Cryptography 2075

Question Paper Details
Tribhuwan University
Institute of Science and Technology
2075
Bachelor Level / Fifth Semester / Science
Computer Science and Information Technology ( CSC316 )
( Cryptography )
Full Marks: 60
Pass Marks: 24
Time: 3 hours
Candidates are required to give their answers in their own words as far as practicable.
The figures in the margin indicate full marks.

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1. Answer following questions in short (any five)

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

2 marks
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        b. Differentiate between virus and Trojan horse.

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

2 marks
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        d. Differentiate between transposition cipher and substitution cipher?

2 marks
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        e. What does Zn refer to in cryptography? Illustrate with an example.

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

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

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

5 marks
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                            OR

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

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

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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

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

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

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

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5. a) Explain about PGP.                                                                                                 OR

      What is the role of the SSL Record Protocol in SSL/TLS? Explain.                             
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    b) Describe the method for generating Round Constant table in AES algorithm in Add Round Key phase. Assume the number of rounds is 10.                                                   

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

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

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