Problem 1 (Authentication) : Consider the following authentication protocol, which uses a classical cryptosystem. Alice generates a random message r, enciphers it with the key k she shares with Bob, and sends the enciphered message {r}k to Bob. Bob deciphers it, adds 1 to r, and sends {r + 1}k back to Alice. Alice deciphers the message and compares it with r. If the difference is 1, she knows that her correspondent shares the same key k and is therefore Bob. If not, she assumes that her correspondent does not share the key k and so is not Bob. Does this protocol authenticate Bob to Alice? If so, Why? Otherwise, explain why not.

Question

Mikayla Watts

Computers & Technology

17 October, 08:14

Problem 1 (Authentication) : Consider the following authentication protocol, which uses a classical cryptosystem. Alice generates a random message r, enciphers it with the key k she shares with Bob, and sends the enciphered message {r}k to Bob. Bob deciphers it, adds 1 to r, and sends {r + 1}k back to Alice. Alice deciphers the message and compares it with r. If the difference is 1, she knows that her correspondent shares the same key k and is therefore Bob. If not, she assumes that her correspondent does not share the key k and so is not Bob. Does this protocol authenticate Bob to Alice? If so, Why? Otherwise, explain why not.

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Answers (1)

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Terrance Mcconnell · Answer 1

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Explanation:

Yes, going by the question above, the protocol validates Bob to Alice for the reason that the key is only shared between Bob and Alice as well as the number which is being sent randomly. Therefore the invader won't be able to predict and response to that number. Because of the authentication protocol, that makes use of a classical cryptosystem thereby resulting into the possibility of an argument such that key finding is attainable via invader.