CS-703-A Cryptography and Information Security - Nov 2022 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aHow do you convert a block cipher into a stream cipher by using the Cipher Feedback (CFB) mode? Explain.
   How to answer

   • Define block cipher vs stream cipher
   • CFB mode operation with shift register and encryption of IV
   • How s-bit feedback converts block cipher to stream
   • Diagram of CFB encryption/decryption
2. 7 Marks
   bExplain the concept of Cryptanalysis and Brute force attack.
   How to answer

   • Define cryptanalysis and its goal
   • Types of cryptanalytic attacks briefly
   • Define brute-force attack and key search
   • Comparison of effort and countermeasures
3. 7 Marks
   aExplain the steps for the Key Generation of DES algorithms.
   How to answer

   • Initial 64-bit key with parity, PC-1 to 56 bits
   • Split into C and D halves, left shifts per round schedule
   • PC-2 compression to 48-bit round keys
   • Generation of 16 round keys for DES rounds
4. 7 Marks
   bGive the structure of AES. Explain how Encryption/ Decryption is done in AES.
   How to answer

   • AES parameters: 128-bit block, Nk/Nr by key size
   • State array and key expansion overview
   • Four round transformations: SubBytes, ShiftRows, MixColumns, AddRoundKey
   • Encryption vs decryption flow with inverse operations
5. 7 Marks
   aState Chinese Remainder theorem and find X for the given set of congruent equations using CRT. $$X=1(mod\ 5)$$ $$X=2(mod\ 7)$$ $$X=3(mod\ 9)$$ $$X=4(mod\ 11)$$
   How to answer

   • Statement of Chinese Remainder Theorem for coprime moduli
   • Compute M, Mi and modular inverses
   • Apply formula $X = \sum a_i M_i y_i \mod M$
   • Verify solution for given congruences
6. 7 Marks
   bExplain in short different method of distribution of public key management.
   How to answer

   • Need for public-key distribution
   • Public announcement, directory, authority methods
   • Certificates and PKI briefly
   • Comparison of security and overhead
7. 7 Marks
   aUser A and B exchange the key using Diffie-Hellman algorithm. Assume $a = 5, q = 11, X_A = 2$ and $X_B = 3$. Find $Y_A, Y_B$ and $K$.
   How to answer

   • Diffie-Hellman formulas $Y_A = \alpha^{X_A} \mod q$
   • $Y_B$ calculation with given values
   • Shared secret $K = Y_B^{X_A} = Y_A^{X_B} \mod q$
   • Numeric result verification
8. 7 Marks
   bWhat is MD5? Explain MD5 with neat and clean diagram.
   How to answer

   • Define MD5 as 128-bit message digest
   • Padding, append length, 4 rounds with functions
   • Processing of 512-bit blocks and registers
   • Neat labelled diagram of MD5 operation
9. 7 Marks
   aExplain the Secure Hash Algorithm (SHA) with their Merit and Demerit.
   How to answer

   • Define SHA family and variants
   • General SHA operation and compression
   • Merits: security, standard, applications
   • Demerits: length extension, speed, SHA-0/1 weaknesses
10. 7 Marks
    bWhy does PGP compress the message? What are the reasons for compressing the signature but before encryption?
    How to answer

    • PGP services and need for compression
    • Reasons: save space, transmission time, security against cryptanalysis
    • Why sign then compress then encrypt order
    • Effect on signature and encryption strength
11. 7 Marks
    aExplain the sequence of steps used in Secure Socket Layer handshake Protocol for establishing a new session. Draw a diagram which shows the action of Handshake Protocol. https://www.rgpvonline.com
    How to answer

    • Purpose of SSL/TLS handshake for new session
    • Sequence: hello, certificate, key exchange, finished
    • Action diagram showing client-server messages
    • Session establishment and parameters
12. 7 Marks
    bWhat is a Honeypot? Explain types of honeypot.
    How to answer

    • Define honeypot as decoy system
    • Low vs high interaction honeypots
    • Production vs research types
    • Uses and limitations
13. 7 Marks
    aExplain in short different types of DoS Attack Understanding Tools.
    How to answer

    • Define DoS attack and impact
    • Types: flooding, SYN, Smurf, DDoS tools
    • Understanding/analysis tools examples
    • Mitigation overview
14. 7 Marks
    bExplain in short different types of Trojans detection tools.
    How to answer

    • Define Trojan and detection need
    • Types of detection tools: antivirus, behavior, sandbox
    • Examples of tools and working
    • Prevention measures
15. 14 Marks
    Write short notes on following(Any two):

    1. a)Firewall and its types.
    2. b)Digital Signature Standard (DSS)
    3. c)Triple DES
    4. d)Schnorr Identification Scheme with the discrete logarithm
    How to answer

    • Select any two topics with definition
    • Working principle and key steps/diagram
    • Applications, advantages/limitations
    • Concluding comparison or example