# Symmetric Ciphers Questions and Answers – The Data Encryption Standard (DES) and It’s Strength – I

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This set of Cryptography Multiple Choice Questions & Answers (MCQs) focuses on “The Data Encryption Standard (DES) and It’s Strength”.

1. DES follows
a) Hash Algorithm
b) Caesars Cipher
c) Feistel Cipher Structure
d) SP Networks

Explanation: DES follows Feistel Cipher Structure.

2. The DES Algorithm Cipher System consists of ____________rounds (iterations) each with a round key
a) 12
b) 18
c) 9
d) 16

Explanation: The DES Algorithm Cipher System consists of 16 rounds (iterations) each with a round key.

3. The DES algorithm has a key length of
a) 128 Bits
b) 32 Bits
c) 64 Bits
d) 16 Bits

Explanation: DES encrypts blocks of 64 bits using a 64 bit key.

4. In the DES algorithm, although the key size is 64 bits only 48bits are used for the encryption procedure, the rest are parity bits.
a) True
b) False

Explanation: 56 bits are used, the rest 8 bits are parity bits.

5. In the DES algorithm the round key is __________ bit and the Round Input is ____________bits.
a) 48, 32
b) 64,32
c) 56, 24
d) 32, 32

Explanation: The round key is 48 bits. The input is 32 bits.

6. In the DES algorithm the Round Input is 32 bits, which is expanded to 48 bits via ____________
a) Scaling of the existing bits
b) Duplication of the existing bits

Explanation: The round key is 48 bits. The input is 32 bits. This input is first expanded to 48 bits (permutation plus an expansion), that involves duplication of 16 of the bits.

7. The Initial Permutation table/matrix is of size
a) 16×8
b) 12×8
c) 8×8
d) 4×8

Explanation: There are 64 bits to permute and this requires a 8×8 matrix.

8. The number of unique substitution boxes in DES after the 48 bit XOR operation are
a) 8
b) 4
c) 6
d) 12

Explanation: The substitution consists of a set of 8 S-boxes, each of which accepts 6 bits as input and produces 4 bits as output.

9. In the DES algorithm the 64 bit key input is shortened to 56 bits by ignoring every 4th bit.
a) True
b) False

Explanation: Every 8th bit is ignored to shorten the key length.