Network Security

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Question 1

The minimum positive integer p such that 3p modulo 17 = 1 is

  • 5

  • 8

  • 12

  • 16

Question 2

In the RSA public key cryptosystem, the private and public keys are (e, n) and (d, n) respectively, where n = p*q and p and q are large primes. Besides, n is public and p and q are private. Let M be an integer such that 0 < M < n and f(n) = (p- 1)(q-1). Now consider the following equations. 

 
I.  M’= Me mod n
    M = (M’)d mod n 

II.  ed ≡ 1 mod n 

III. ed ≡ 1 mod f(n)

IV. M’= Me mod f(n)
    M = (M’)d mod f(n)

Which of the above equations correctly represent RSA cryptosystem?

  • I and II

  • I and III

  • II and IV

  • III and IV

Question 3

A firewall is to be configured to allow hosts in a private network to freely open TCP connections and send packets on open connections. However, it will only allow external hosts to send packets on existing open TCP connections or connections that are being opened (by internal hosts) but not allow them to open TCP connections to hosts in the private network. To achieve this the minimum capability of the firewall should be that of

  • A combinational circuit

  • A finite automaton

  • A pushdown automaton with one stack

  • A pushdown automaton with two stacks

Question 4

A Trojan horse is
  • A program that performs a legitimate function that is known to an operating system or its user and also has a hidden component that can be used for nefarious purposes like attacks on message security or impersonation.
  • A piece of code that can attach itself to other programs in the system and spread to other systems when programs are copied or transferred.
  • A program that spreads to other computer systems by exploiting security holes like weaknesses in facilities for creation of remote processes
  • All of the above

Question 5

A public key encryption system

  • allows anyone to decode the transmissions

  • allows only the correct sender to decode the data

  • allows only the correct receiver to decode the data

  • does not encode the data before transmitting it

Question 6

A message "COMPUTERNETWORK" encrypted (ignore quotes) using columnar transposition cipher with a key "LAYER". The encrypted message is :

  • CTTOEWMROPNRUEK

  • MROUEKCTTPNROEW

  • OEWPNRCTTUEKMRO

  • UEKPNRMROOEWCTT

Question 7

The standard for certificates used on internet is

  • X.25

  • X.301

  • X.409

  • X.509

Question 8

Hashed message is signed by a sender using his

  • his public key

  • his private key

  • receiver’s public key

  • receiver’s private key

Question 9

How many distinct stages are there in DES algorithm, which is parameterized by a 56-bit key?
  • 16
  • 17
  • 18
  • 19

Question 10

Which one of the following is true for asymmetric-key cryptography?
  • Private key is kept by the receiver and public key is announced to the public.
  • Public key is kept by the receiver and private key is announced to the public.
  • Both private key and public key are kept by the receiver.
  • Both private key and public key are announced to the public.

There are 40 questions to complete.

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