This set of Cryptography Multiple Choice Questions & Answers (MCQs) focuses on “Secure Hash Algorithms (SHA) – 2”.

1. The registers ‘a’ and ‘e’ involve

a) Permutation and substitution both

b) Only Permutation

c) Only substitution

d) Don’t undergo any operations

View Answer

Explanation: 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

View Answer

Explanation: 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

View Answer

Explanation: 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) 2^{256}

b) 2^{512}

c) 2^{1024}

d) 2^{128}

View Answer

Explanation: The difficulty of coming up with 2 messages having the same message digest is on the order of 2

^{256}.

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

View Answer

Explanation: 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

View Answer

Explanation: 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

View Answer

Explanation: 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

View Answer

Explanation: (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

View Answer

Explanation: 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

View Answer

Explanation: 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’

View Answer

Explanation: 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

View Answer

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

**Sanfoundry Global Education & Learning Series – Cryptography and Network Security.**

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