1. 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
c) Addition of zeros
d) Addition of ones
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.
2. 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.
3. 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.
4. 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.
5. What is the size of the key in the SDES algorithm?
a) 24 bits
b) 16 bits
c) 20 bits
d) 10 bits
Explanation: The size of the key in the SDES algorithm is 10 bits.
6. Assume input 10-bit key, K: 1010000010 for the SDES algorithm. What is K1?
a) 10100100
b) 01011011
c) 01101000
d) 10100111
Explanation: The permuted key P10 = 1000001100. Input to P8: 0000111000 and
K1 is 10100100.
7. Assume input 10-bit key, K: 1010000010 for the SDES algorithm. What is K2?
a) 10100111
b) 01000011
c) 00100100
d) 01011010
Explanation: Input to P8: 0010000011 and K2 is 01000011.
8. The Ciphertext for the Plaintext 01110010, given that the keys K1 is 10100100 and K2 is 01000011 is
a) 01110111
b) 10010110
c) 01010110
d) 01000101
Explanation: Perform the SDES algorithm and compute the cipher text.
9. The Ciphertext for the Plaintext 11010101, given that the key is 0111010001 is
a) 00010001
b) 10110010
c) 11010010
d) 01110011
Explanation: Perform the SDES Encryption algorithm and compute the cipher text.
10. The Plaintext for the Ciphertext 00100010, given that the key is 1111111111 is
a) 01100111
b) 00001010
c) 01001000
d) 01001100
Explanation: Perform the SDES Decryption algorithm and compute the cipher text.