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

**Q1)**Answer the following (Any five)

a) What are the measures of performances for lossy and lossless compression techniques? 1012

b) Illustrate the worst cast in LZ-77 dictionary compression technique. 1025

c) What is "frequency/auditory masking temporal mashing"? 1483

d) Which redundancies are exploited in JPEG lossy standard? Which are the processes using these redundancies?

e) State fermat's little theorem(FLT) and Euler's theorem. Illustrate with an example how FLT can be used to find modular inverse. 1046

f) Using modular arithmetic and theorems, prove that decrypted text is same as plain text in the RSA algorithm. 1055

g) What do you mean by "confusion" and "diffusion"? Which components are used in ciphers to introduce confusion and diffusion?

**2(a)**Generate a binary tag using arithmetic coding techniques for the sequence: a b a c a b b

symbol | count |
---|---|

a | 37 |

b | 38 |

c | 25 |

**2(b)**Perform LZW dictionary compression on the following text string: wabba-wabba-wabba-wabba-woo-woo-woo-woo Initial dictionary:

Index | 1 | 2 | 3 | 4 | 5 |
---|---|---|---|---|---|

Entry | - | a | b | o | w |

**3(a)**Explain MP-III audio compression standard with a neat block diagram.

**3(b)**What are different approaches for compressing an image? Explain JPEG-LS standard.

**4(a)**Explain double DES and the need for it. Also explain the "meet-in-the-middle" attack.

**4(b)**Explain any one digital signature algorithm in detail.

**5(a)**Encrypt the plain text 63 using RSA algorithm which uses prime numbers p=7 and q=11. The public key e=13. Verify that the decrypted text is same as the plain text.

**5(b)**Alice chooses her private key x=3 and Bob chooses y=6. If both of them use the primitive root g=7 for prime p=23, what is the key exchanged between Alice and Bob using diffie. Hellman Key exchange?

**Q6)**Write short notes on two.

a) Adaptive Huffman coding 1011

b) H.264 encoder-decoder 1038

c) Eliptic curve cryptography 1057

d) Intrusion detection system

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