Question 1
(a)
Define Cryptography, Cryptanalysis and Cryptology.
3 Marks
(b)
Encrypt the following text with Caesar cipher: (Key=3) “Cryptography and Network Security”.
4 Marks
(c)
Discuss Public Key Cryptosystems with Applications.
7 Marks
Gujarat Technological UniversitySummer 2026 Examination
GTU 3161606 Cryptography and Network security Summer 2026 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)
Define security attack, security mechanism and security services.
3 Marks
(b)
Construct a playfair matrix with the key “moonmission” and encrypt the message “greet”.
4 Marks
(c)
Describe working of AES(Advance Encryption standard).
7 Marks
OR OPTION
(c)
Discuss Data Encryption Standard with working structure.
7 Marks
Question 3
(a)
Find 331 mod 7 using Fermat’s little theorem.
3 Marks
(b)
Find GCD(2740, 1760) using Euclidean algorithm. Show each intermediate result.
4 Marks
(c)
Compare and contrast various block cipher mode of operations.
7 Marks
OR OPTION
(a)
With the help of Euler Totient function find ø(15).
3 Marks
(b)
What is Hash Function? Explain requirements for hash functions.
4 Marks
(c)
List types of digital signature and discuss in detail Elgamal digital signature scheme.
7 Marks
Question 4
(a)
What is the difference between HTTP and HTTPS?
3 Marks
(b)
In a public key system using RSA, the ciphertext intercepted is C=10 which is sent to the user whose public key is e=5, n=35. What is the plaintext M?
4 Marks
(c)
Demonstrate the working of SSL Record Protocol with the help of necessary diagrams.
7 Marks
OR OPTION
(a)
Explain X.509 authentication service.
3 Marks
(b)
Find out inverse of 550 with extended Euclidean algorithm in Galois Field 1759.
4 Marks
(c)
Explain Diffie Hellman scheme with diagram. For Diffie- Hellman algorithm, two publically known numbers are prime number 23 and primitive root of it is 9. A selects the random integer 4 and B selects 3. Compute the public key of A and B. Also compute common secret key.
7 Marks
Question 5
(a)
Discuss MAC based on Block Ciphers.
3 Marks
(b)
Discuss various ways of Distribution of Public Keys.
4 Marks
(c)
Demonstrate the working of Kerberos Version 4 Authentication Dialogue with detailed steps.
7 Marks
OR OPTION
(a)
Illustrate Man-in-Middle attack.
3 Marks
(b)
Discuss MAC based on Hash Functions (HMAC).
4 Marks
(c)
Consider a scenario where Prachi wants to send a secret message M and her signature to Prayag. Prachi takes help of Prayag to validate her digital signature, but does not want to reveal M to Prayag. Prayag performs the necessary steps to send Prachi ‘s messages to Pramod. Draw and explain this scenario using symmetric key cryptography.
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 2026, 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.