Cryptography 2075

Attempt all questions.

1. Answer following questions in short (any five)

        a. The larger the size of key space, the more secures a cipher? Justify your answer.

        b. Differentiate between virus and Trojan horse.

        c. What is weak collision resistance property of hash function?

        d. Differentiate between transposition cipher and substitution cipher?

        e. What does Z_n refer to in cryptography? Illustrate with an example.

        f. What is the additive inverse of 2 in Z₁₀?

        g. John copies Mary’s homework. Does it violate confidentiality or integrity or both? Justify.

2. a) What do you mean by “Fiestel Structure for Block Ciphers”? Explain.                       

                            OR

How can a number can be tested for primality testing using Miller-Rabin algorithm? Explain.

    b) Divide 5x²+4x+6 by 2x+1 over GF(7).

3. a) Find the result of the following operations.            

    (i) 2 mod 5     (ii) 33 mod 3     (iii) -13 mod 10     (iv) -23 mod 10     (v) -8 mod 7

    b) How can Diffie-Hellman can be used for key exchange? Explain.                               

4. a) Encrypt the message “machine passed turing test” to playfair cipher using key “ALANTURING”.                                                                                                             

    b) What is the digital signature for, authentication of confidentiality? Justify your answer. What does security handshake pitfall refer to?                                                                  

5. a) Explain about PGP.                                                                                                 OR

    b) Describe the method for generating Round Constant table in AES algorithm in Add Round Key phase. Assume the number of rounds is 10.                                                   

6. a) Is hash and MAC resemble the same meaning? Explain how SHA generates 160 bit digest value?                                                                                                                      

    b) Define field. Differentiate between public key cryptography and private key cryptography.