Purpose of nonce in an end-point authentication protocol:
• A nonce is a number that is used by an end-point authentication protocol to identify whether the sender is live (the sender was currently on the network) or not.
• An end-point protocol never uses a nonce that is already used.
• Attacks due to connection replay can be protected by using a nonce.
• To authenticate Alice, Bob first chooses a nonce and sends it to Alice.
• Since Alice knows the Bob and Alice’s shared secret key, she encrypts the nonce and sends it again to Bob.
• Bob decrypts the received message using the same secret key and compares both the decrypted nonce and the original nonce.
• When both are same, then Bob knows that the Alice is currently on the network and ends the authentication process successfully.
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