Data Communication and Computer Networks MCQ - Computer Network

56 Given a hash table T with 25 slots that stores 2000 elements, the load factor α for T is __________

load factor = (no. of elements) / (no. of table slots) = 2000/25 = 80

57 Let h be a cryptographic hash function. Which of the following is not a property of h?

A
Given hash y, it should be computationally infeasible to find x such that y = h(x).
B
Given hash y and a message x such that y = h(x), it should be computationally infeasible to find x'≠ x such that h(x') = h(x) = y.
C
Given hash y, it should be easy to find x such that y = h(x).
D
It should be computationally infeasible to find x', x such that h(x') = h(x)

58 Both MD4 and MD5 produce a _____ bit message digest whereas SHA-1 produces a _____ bit message digest.

59 Let h be a hash chosen uniformly at random from a universal set H of hash functions. Suppose hashing n keys into m slots in table T. Then for a given key x, E(Number of collision with x) (Where E(x) denotes the expectation of X).

60 In Digital Signature Standard Algorithm suppose p = 283, q = 47, g = 60. Let user's private key a = 24 and random value chosen be k = 15. Consider a message M with message digest h = Hash (M).
Then the signature (r, s) = _______

INPUT: Domain parameters (p=283,q=47,g=60)
INPUT: user's private key, a=24
INPUT: Message M with message digest h=Hash(M)=41.
user chooses a random k=15 in the range [1,q−1]
user computes X=gkmodp=6015mod283=207 and
r=Xmodq=207mod47=19.
r≠0 so continue.
user computes k−1modq=15−1mod47=22.
user computes h=Hash(M)=41.
user computes s=k−1(h+ar)modq=22(41+24⋅19)mod47=30.
s≠0 so continue.
user's issues the message M and signature (r,s)=(19,30).