1. What is Trusted Third Party (TTP)? What are the problems with TTP? (3 points)

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2. Using Caesar cipher algorithm and key value = 4, encrypt the plain text “Network Security”. Show your work. (3 points)

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3. Using the following Polybius Square encrypt the plaintext “CRYPTOGRAPHY”. Show your work. (3 points)

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4. Let k be the encipherment key for a Caesar cipher. The decipherment key differs; it is 26 – One of the characteristics of a public key system is that the encipherment and decipherment keys are different. Why then is the Caesar cipher a classical cryptosystem, not a public key cryptosystem? Be specific.             (3 points)

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5. A cryptographer once claimed that security mechanisms other than cryptography were unnecessary because cryptography could provide any desired level of confidentiality and integrity. Ignoring availability, either justify or refute the cryptographer’s claim. (3 points)

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6. How can you ensure Authentication using Challenge and Response method? Explain and give an example. (4 points)

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