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- Cryptography And Network Security - CNS
- 2018
- PYQ
**Biju Patnaik University of Technology BPUT - BPUT**- Electronics and Communication Engineering
- B.Tech
**3971 Views**- 97 Offline Downloads
- Uploaded 11 months ago

Registration No : Total Number of Pages : 02 B.Tech. FECE6404 8th Semester Regular / Back Examination 2017-18 NETWORK SECURITY AND CRYPTOGRAPHY BRANCH: AEIE, ECE, EIE, ETC, IEE Time : 3 Hours Max Marks : 70 Q.CODE : C465 Answer Question No.1 which is compulsory and any FIVE from the rest. The figures in the right hand margin indicate marks. Answer all parts of a question at a place. Q1. a) b) c) d) e) f) g) h) i) j) Q2. a) b) Q3. a) b) Answer the following questions : Short answer type : Define the three security goals. Find all multiplicative inverses in Z10. Define linear congruence. Use the additive cipher with key = 15 to decrypt the message “WTAAD”. Are all stream ciphers monoalphabetic? Justify your answer. Briefly describes MixColumns. What is a one-way function? Is it necessary to recover the secret key in order to attack a MAC algorithm? Define virus. Specify the different types of viruses. List the design goals of firewalls. (2 x 10) In each of the following ciphers, what is the maximum number of characters that will be changed in the ciphertext if only a single character is changed in the plaintext? (i) Additive (ii) Multiplicative (iii) Affine (iv) Rotor (v) Enigma. Use the Vigenere cipher with keyword “HEALTH” to encipher the message “Life is full of surprises”. (5) Find the result of (x5 + x2 + x) ʘ (x7 + x4 + x3 + x2 + x) in GF(28) with irreducible polynomial (x8 + x4 + x3 + x + 1). Note that symbol ʘ is used to show the multiplication of two polynomials. Find all integers x which leave a remainder of 1, 2, 3 and 4 when divided by 5, 7, 9 and 11 respectively. (5) (5) (5) Q4. a) b) Show that DES decryption is in fact the inverse of DES encryption. State Fermat’s little theorem and explain its use by giving one example. (5) (5) Q5. a) (5) b) Perform encryption and decryption using the RSA algorithm for the following: (i) p = 3, q = 11, e = 7 and M = 5 (ii) p = 5, q = 11, e = 3 and M = 9 Explain various ethical issues in computer security. a) b) Compare the features of SHA-1 and MD5 algorithm. Explain the architecture of IP security. (5) (5) Q6. (5)

Q7. Explain Diffie-Hellman key exchange algorithm. Users A and B use this algorithm with a common prime q = 71 and a primitive root α = 7. (i) If user A has private key XA = 5, what is A’s public key YA? (ii) If user B has private key XB = 12, what is B’s public key YB? (iii) What is the shared secret key? Q8. a) b) c) d) Write short answer on any TWO : Transport Layer Security Intrusion Detection System Elliptic Curve Cryptosystem Primality Testing Methods (10) (5 x 2)

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