Question 1
(a)
Define the following
i)Denial of Service
ii)Masquerade
iii)Non-repudiation
3 Marks
(b)
Differentiate between Brute force and cryptanalysis.
4 Marks
(c)
What are the various types of security attacks? Explain them in detail.
7 Marks
Gujarat Technological UniversitySummer 2025 Examination
GTU 3161606 Cryptography and Network security Summer 2025 Paper Solution & PDF
B.E. · IT Engineering · Semester 6 · Subject Code: 3161606
Total Marks70 MarksExternal theory exam
Passing Marks23 Marks33% minimum cutoff
Exam Duration2.5 Hours10:30 AM – 1:00 PM
Paper Structure5 QuestionsWith internal OR choices
Question 2
(a)
Use play fair cipher technique to encrypt the message “beauty lies in the eyes of a beholder” with the key “Monarchy”
3 Marks
(b)
Hill cipher key is |17 17 5 | |21 8 21 | |2 2 19 | Encrypt “paymoremoney”
4 Marks
(c)
Distinguish between transposition and substitution methods with examples
7 Marks
OR OPTION
(c)
List down various modes of operations of block cipher and Explain ECB, OFB and COUNTER modes briefly.
7 Marks
Question 3
(a)
On what criteria the strength of DES algorithm depends? Explain with reason.
3 Marks
(b)
Compare public key cryptography with private key cryptography in detail.
4 Marks
(c)
Explain Key Expansion in AES algorithm.
7 Marks
OR OPTION
(a)
Explain meet in the middle attack in DES.
3 Marks
(b)
Explain timing attack in RSA.
4 Marks
(c)
Explain single round function in DES algorithm.
7 Marks
Question 4
(a)
What is SHA? Why it is needed in cryptography? Explain.
3 Marks
(b)
In RSA system, the public key of a user is e=7, p=17, q=11. What is the private key of this user? Also decrypt the message 11 using private key.
4 Marks
(c)
Explain Diffie Hellman algorithm with example.
7 Marks
OR OPTION
(a)
Define unconditionally secure cipher? Why one-time pad cipher is unconditionally secure?
3 Marks
(b)
Write the Euclid’s algorithm and show the steps of Euclid’s algorithm to find gcd(1970,1066).
4 Marks
(c)
Define KDC? Explain key distribution with diagram.
7 Marks
Question 5
(a)
Explain X.509 authentication service in brief.
3 Marks
(b)
Explain Secure Socket Layer.
4 Marks
(c)
Explain SHA1 hashing algorithm in detail.
7 Marks
OR OPTION
(a)
Differentiate MAC and Hash function?
3 Marks
(b)
Explain Digital signature. What requirements should a Digital signature scheme satisfy?
4 Marks
(c)
Explain Kerberos protocol in details.
7 Marks
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About this Examination Paper & Attribution
Official Gujarat Technological University (GTU) examination paper and step-by-step solutions for Cryptography and Network security (Summer 2025, B.E. · IT Engineering, Sem 6). Features complete 70-mark regular & remedial examination pattern, official marking distribution across all 5 questions, and direct 1-click official PDF download.
Transcribed for student exam preparation from Gujarat Technological University official examination archives. Questions, syllabus guidelines, and curriculum marking schemes remain the intellectual property of Gujarat Technological University.