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
Answer
Answer: d [Reason:] 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
Answer
Answer: a [Reason:] 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))
Answer
Answer: b [Reason:] 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
Answer
Answer: b [Reason:] 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
Answer
Answer: c [Reason:] [(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
Answer
Answer: d [Reason:] 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
Answer
Answer: a [Reason:] 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])
Answer
Answer: a [Reason:] 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
Answer
Answer: b [Reason:] 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
Answer
Answer: d [Reason:] 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
Answer
Answer: d [Reason:] 7 bit positions are active and can affect L[0, 0] in the Iota step function.
