Question Paper: Data Compression and Encryption* Question Paper - Dec 16 - Electronics And Telecomm (Semester 7) - Mumbai University (MU)
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## Data Compression and Encryption* - Dec 16

### Electronics And Telecomm (Semester 7)

Total marks: 80
Total time: 3 Hours
INSTRUCTIONS
(1) Question No. 1 is compulsory.
(2) Attempt any three from remaining five questions.
(3) Assume suitable data wherever necessary.

• a) Explain different redundancies in data and how they are used for data compression. Also give evaluation parameters for compression techniques.
• b) What are the goals of cryptographic systems? Describe various attacks compromising these goals. 1486

• c) State Fermat's Little Theorem, Euler's Theorem in modular arithmetic. What is Euler's Totient function? Compute $\phi$(37), $\phi$(35), and $\phi$(75). 1046 1047

• d) Give an example of each: 1) Substitution cipher 2)Transposition cipher 3) Stream cipher 4) Block cipher 1488

• e) Explain extended Euclid's algorithm, and compute multiplicative inverse of 7 modulo-160.

(20 marks) 00

2(a) Explain the principle of arithmetic coding. Hence generate a decimal tag for the sequence: SWISS_MISS. Also decode the decimal tag.
(10 marks) 1011

2(b) What are the advantages of minimum variance Huffman codes over normal Huffman codes? Design a minimum variance Huffman code on the source with alphabet A={ a1, a2, a3, a4, a5 } with respective probabilities { 0.25, 0.2, 0.15, 0.3, 0.1 }.
(10 marks) 1011

3(a) Explain lossy and lossless schemes for image compression. Give an overview of JPEG-2000.
(10 marks) 1032

3(b) Explain Frequency masking, Temporal masking with respect to audio compression. Also explain how an MP-III encoder works.
(10 marks) 1483

4(a) Compute the encrypted and decrypted text using RSA algorithm for the plaintext 88. Public key is (n,e) = (187,7).
(10 marks) 1055

4(b) Perform LZ-78 compression on the following string and find the compression ratio. 10001111010111100011111100011111
(10 marks) 1011

5(a) Explain Triple-DES with two keys and the "Meet-in-the-middle-attack".
(10 marks) 1043

5(b) Consider a Diffie-Hellman scheme with a common prime q=11 and a primitive root $\alpha$=2.

• i) Show that 2 is primitive root of 11.
• ii) If user A has public key Y$_A$=9, what is A's private key X$_A$?
• iii) If user B has public key Y$_B$=3, what is the shared secret key K?
(10 marks) 1056

Q6) Write short notes on (Any Four)

• a) Digital Signatures 1060

• b) H.264 Video coding standard 1038

• c) Ethical Hacking 1070

• d) Digital Immune Systems 1068

• e) Elliptic curves for cryptography 1057

(20 marks)