Hash Functions Based on Cipher Block Chaining
1. What is the effectiveness of an n-bit hash value?
a) 2n
b) 2-n
c) 22n
d) 2-2n
2. What is the effectiveness of a 128 bit hash value?
a) 2-64
b) 264
c) 2-112
d) 2-128
3. We define collision as: A collision occurs if we have x=y and H(x) = H(y).
a) True
b) False
4. Consider the following properties
Variable Input size
Fixed Output size
Efficiency
Pre image resistant
Second Pre image Resistant
Collision resistant
Pseudo randomness
A has function that satisfies the first _______ properties in the above table is referred to as a
weak hash function.
a) 5
b) 4
c) 3
d) 2
5. The second pre-image resistant property is
a) It is computationally infeasible to find any pair (x, y) such that H(x) = H(y)
b) For any given block x, it is computationally infeasible to find y not equal to x, with H(y) =
H(x)
c) For any given hash value h it is computationally infeasible to find y such that H(y) = h
d) None of the mentioned
6. A function that is second pre-image resistant is also collision resistant.
a) True
b) False
7. For an m-bit value, the adversary would have to try ____________ values to generates a
given hash value h.
a) 2m
b) 2(m-1)
c) 2(m/2)
d) (2m) 1
8. For an m bit hash value, if we pick data blocks at random we can expect to find two data
blocks with the same hash value within ____ attempts.
a) 2m
b) 2(m-1)
c) 2(m/2)
d) (2m) 1
9. Which attack requires the least effort/computations?
a) Pre-image
b) Second Pre-image
c) Collision
d) All required the same effort

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