Model Question Paper CST 393 Cryptographic Algorithms


APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY

FIFTH SEMESTER B.TECH DEGREE EXAMINATION(HONORS), MONTH &

YEAR

Course Code: CST 393

Course Name: Cryptographic Algorithms

Max.Marks:100 Duration: 3 Hours

PART A


Answer all Questions. Each question carries 3 Marks

1. State the two approaches in attacking a cipher.
2. Define Substitution Cipher. Encrypt using one time pad M = HONORS and K = CIPHER.
3. Specify the purpose of S-Boxes in Data Encryption Standard (DES).
4. Differentiate between diffusion and confusion.
5. Perform encryption using RSA Algorithm for the following p=7; q=11; e=13;M=5
6. Is Diffie-Hellman key exchange protocol vulnerable? Justify.
7. List the techniques for distribution of public keys.
8. Define a certificate authority and its relation to public key cryptography.
9. Distinguish between integrity and message authentication.
10. What types of attacks are addressed by message authentication?
Part B
(Answer any one question from each module. Each question carries 14 Marks)
11. (a) With a neat sketch, Explain OSI Security architecture model.
                                                                                                                            (8)
(b) How does link encryption differ from end-to-end encryption? Explain.
                                                                                                                            (6)
OR
12. (a) Encrypt the text “cryptography” using the Hill Cipher with the key

5 7
9 4
. Show the calculations.
                                                                                                                          (8)
(b) Illustrate the steps involved in encrypting a plain text using playfair cipher
with an example.                                                                                               (6)

13. (a) With a neat sketch, explain a single round in DES.                            (10)
(b)Explain encryption and decryption using 2 keys and 3 keys of triple DES.                                                                                                                                                                    (4)
                                                    OR
14. (a) Explain the block cipher modes i) Cipher feedback mode ii) Output
feedback mode.                                                                                                (8)
(b) Describe the four types of transformations in AES.                                 (6)

15. (a) Write an algorithm for generating public and private key using Elliptical
curve cryptography.
(b) The equation y2=x3 +x+1, the calculation is done modulo 13. Add two
points R= P+Q, where P= (4,2) and Q= (10,6).

OR
16. User A and B use the Diffie-Hellman key exchange technique with a common prime q=71 and primitive root alpha=7.
primitive root alpha=7.
(a) If user A has private key XA =3, What is A’s public key YA? (7)
(b) If user B has private key XB =6, What is A’s public key YB? (7)

17. (a) Define a session key and show how a KDC can create can create a session key between Alice and Bob. (7)
(b) What are the requirements for the use of a public-key certificate scheme? (7)
OR
18. (a) What are the core components of a PKI? Briefly describe each component. (8)
(b) Describe the following (i) Updating keys (ii) Compromised Keys. (6)



19. (a) Describe how SHA-512 logic produce message digest (10)
(b) Distinguish between HMAC and CMAC (4)
OR
20. (a) Specify the format for X.509 certificate. Explain the steps required to obtain user’s certificate. (7)
(b) With suitable block diagrams, explain the types of functions that may be used to produce an authenticator. (8 )

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