# RTU Previous Year Question Papers BE CSE 8th Sem

# Information System and Securities May 2011

**UNIT – I**

1 (a) In column A, given are the security services whereas column B. Lists the security mechanisms. Prepare a table showing which mechanism(s) provide each service.

Column A Column B

Peer Entity Authentication Encipherment

Date origin Authentication Digital signatures

Access Control Authentication

Confidentiality Traffic padding

Traffic flow confidentiality Routing control

Data integrity Notarization

Non. repidration Message authentication

Availability File permissions (as in unix)

More than one mechanism may provide the requested service.

(b) List the machanism(s) employed to thwart the following – attacks :

(i) Release of message contents.

(ii) Traffic analysis

(iii) Masquerade

(iv) Replay

(v) Modification of messages

(vi) Denial of service. explain each attack in not more than two sentences each.

(c) Explain the various types of cryptanolytic attacks and arrange these attacks in increasing complexity order.

**OR**

1 (a) In Braytair cipher, the key is “MONARCHY”. Encipher the word “PLAINTEXT BOOK” using the system.

(b) A host connects to an AIM network, sets up a logical connection to another host and is prepared to transfer data to that host. The data is in the form of packets.

(c) The user is to devise a suitable encryption system whether to use link encryption or end-to-end encryption or both. Suggest a suitable encryption scheme and analyze the solution against possible threats.

**UNIT-II**

2 (a) If x_{1?} x_{2} and x_{3} are three consecutive numbers, one of them is divisible by Prove it.

(b) Using the Eucledean algorithm, find (i) gcd (3076, 1776) and

(ii) express gcd as a linear combination of 3076 and 1776.

(c) Prove that no prime of the form 4n+3 can be expressed as sum of two squares.

(d) let a = bmod{m) and c = dmod{m) then (i) a + c = (b + d)mod{m) and (ii) ac = bd mod (m) Prove.

**OR**

(a) Find the reminder when 16^{53} is divided by 7. Use the properties of congruences.

(b) Product of 4 consecutive integers is divisible by 12. Prove it. Find the reminder when 245^{1040} is divided by 18.

(c) Show that Diffie – Heilman key exchange algorithm results in the same key.

**UNIT – III**

3 (a) Explain the terms (i) external error control and (ii) internal error control in messages. Draw neat diagrams to illustrate the two. Also compare the two schemes.

(b) Level of effort for brute force attack on a MAC algorithm is min where k is length of key and n is the length of MAC. Justify the statement.

**OR**

(a) Given below a scheme for distribution of secret key using KDC.

Where E(K,M) repressents encryption of M using K as key. Analyze the above algorithm against replay attack. Suggest, remedy if found to be vulnerable against replay attack.

**UNIT-IV**

(a) In PGP, a user is allowed to home multiple public key/private key pair and can use any pair for communication at any time. Explain the method of communicating to the receiver which pair has been used for encryption. Also

(b) draw general format of a PGP message as sent by a sendor.

What is the role of cerifLcate revocation list in X-509 authentication service ? – Explain.

**OR**

(a) Explain the technical deficiencies in kerberose 4. How these were removed in version 5 ? – Discuss.

(b) What purpose(s) are served by employing X-509. (i) One way

(ii) two-way and (iii) three way authentication procedures. Also draw suitable diagrams for the three procedures with details of messages exchanged.

** **

**UNIT-V**

(a) How IPsec benefits in emproving security of routing applications ? – Discuss.

(b) Explain the procedures used in IPsec for protection against

(i) Replay attack

(ii) Message modification.

Draw suitable digrams.

**OR**

(a)In ISAKMP, cookies are exchanged for prevention against clagging attacks, (b) list the basic requirements required to be satisfied by cookie generation method.

(c) Write short notes on the following :

(i) Handshake protocol (SSL)

(ii) Trusted systems.