Cryptography 2076

Attempt all questions.

1. Answer following questions in short (any five)

        a. How MAC differs from Hash? Is authentication and authorization refers to same term or different? Justify.

        b. Differentiate between virus and worms.

        c. What is the importance of Trap Door function in cryptography?

        d. How many rounds are used in AES and what does the number of rounds depend on?

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

        f. List the five services that PGP operation is based on.

        g. John obtains Peter's credit card number and performs shopping. Does it violate confidentiality or integrity or both? Justify.

2. a. What is Fermat's Little theorem? What is the totient of a prime number? Give an example.

                OR

    Define primitive root of a prime number with a suitable example,

    b. Find the multiplicative inverse of 11 in Z₂₆ using extended Euclidean algorithm.

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

        i) 27 mod 5        ii) 36 mod 12        iii) -18 mod 14        iv) -7 mod 10        v) -13 mod 7

    b. How can RSA can be used for generating public and private key? Explain.

4. a. Encrypt the message "computing for human life" to playfair cipher using key "BSCCSIT".

    b. Explain about the working mechanism of Kerberos.

5. a. Does it possible to design collision free hash function? What does birthday attack refers to? Explain.

            OR

    What is the role of SSL Record Protocol in SSL/TLS? Explain.

    b. Describe the "mix columns" transformation that constitutes the third step in each round of AES.

6. a. Define digital signature. How certificates are issued in PKI trust models? Explain.

    b. List the modes of operation in cryptography? Describe the Fiestel cipher structure.