Network Security

Question 31

Encrypt the Message “HELLO MY DEARZ” using Transposition Cipher with

• HLLEO YM AEDRZ

• EHOLL ZYM RAED

• ELHL MDOY AZER

• ELHL DOMY ZAER

Question 32

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 33

In cryptography, the following uses transposition ciphers and the keyword is LAYER. Encrypt the following message. (Spaces are omitted during encryption) WELCOME TO NETWORK SECURITY !

• WMEKREETSILTWETCOOCYONRU!
• EETSICOOCYWMEKRONRU!LTWET
• LTWETONRU!WMEKRCOOCYEETSI
• ONRU!COOCYLTWETEETSIWMEKR

Question 34

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

• 5
• 8
• 12
• 16

Question 35

SHA-1 is a

• encryption algorithm
• decryption algorithm
• key exchange algorithm
• message digest function

Question 36

If there are N people in the world and are using secret key encryption/decryption for privacy purpose, then number of secret keys required will be:

• N
• (N - 1)
• N (N - 1) / 2
• N (N + 1) / 2

Question 37

Using public key cryptography, X adds a digital signature σ to a message M, encrypts (M,σ) and sends it to Y, where it is decrypted. Which one of the following sequence of keys is used for operations?

• Encryption : X’s private key followed by Y’s private key. Decryption : X’s public key followed by Y’s public key.
• Encryption : X’s private key followed by Y’s public key; Decryption : X’s public key followed by Y’s private key
• Encryption : X’s private key followed by Y’s public key; Decryption : Y’s private key followed by X’s public key.
• Encryption : X’s public key followed by Y’s private key; Decryption : Y’s public key followed by X’s private key.

Question 38

Anarkali digitally signs a message and sends it to Salim. Verification of the signature by Salim requires

• Anarkali’s public key.
• Salim’s public key.
• Salim’s private key.
• Anarkali’s private key.

Question 39

Suppose that everyone in a group of N people wants to communicate secretly with the N–1 others using symmetric key cryptographic system. The communication between any two persons should not be decodable by the others in the group. The number of keys required in the system as a whole to satisfy the confidentiality requirement is

• 2N
• N(N – 1)
• N(N – 1)/2
• (N – 1)²

Question 40

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