250+ TOP MCQs on The Data Encryption Standard and It’s Strength

Cryptography Assessment Questions on “The Data Encryption Standard (DES) and It’s Strength”.

1. During decryption, we use the Inverse Initial Permutation (IP-1) before the IP.
a) True
b) False

Answer: a
Clarification: IP-1 is the first step and the last step is IP during decryption.

2. A preferable cryptographic algorithm should have a good avalanche effect.
a) True
b) False

Answer: a
Clarification: Thus statement is true as a change in one bit of the plaintext or one bit of the key should produce a change in many bits of the ciphertext. This is referred to as the avalanche effect.

3. The number of tests required to break the DES algorithm are
a) 2.8×10¹⁴
b) 4.2×10⁹
c) 1.84×10¹⁹
d) 7.2×10¹⁶

Answer: d
Clarification: There are 2⁵⁶ keys =7.2×10¹⁶.

4. The number of tests required to break the Double DES algorithm are
a) 2112
b) 2111
c) 2128
d) 2119

Answer: b
Clarification: For Double DES key is 2112 bits, should require 2111 tests to break.

5. How many keys does the Triple DES algorithm use?
a) 2
b) 3
c) 2 or 3
d) 3 or 4

Answer: c
Clarification: For Triple DES we can either have 2 or 3 keys.
Using two keys: c = Ek1(Dk2(Ek1(m)))
Using three keys: c = Ek3(Ek2(Ek1(m))).

6. In triple DES, the key size is ___ and meet in the middle attack takes ___ tests to break the key.
a) 2192 ,2112
b) 2184,2111
c) 2168,2111
d) 2168,2112

Answer: d
Clarification: The key size is 2168 and meet in the middle attack takes 2112 tests to break.

7. Using Differential Crypt-analysis, the minimum computations required to decipher the DES algorithm is
a) 2⁵⁶
b) 2⁴³
c) 2⁵⁵
d) 2⁴⁷

Answer: d
Clarification: Differential Crypt-analysis requires only 2⁴⁷ computations to decipher the DES algorithm.

8.Using Linear Crypt-analysis, the minimum computations required to decipher the DES algorithm is
a) 2⁴⁸
b) 2⁴³
c) 2⁵⁶
d) 2⁶⁴

Answer: b
Clarification: Linear Crypt-analysis requires only 2⁴³ computations to decipher the DES algorithm.