Q.1 Suppose Alice, Bob, and Carol want to use secret key technology to authentic
ID: 3910041 • Letter: Q
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Q.1 Suppose Alice, Bob, and Carol want to use secret key technology to authenticate each other. If they all used the same secret key K, the Bob could impersonate Carol to Alice (actually any of the three can impersonate the other to the third). Suppose instead that each had their own secret key, so Alice uses Ka, Bob uses KB and Carol Uses Kc. This means that each one to prove his or her identity responds to a challenge with a function of his or her secret key and the challenge. Is this more secure than having them all use the same secret key K? Q.2 Below an authentication protocol, based on shared secret key, is called Two-way authentication using a challenge-response protocol. If you are intruder, say your name is Trudy, how can you break this protocol. Explain it'? 1 2 Re 3 KAB (RB) 4 KAB (RA) A: ID of A. Ra, RB: Random numbers generated by A and B. KAB: shared secret key between A and B. KAB (RA), KAB (RB): Encryption of Ra and RBExplanation / Answer
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If Alice, Bob and Carol all have the same secret key K to authenticate themselves, then the problem is that they could impersonate each other. For example, with the same public key Bob could impersonate as Alice to Carol. And like this might occur. Thus here the security is very less. But when we have got the private keys and Alice uses Ka, Bob uses Kb and Carol uses Kc such that each use their own secret key, then each one to prove their identify responds with a function of his/her secret key and the challenge. So this is somewhat like a digital signature in which each have got the private keys which can authenticate each individual. This is obviously more secure as impersonation cannot occur and also there is a greater security and also the use of digital signature in using the secret key for individual authentication. Thus this individual usage of keys is obviously more secure than all of them using the same key K.
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