Question

A challenge response scheme can be used to authenticate a client to a

server on a network.

a) What is the main feature of a challenge response scheme compared to just sending

the password?

b) Why should a nonce be used in challenge response authentication?

c) The challenge response protocol in WEP shared key authentication was/is insecure.

Explain the weakness.

Answer 1

a) Challenge response scheme basically a Authentication Protocol which identify the legitimate user who is requesting to access the services or machines based on the challenge- response scheme.

for example:in password based challenge-response scheme , user generate challenge at client side

CH1 = Hash(challenge)+key1 ,challenge is random number generated by server , key1 = user password

CH1 ----> Server, now server generate the CH2 = Hash(same challenge)+key2, key2 = copied of user password at server side

if CH1 = CH2 ------> client is authenticated else invalid user

this protocol is provide defend against man in the middle attack.

b) To make every challenge- response pair sequence distinguish from other ,nonce is added in challenge - response authentication based system.

c) This protocol uses the shared key to encrypt the challenges ,here password is used as a key that can be alter if it is not strong then it becomes easy to break the keys for attackers.