Message Authentication- What is Message Authentication?

• Message authentication ensures that the message has been sent by a genuine identity and not by an imposter.

• The service used to provide message authentication is a Message Authentication Code (MAC).

• A MAC uses a keyed hash function that includes the symmetric key between the sender and receiver when creating the digest.

• Figure shows how a sender A uses a keyed hash function to authenticate his message and how the receiver B can verify the authenticity of the message.

• This system makes use of a symmetric key shared by A and B.

• A, using this symmetric key and a keyed hash function, generates a MAC.

• A then sends this MAC along with the original message to B.

• B receives the message and the MAC and separates the message from the MAC.

• B then applies the same keyed hash function to the message using the same symmetric key to get a fresh MAC.

• B then compares the MAC sent by A with the newly generated MAC.

• If the two MACs are identical, it shows that the message has not been modified and the sender of the message is definitely A.