This set of Cryptography Multiple Choice Questions & Answers (MCQs) focuses on “Secure Hash Algorithms (SHA)”.
1. In the Theta step function, which is a substitution step, each bit value changes. Each bit is dependent on _________ other bits for its new value.
a) 13
b) 4
c) 7
d) 11
View Answer
Explanation: In the theta function each bit is dependent on 11 other bits.
2. Which step function provides most amount of diffusion for the Keccak iteration step?
a) Theta
b) Rho
c) Pi
d) Chi
View Answer
Explanation: The Theta step function provides the most significant amount of diffusion for the SHA-3.
3. The Pi step function can be written as-
a) (x, y) × (y, (x + y))
b) (x, y) × (y, (2x + 3y))
c) (x, 2y) × (y, (2x + 3y))
d) (x, 2y) × (y, (x + y))
View Answer
Explanation: The Pi function is represented as (x, y) × (y, (2x + 3y)) in terms of matrix multiplication.
4. The CHI step involves which of the following gate operations?
a) AND and NAND
b) AND and XOR
c) XOR and NAND
d) XOR and XNOR
View Answer
Explanation: The CHI step uses the AND and XOR operation.
5. Which matrix is used in the Rho/ Pi steps?
a) [(1 2 | 3 4)]t
b) [(0 2 | 1 4)]t
c) [(0 1 | 2 3)]t
d) [(1 3 | 2 4)]t
View Answer
Explanation: [(0 1 | 2 3)]t is used to find the new (x, y) co-ordinates in the Rho/Pi function.
6. What are the new co-ordinates for (x, y) in the Rho step for t =3?
a) (1, 7)
b) (1, 4)
c) (3, 2)
d) none of the mentioned
View Answer
Explanation: The correct answer is (1, 7) mod 5 which is (1, 2).
[(0 1 | 2 3)]3 + (1 , 0 ) gives the answer.
7. The Rho function is defined as : a[x, y, z] ← a[x, y, z-g(t)], where g(t) is defined as
a) (t+1)(t+2)/2
b) (t+1)(t-2)/2
c) (t-1)(t-2)/2
d) (t-1)(t+2)/2
View Answer
Explanation: g(t) is defined as (t+1)(t+2)/2.
8. The Chi function is defined as
a) a[x] ← a[x] XOR ( a[x + 1]XOR 1) AND a[x+2])
b) a[x] ← a[x] AND ( a[x + 1]XOR 1) AND a[x+2])
c) a[x] ← a[x] AND ( a[x + 1] XOR a[x+2])
d) a[x] ← a[x] XOR ( a[x + 1] AND a[x+2])
View Answer
Explanation: The Chi function is defined as a[x] ← a[x] XOR ( a[x + 1]XOR 1) AND a[x+2]).
9. In SHA-3, the Iota step function has a round constant which only works on the last lane.
a) True
b) False
View Answer
Explanation: The Iota step function has a round constant which works on the first lane of the internal state array.
10. Which is the only step function that provides non-linear mapping?
a) Theta
b) Rho
c) Pi
d) Chi
View Answer
Explanation: The Chi function provides non-linear mapping. Without it SHA-3 would be linear.
11. How many bit positions are active and can affect L[0, 0] in the Iota step function?
a) 8
b) 12
c) 6
d) 7
View Answer
Explanation: 7 bit positions are active and can affect L[0, 0] in the Iota step function.
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