Q: C-17 Alice and Bob shared an n-bit secret key some time ago. Now they are no
ID: 3668466 • Letter: Q
Question
Q: C-17 Alice and Bob shared an n-bit secret key some time ago. Now they are no longer sure they still have the same key. Thus, they use the following method to communicate with each other over an insecure channel to verify that the key KA held by Alice is the same as the KB held by Bob. Their goal is to prevent an attacker from learning the secret key.
Alice generates a random n-bit value R.
Alice computes X =KA O R where denotes the exclusive or Boolean function, and sends X to Bob.
Bob computes Y = KB O X and sends Y to Alice.
Alice compares X and Y. If X = Y, she concludes that KA = KB, that is, she and Bob have indeed the same secret key.
Show how an attacker eavesdropping the channel can gain possession of the shared secret key.
Explanation / Answer
This attack is similar to man in the middle attack.
Scenario explaination , how attacker eavesdrops the messages and key ...
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Alice, Bob main objective is to share their keys more securely.
So firstly alice asks bob to send public key. Then intruder (attacker) will eavesdrops the
bob key whle sending.
Then alice sends her public key to Bob. Then intruder will eavesdrops the alice key too..
In the mean while, both keys will be enctypted with intruder key.
So that intruder can decrypt all messgaes. Alice, Bob dont know about this intruder activity.
By diagrammatically to be shown as follows:
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Alice <------ intruder **public key ----- Bob
Alice ------- intruder **public key -----> Bob
Now intruder can decrypt the both alice and bob messages.
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