1) 10 parties want to exchange messages securely using some symmetric key encryption technique like AES. The number of distinct key values required will be __

Solution: In symmetric encryption, every pair of communicating parties must have a separate key. For N parties, the number of keys will be NC2. For N = 10, 10C2 = 10  9 / 2 = 45.

2) 10 parties want to exchange messages securely using some public key encryption technique like
RSA. The number of distinct key values required will be __

Solution: In public-key or asymmetric encryption, every party is in possession of two keys, a public key and a private key. For N parties, the number of keys will be 2N. For N = 10, it will be 20.

3) What is the effective key length in triple-DES?

a. 56 bits
b. 112 bits
c. 168 bits
d. 192 bits

Solution: In triple-DES, we have three sequential runs of the DES algorithm. For the DES algorithm, the key size is 56 bits. Hence, in triple-DES, the effective key size will be 56 x 3 = 168 bits. Thus, the correct option is (c).

4) On what factor(s) does the security of the RSA algorithm depend on?

a. On the difficulty of breaking a large integer into its prime factors.
b. On the difficulty of solving the discrete logarithm problem.
c. Size of the key.
d. All of these.

Solution: The security of the RSA algorithm depends on the complexity of the prime factorization problem. Also, as the number of bits in the key increases, the constituent prime numbers also increase and hence the difficulty of factorization. The correct options are (a) and (c).

5) Which of the following is/are active attack(s)?

a. Interruption
b. Interception
c. Modification
d. Fabrication