## Data Compression and Encryption* - May 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 if necessary, with proper justification.

**Q1)**Answer the following in brief:

a) Classify data compression techniques and give example for each 1012

b) What are one way trap door functions? What is their importance in cryptography?

c) State:-i) Fermat's little theorem ii) Euler's theorem iii) Chinese Remainder theorem iv) Definition of primitive root. 1046 1047

d) What do you mean by "auditory masking" and "temporal masking"? 1483

**2(a)**A source with alphabet A= {a,b,c,d,e} with probabilities P= {0.15, 0.05, 0.25, 0.35, 0.2} respectively, calculate Standard Huffman code Minimum variance Huffman code Avg length & variance for both codes Draw binary tree for both.

**2(b)**What are private key cryptosystems? What are their advantages & disadvantages? Explain DES with neat block diagram.

**3(a)**What are dictionary based compression schemes? Explain the LZ-77 technique with an example.

**3(b)**Alice and Bob choose p=13 and q=5 as prime numbers for RSA encryption. Alice choose e=7 as public key. Derive her private key. She wants to send plain text 17 to Bob using RSA. Compute the encrypted text and show how Bob will decrypt it.

**4(a)**Explain the principle of working of MP-III audio compression standard, with a neat block diagram.

**4(b)**What are elliptic curves? Explain the "Elliptic curve Discrete Log" problem and hence explain ECC key exchange algorithm.

**5(a)**Explain any one lossless technique for image compression in detail.

**5(b)**What are digital signatures? Explain any one technique in detail.

**Q6)**Write short notes on any two:-

a) MPEG video compression standard 1036

b) Hash and MAC functions 1059

c) Digital Immune System 1068

d) Diffie-Hellman key exchange 1056