250+ TOP MCQs on Secure Hash Algorithms (SHA) and Answers

Cryptography Multiple Choice Questions on “Secure Hash Algorithms (SHA)”.

1. The registers ‘a’ and ‘e’ involve
a) Permutation and substitution both
b) Only Permutation
c) Only substitution
d) Don’t undergo any operations

Answer: c
Clarification: The registers ‘a’ and ‘e’ undergo substitution and not permutation.

2. In SHA-512, W16 is dependent on
a) W0,W3,W7,W13
b) W3,W7,W11,W15
c) W0,W1,W9,W14
d) W0,W1,W10,W13

Answer: c
Clarification: W is defined by,
W_t = sigma^512_1(W_(t-2)) + W_(t-7) + sigma^512_0(W_(t-15)) + W_(t-16).

3. In SHA-512, W16 is dependent on
a) W63,W68,W72,W76
b) W66,W70,W71,W76
c) W63,W67,W71,W77
d) W63,W65,W71,W76

Answer: d
Clarification: W is defined by,
W_t = sigma^512_1(W_(t-2)) + W_(t-7) + sigma^512_0(W_(t-15)) + W_(t-16).

4. What is the number of operation required to come up with 2 messages having the same message digest in SHA-512?
a) 2²⁵⁶
b) 2⁵¹²
c) 2¹⁰²⁴
d) 2¹²⁸

Answer: a
Clarification: The difficulty of coming up with 2 messages having the same message digest is on the order of 2²⁵⁶.

5. The underlying structure of the SHA-3 algorithm is referred to as
a) Texture construction
b) Layer construction
c) Sponge construction
d) Cement construction

Answer: c
Clarification: The underlying structure of the SHA-3 algorithm is referred to as Sponge construction.

6. SHA-3 allows variable length input and output.
a) True
b) False

Answer: a
Clarification: SHA-3 does allow variable length input and output.

7. Multi-rate padding is denoted by
a) 10*
b) 10*1
c) 10*1*
d) 0*1

Answer: b
Clarification: Multi-rate padding appends a single bit 1 followed by the minimum number of 0s followed by a single bit 1 such that the length of the result is a multiple of the block length.

8. In SHA-3, if the desired output is l bits, then j blocks are produced, such that
a) (j-1) x r < l <= (j) x r
b) (j) x r< l <= (j+1) x r
c) (j-1) x r < l <= (j+1) x r
d) (j+1) x r < l <= (j+2) x r

Answer: a
Clarification: (j-1) x r < l <= j x r, is th correct option; ’l’ should lie between (j-1) x r and j x r.

9. In the sponge construction, the value ‘c’ is known as
a) constant
b) capacity
c) construct
d) closure

Answer: b
Clarification: The value ‘c’ is referred to as capacity.

10. The larger the value of ‘r’, the lesser the rate at which message bits are processed by the sponge construction.
a) True
b) False

Answer: b
Clarification: The larger the value of ‘r’, the greater the rate at which message bits are processed by the sponge construction. ‘r’ is referred to as bitrate.

11. We can trade security for speed by
a) decreasing ‘c’ and increasing ‘r’
b) increasing ‘c’ and decreasing ‘r’
c) decreasing both ‘c’ and ‘r’
d) increasing both ‘c’ and ‘r’

Answer: b
Clarification: We can trade security for speed by increasing capacity and decreasing bitrate.

12. The default values for Keccak f are
a) c =1024 and r =576
b) c =786 and r =832
c) c =512 and r =1088
d) c =512 and r =832

Answer: c
Clarification: The default value for the Keccak function always has c + r = 1600.