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