grouped into three classes

• Message Encryption : The ciphertext of the entire message serves as authenticator

• Message Authentication Code (MAC) : The function of the message, a secret key that produces a fixed-length value that serves as that authenticator.

• Hash Function: A function that maps a message of any length into fixed-length hash value which serves as the authenticator