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) 2256
b) 2512
c) 21024
d) 2128
View Answer
Explanation: 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
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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