Question Paper: Data Compression and Encryption* Question Paper - Dec 17 - Electronics And Telecomm (Semester 7) - Mumbai University (MU)

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## Data Compression and Encryption* - Dec 17

### 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 with proper justification.

**1(a)**What is the significance of modeling and coding in data compression?

**1(b)**What are the goals of cryptography? Explain any one in detail.

**1(c)**List techniques used for lossless image compression.

**1(d)**Solve the following.

- i) 4$^{-1}$mod 55
- ii) 3$^{144}$mod 13
- iii) 6$^{-1}$mod 17
- iv) Euler's totient function $\phi$(49)

**2(a)**What is 'frequency' and 'temporal' masking? Explain how it is used and implemented in MP3 audio compression.

**2(b)**Explain Diffie Hellman Key exchange with the help of an example.

**3(a)**Explain standard JPEG with neat block diagram. What are advantages of JPEG 2000 over standard JPEG? Justify the use of the DCT in JPEG?

**3(b)**Explain RSA in detail and also discuss attacks on RSA.

**4(a)**State following theorems with their applications in cryptography

- i) Fermat's Theorem
- ii) Euler's Theorem
- iii) Chinese Remainder Theorem.

**4(b)**Explain Hash and MAC functions with their role in cryptography.

**5(a)**Consider the probabilities p(a)=0.2, p(b)=0.3, p(c)=0.1, p(d)=0.4. Encode and decode the sequence

*abcad*using arithmetic coding technique.

**5(b)**What is Motion compensation and Motion Estimation in video compression? Explain how they are used in MPEG video compression with appropriate block diagram.

**6(a)**Encode and decode the sequence 'abbacbbabbacc' using LZ78. Compare LZ77 and LZ78.

**6(b)**Write short notes(Any two)

i) $\mu$ Law and A Law Companding 1028

ii) Fire walls 1066

iii) Intruders and viruses 1065