Practice_Exam

Question 1

It is said that DES permutations do not add to security, but just increase brute-force attack time. This is because

a. The initial and final permutations are inverses of each other.
b. Permutations are derived from a subset of the keys.
c. Permutations are not derived from keys – they are fixed.
d. The permutations are performed in each round.

Answer 1

C

Question 2

A permutation and its inverse are the same. The permutation must be

a. (4, 3, 2, 1)
b. (1, 2, 3, 4)
c. Both (a) and (b)
d. Neither (a) nor (b)

Answer 2

C

Question 3

One advantage of electronic code book over cipher block chaining is

a. It is more secure
b. It uses less number of keys
c. Blocks can be encrypted in parallel

Answer 3

C

Question 4

What is the correct form of representing 76 mod 13?

a. (72 mod 13)(73 mod 13)
b. (72 mod 13)(72 mod 13)(72 mod 13)
c. ((72 mod 13)(73 mod 13)) mod 13
d. ((72 mod 13)(72 mod 13)(72 mod 13)) mod 13

Answer 4

D

Question 5

What is/are the security goals attainable by digital signatures?

a. Integrity
b. Authentication
c. Access Control
d. Integrity and Authentication

Answer 5

D

Question 6

What is the advantage of private key encryption over public key encryption?

a. Provides integrity and authentication
b. Uses less number of keys in a group communication scenario
c. Can be implemented in software
d. Faster than public key encryption

Answer 6

D

Question 7

In a three-way handshake key exchange, the following is true:

a. The server authenticates the client, but not vice versa.
b. The client authenticates the server, but not vice versa.
c. The client and the server both authenticate each other.
d. The client and the server do not authenticate each other.

Answer 7

D

Question 8

What is the most significant feature of the Diffie Hellman exchange?

a. Fast key exchange
b. Easy to implement
c. Key exchange among a group of nodes
d. Keys are never exchanged, but are generated

Answer 8

D

Question 9

A digital signature is produced by the following procedure:

a. Hash the message M and encrypt it with sender’s public key
b. Hash the message M and encrypt it with sender’s private key
c. Hash the message M and encrypt it with recipient’s public key
d. Hash the message M and encrypt it with recipient’s private key

Answer 9

B

Question 10

The protocol used for authentication in WiFi Protected Access Version 1 (WPA1) is

a. TKIP
b. WEP encapsulation
c. IEEE 802.1x
d. CCMP

Answer 10

C

Question 11

The least number of messages required for a Diffie Hellman exchange between two parties is

a. One
b. Two
c. Three
d. Four

Answer 11

B

Question 12

You can get back a message M with the following procedure

a. Encrypt M with Alice’s public key and decrypt it with Alice’s private key
b. Encrypt M with Bob’s private key and decrypt it with Bob’s public key
c. Encrypt M with Bob’s public key and decrypt it with Alice’s private key
d. Either (a) and (b)
e. Either (b) and (c)

Answer 12

D

Question 13

One of the advantages of stream ciphers over block ciphers is

a. It is much more secure
b. The standards are well-defined c. Errors do not propagate
d. It is more scalable

Answer 13

C

Question 14

What is the total number of keys required if private key cryptography is used? Instead of 5 nodes, if the number of nodes is n, what is the total number of keys required with private key cryptography?

Answer 14

n(n-1)/2

Question 15

What is the total number of keys required if public key cryptography is used? Instead of 5 nodes, if the number of nodes is n, what is the total number of keys required with public key cryptography?

Answer 15

2n

Question 16

If the prime numbers p and q are 13 and 19, respectively, in the RSA technique, derive the public and private keys. Also show how a message m = 6 will be encrypted. [formula]

Answer 16

• ed mod (p-1) (q-1) = 1
• e prime and small than n
• n = pq

Question 17

Calculate 5 11 mod 13 without using a calculator. (show steps).

Answer 17

511 mod 13 = ((52 mod 13)(52 mod 13)(52 mod 13)(52 mod 13)(52 mod 13)(5 mod 13)) mod 13

Question 18

lice wishes to use Diffie-Hellman exchange to share a secret key with Bob. She publishes the following ad. in the Chronicle Herald:
Dear Bob, My p = 11 and my g = 7 Cheers,Alice
Take Bob and Alice through the Diffie Hellman exchange steps and derive the secret number.

Answer 18

SA = 3
SB = 5

Ta = g^SAmodp
Tb = g^SBmodp

Tb^SA mod p
Ta^SB mod p

Question 19

What is AH transport/tunnel

Answer 19

IP/DATA
IP/AH/DATA
IP/AH/IP/DATA

Question 20

What is ESP transport/tunnel

Answer 20

IP/DATA
IP/ESPH/DATA/ESPT
IP/ESPH/IP/DATA/ESPT

Question 21

During one security association of IPSec, how many DIffie Hellman exchanges are performed? What are the resulting keys used for?

Answer 21

There are two Diffie Hellman exchanges during one secure association of IPSec. During the first phase, a DH exchange is done to establish the master key. This master key is used to authenticate and certify the two parties. Using this master key, one more DH exchange done in a secure manner. This establishes the session key. The session key is used for transfer of messages using private key encryption.

Question 22

Identify five weaknesses in WEP.

Answer 22

1. IV is sent in plaintext.
2. Key is shared and static.
3. Key size is 40 bits or 104 bits (not 64 or 128 bits as claimed). 4. CRC is used for message integrity.
4. Weak authentication

Question 23

List the following protocols in IEEE 802.11 in increasing levels of security:

a. TKIP
b. CCMP
c. SSID
d. WEP

Answer 23

Answer: 
SSID 
WEP 
TKIP 
CCMP

Question 24

What is a dual signature? Explain by means of a diagram how it is derived in the context of Secure Electronic Transaction (SET).

Answer 24

Order Information (OI) is hashed to get OIMD
Payment Information (PI) is hashed to get PIMD
OIMD and PIMD are concatenated to get POMD
POMD is signed by the customer’s private key to get the Dual Signature.

Question 25

What are the three parties involved in the authentication and key management procedure in 3G cellular networks?

Answer 25

USIM
VLR
AUC

Question 26

What are the five phases of a security plan?

Answer 26

Inspection
Protection
Detection
Reaction
Reflection

Question 27

Define Risk Exposure

Answer 27

Risk Exposure = Risk Impact X Risk Probability

Question 28

An IT company PoorCo. has two database servers DB1 and DB2 The following numbers indicate their costs, risks and cost of securing each infrastructure.

Answer 28

(RE_before - RE_after) / cost of sec