(AUTONOMOUS)
B. Tech VII Semester Supplementary Examinations, May 2018
(Regulations: VCE-R11/11A)
NETWORK SECURITY AND CRYPTOGRAPHY
(Information Technology)
Date: 17 May, 2018 AN Time: 3 hours Max Marks: 75
Answer ONE question from each Unit
All Questions Carry Equal Marks
Unit I
1. Define security 'services', attacks', and 'mechanisms'. Also describe the classification of
security services and attacks briefly.
10M
By using playfair cipher technique, find cipher text for the message 'substitutioncipher'
with k e y w o r d " C R Y P T O G R A P H Y".
5M
2. Explain the concept of computer security with the help of CIA triad. 7M
In Vigenere cipher, the key is a stream of random numbers between 0 and 25. For
example, if the key is 3 19 5…, then the first letter of plaintext is encrypted with a shift
of 3 letters, the second with a shift of 19 letters, the third with a shift of 5 letter, and so
on.
i. Encrypt the plaintext "sendmoremoney" with the key stream 9 0 1 23 15 21 14 11
11 2 8 9 7.
ii. Using the ciphertext produced in part find a key so that the cipher text decrypts to
t h e plaintext "cashnotneeded".
8M
Unit II
3. What are the strength's of Data encryption standard (DES).In brief explain the key
generation Procedure in DES?
7M
Give an overview of the two most powerful and promising cryptanalysis technique.
8M
4. Explain the factors used by NIST to evaluate AES algorithm. 7M
With a neat block diagram explain the overall structure of AES encryption and decryption.
8M
Unit III
5. Compare and contrast the DSS approach for generating digital signature with RSA
approach. State and prove Digital Signature Algorithm (DSA).
9M
In a public-key crypto system using RSA, you intercept the ciphertext C 18 sent to a
user whose public key is e n 35. What is the plaintext
6M
6. Describe how public-key distribution of secret keys helps in establishing a session key.
Show that it is vulnerable to an active attack and discuss a method that provides both
confidentiality and authentication.
9M
List the properties of hash function and explain the significance of each.
6M
Unit IV
7. Explain PGP message generation and reception. 8M
List the limitations of SMTP/822 scheme.
7M
8. Explain the applications and benefits of IP security. 8M
Write a short note on Encapsulating security Payload.
7M
Unit V
9. How secure socket layer Record Protocol provides confidentiality and message integrity?
Explain the steps involved.
8M
Describe the intrusion detection technique used to defend a collection of hosts supported
by an internetwork.
7M
10. How viruses are classified? Explain each type in brief. 8M
What is meant by a firewall? Discuss various types of firewalls. 7M