BE-VII/New/PEC-IT 712(d)/R/2021-22/UIT/BU
B.E Odd Semester (7th) Examinations 2021-22
Subject: Cryptography and Network Security
Code: PEC-IT 712(d)
Time: 3 Hours
Full Marks: 70
Instructions: Answer any four from Group A and any five from Group B
Answer all part of a question in same place.
Send this answer script to the mail id: uit.pecit712d.newit.reg@gmail.com
Group A (Answer any four from Q. no 1 to 6)
4×5=20
Q.NO.
1.
QUESTIONS
What is Zm? How does it differ from Zm*?
MARKS
5
2.
Explain a scheme used to ensure the Authenticity of Source and Message
as well as Confidentiality.
5
3.
Which parameters and design choices determine the actual algorithm of a
Feistel cipher?
5
4.
Describe Kerberos authentication steps between two communicating
parties.
5
5.
What information is used by a typical packet-filtering router and
what are the weaknesses of a packet-filtering router?
5
6.
List and briefly define different types of cryptanalytic attacks.
5
Group B (Answer any five from Q. no 7 to 13)
7.
8.
5×10=50
a) Find the multiplicative inverse pairs of Z₁₀
b) Select that are congruent modulo 13 in the set {17,28, -9, 51,56}.
c) Determine if matrix B is multiplicative inverse of matrix A modulo 7.
A=|5 1|
B=|1 5 |
|2 4|
|3 3 |
a) Obtain the value of X that satisfies the following four congruences:
X ≡ 4 (mod 10)
X ≡ 6 (mod 13)
X ≡ 4 (mod 7)
X ≡ 2 (mod 11)
b) An RSA cryptosystem has p = 3, q = 7
i) find decryption key (choose the encryption key on your own)
ii) encrypt 11
iii) decrypt 2
Semester: 7th
Year: 2021-22
Subject Code: PEC-IT 712(d)
3+3+4
4+6
BE-VII/New/PEC-IT 712(d)/R/2021-22/UIT/BU
B.E Odd Semester (7th) Examinations 2021-22
Subject: Cryptography and Network Security
Code: PEC-IT 712(d)
Time: 3 Hours
Full Marks: 70
Instructions: Answer any four from Group A and any five from Group B
Answer all part of a question in same place.
Send this answer script to the mail id: uit.pecit712d.newit.reg@gmail.com
9.
a) List the categories of security services in network security.
b) Suppose that Chess-king organizes online chess tournaments. He
announces the first round of live match between grandmasters Alice
and Bob the first round is free for all viewers, but the viewers must
register for watching the game on their computers. The grandmasters
make chess moves on their computers connected to the Internet
Identify the security services required for the communication between
i) a grandmaster and the game server
ii) a viewer and the game server
Justify your answer
Explain with diagram the Key Expansion procedure in AES.
10.
11.
a) List different attacks on Digital Signature.
b) Explain Diffie-Hellman key exchange algorithm and compute the
half-keys and shared secret key with the following parameters.
P = 23, g = 5, a = 4, b = 3
3+7
10
3+7
12.
a) DES ensures confusion and diffusion. Explain.
b) What is the idea behind meet-in-the-middle-attack?
c) How can the same key be reused in triple DES?
4+3+4
13.
a) Name the four key steps in the creation of a digital certificate.
b) Consider a situation: an attacker (A) creates a certificate, puts a
genuine organization name (say bank B) and he puts the attacker’s
own public key. You get this certificate from the attacker, without
knowing that the attacker is sending it. You think it is from bank B.
How can this be prevented or resolved? Explain with diagram.
4+6
Semester: 7th
Year: 2021-22
Subject Code: PEC-IT 712(d)