Authentication of Message

Introduction: – In the earlier chapters, you have learned about the various types and sub types of encryption technique along with their names. There are more in cryptography and cryptographic techniques that deals with the integrity of data and their threats. There is another type of data threat which is lack in authentication of message. In this case of threat the user is not sure whether the message he/she received is from the originator (one who has
origin or created the message) or not. In this tutorial you will learn about the cryptographic technique of authenticating a message.

The Message Authentication: –
Message authentication is the technique of detecting whether the message sent to the user is from the correct source or from the originator or not and this can be done using some cryptographic techniques that utilise the need of secret key as done at the time of encryption.

Message Authentication Code: –
Machine Authentication Code, popularly known as MAC code does a form of cryptographic check-sum on information or message that nurtures a session key to check for both accidental and intentional changes or alteration of information or message.

MAC address needs 2 forms of inputs, these are:

  • The information or message
  • The secret key


The secret key is only known to the originator or creator of the message and its projected recipients. This cryptographic technique allows the recipient to verify the messages’ integrity and check for authentication by looking for the shared secret key sent from the sender’s end.

The MAC gets generated as an encrypted checksum on the underlying message sent by the sender, which ensures the authentication of the message. If the sender is unknown to the secret key, the generated hash value will be different, which will inform the recipient that the message was not from the actual sender. Here’s a block diagram of how the MAC authentication takes place –

authentication of message

Types of MACs: –
There are 4 different types of MACs. These are: –

  • Unconditionally secure
  • Stream cipher based MAC
  • Hashing function based MAC
  • Block Cipher based MAC


Limitations of MAC: –

i) Message authentication can be successfully carried out to only a specific set of users who possesses the shared key.
ii) Non repudiation can be the assurance that the originator of the message cannot deny the fact that messages have been sent previously.


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