## Information Theory and Coding - Dec 2015

### Information Technology (Semester 4)

TOTAL MARKS: 80

TOTAL TIME: 3 HOURS
(1) Question 1 is compulsory.

(2) Attempt any **three** from the remaining questions.

(3) Assume data if required.

(4) Figures to the right indicate full marks.
**1 (a)** Derive expression for entropy?(5 marks)
**1 (b)** What is lossless compression?(5 marks)
**1 (c)** List attacks threatening security goals.(5 marks)
**1 (d)** Explain the role of digital signature.(5 marks)
**2 (a)** Explain LZW compression algorithm with example.(10 marks)
**2 (b)** For DES symmetric algorithm, explain main steps involved showing block size, cipher key size and round key size.(10 marks)
**3 (a)** For (7, 4) cyclic code, find-out the generator matrix if G(D)=1+D+D^{3}.(10 marks)
**3 (b)** Describe Huffman decoding procedure with example.(10 marks)
**4 (a)** Explain Diffie-Hellman algorithm. Which attack is it valnerable to?(10 marks)
**4 (b)** Describe convolution code in brief.(10 marks)
**5 (a)** State Fermat's Little Theorem with example and its applications.(10 marks)
**5 (b)** Describe lossy compression methods. Where we use lossy compression methods? How do we are it?(10 marks)
**6 (a)** Describe Chinese-Remainder Theorem and its applications.(10 marks)
**6 (b)** Define

i) Hamming distance

ii) Hamming Weight

iii) Syndrome

iv) Linear properties of code

v) Code rate(10 marks)