# Block ciphers and Data Encryption standard MCQs

1. In affine block cipher systems if f(m)=Am + t, what is f(m1+m2) ?.

A. f(m1) + f(m2) + t.

B. f(m1) + f(m2) + 2t.

C. f(m1) + t.

D. f(m1) + f(m2).

Answer= f(m1) + f(m2) + t

2. In affine block cipher systems if f(m)=Am + t, what is f(m1+m2+m3) ?.

A. f(m1) + f(m2) + f(m3) + t.

B. f(m1) + f(m2) + f(m3) +2t.

C. f(m1) + f(m2) + f(m3).

D. 2(f(m1) + f(m2) + f(m3)).

Answer= f(m1) + f(m2) + f(m3)

3. If the block size is 's', how many affine transformations are possible ?.

A. 2s (2s-1)(2s-1)(2s-12)………(2s-1(s-1)).

B. 2s (2s-1)(2s-2)(2s-22)………(2s-2(s-2)).

C. 2ss (2s-1)(2s-2)(2s-22)………(2s-2(s-1)).

D. 2s (2s-1)(2s-2)(2s-22)………(2s-2(s-3)).

4. What is the number of possible 3 x 3 affine cipher transformations ?.

A. 168.

B. 840.

C. 1024.

D. 1344.

5. Super-Encipherment using two affine transformations results in another affine transformation..

A. TRUE.

B. FALSE.

C. Nothing can be said.

D. None of the mentioned.

6. If the key is 110100001, the output of the SP network for the plaintext: 101110001 is.

A. 110100011.

B. 110101110.

C. 10110111.

D. 11111010.

7. Confusion hides the relationship between the ciphertext and the plaintext..

A. TRUE.

B. FALSE.

C. Nothing can be said.

D. None of the mentioned.

8. The S-Box is used to provide confusion, as it is dependent on the unknown key..

A. TRUE.

B. FALSE.

C. Nothing can be said.

D. None of the mentioned.

9. Which of the following slows the cryptographic algorithm –1) Increase in Number of rounds2) Decrease in Block size3) Decrease in Key Size4) Increase in Sub key Generation.

A. 1 and 3.

B. 2 and 3.

C. 3 and 4.

D. 2 and 4.

10. What is the size of the key in the SDES algorithm?.

A. 24 bits.

B. 16 bits.

C. 20 bits.

D. 10 bits.

11. Assume input 10-bit key, K: 1010000010 for the SDES algorithm. What is K1?.

A. 10100100.

B. 1011011.

C. 1101000.

D. 10100111.

12. Assume input 10-bit key, K: 1010000010 for the SDES algorithm. What is K2?.

A. 10100111.

B. 1000011.

C. 100100.

D. 1011010.

13. The Ciphertext for the Plaintext 01110010, given that the keys K1 is 10100100 and K2 is 01000011 is.

A. 1110111.

B. 10010110.

C. 1010110.

D. 1000101.

14. The Ciphertext for the Plaintext 11010101, given that the key is 0111010001 is.

A. 10001.

B. 10110010.

C. 11010010.

D. 1110011.

15. The Plaintext for the Ciphertext 00100010, given that the key is 1111111111 is.

A. 1100111.

B. 1010.

C. 1001000.

D. 1001100.

16. In SDES, Encryption algorithm can be  written as a composition of functions: IP-1 o fK2 o fK1 o SW o IP.

A. TRUE.

B. FALSE.

C. Nothing can be said.

D. None of the mentioned.

17. Assume input 10-bit key, K: 0010010111 for the SDES algorithm. What is K1?.

A. 101111.

B. 1011011.

C. 1101000.

D. 10100111.

18. The Plaintext for the Ciphertext 00001111, given that the key is 1111111111 is.

A. 1100111.

B. 1010.

C. 11111111.

D. 1101101.

19. The Plaintext for the Ciphertext 11110000, given that the key is 0000000000 is.

A. 1100111.

B. 0.

C. 1001000.

D. 1101100.

20. Assume input 10-bit key, K: 0010010111 for the SDES algorithm. What is K2?.

A. 11101010.

B. 11011011.

C. 1101000.

D. 10101111.

21. The Plaintext for the Ciphertext 10100101, given that the key is 0010010111 is.

A. 1100111.

B. 110110.

C. 1001000.

D. 1001100.

22. During decryption, we use the Inverse Initial Permutation (IP-1) before the IP..

A. TRUE.

B. FALSE.

C. Nothing can be said.

D. None of the mentioned.

23. A preferable cryptographic algorithm should have a good avalanche effect..

A. TRUE.

B. FALSE.

C. Nothing can be said.

D. None of the mentioned.

24. 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.

25. The number of tests required to break the Double DES algorithm are.

A. 2112.

B. 2111.

C. 2128.

D. 2119.

26. How many keys does the Triple DES algorithm use?.

A. 2.

B. 3.

C. 2 or 3.

D. 3 or 4.

27. In triple DES, the key size is ___ and meet in the middle attack takes ___ tests to break the key..

A. 2192 ,2112.

B. 21,842,111.

C. 21,682,111.

D. 21,682,112.

28. Using Differential Crypt-analysis, the minimum computations required to decipher the DES algorithm is.

A. 256.

B. 243.

C. 255.

D. 247.

29. Using Linear Crypt-analysis, the minimum computations required to decipher the DES algorithm is.

A. 248.

B. 243.

C. 256.

D. 264.

30. DES follows.

A. Hash Algorithm.

B. Caesars Cipher.

C. Feistel Cipher Structure.

D. SP Networks.

31. The DES Algorithm Cipher System consists of ____________rounds (iterations) each with a round key.

A. 12.

B. 18.

C. 9.

D. 16.

32. The DES algorithm has a key length of.

A. 128 Bits.

B. 32 Bits.

C. 64 Bits.

D. 16 Bits.

33. 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.

C. Nothing can be said.

D. None of the mentioned.

34. 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.

35. 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.

Answer= Scaling of the existing bits

36. The Initial Permutation table/matrix is of size.

A. 16×8.

B. 12×8.

C. 8×8.

D. 4×8.

37. The number of uni substitution boxes in DES after the 48 bit XOR operation are.

A. 8.

B. 4.

C. 6.

D. 12.