1(a) Encrypt the message "Cryptography is fun" with a multiplicative cipher with key = 15. Decrypt to get back original plaintext.

1(b) With the help of suitable examples compare and contrast mono alphabetic ciphers and poly alphabetic ciphers?

1(c) What are the properties of hash functions? What is the role of a hash function in security?

1(d) What are the different protocols in SSL? How do the client and server establish an SSL connection.

2(a) What is a digital certificate? How does it help to validate the authenticity of a user? Explain the X.509 certificate format.

2(b) With reference to DES comment on the following:

• i) Block size and key size
• ii) Need for expansion permutation
• iii) Avalanche and completeness effects
• iv) Weak keys and semi-weak keys
• v) Role of S-box.

3(a) What are the different types of viruses and worms? How do they propagate?

3(b) What are the various ways for memory and address protection in Operating System?

4(a) Explain briefly with examples, how the following attacks occur:

• i) Phishing attack
• ii) Denial of Service attack
• iii) SQL injection attack
• iv) Cross-site scripting attack

4(b) How is security achieved in the transport and tunnel modes of IPSec? What are security associations?

5(a) What are the different threats to emails? Give an algorithm to secure emails being sent from user A to user B.

5(b) A and B wish to use RSA to communicate securely. A chooses public key as (7,119) and B chooses public key as (13,221). Calculate their private keys.A wishes to send message m=10 to B. What will be the ciphertext? With what key will A encrypt the message "m" if A needs to authenticate itself to B.

6(a) Compare and contrast (any two):

• i) Block and stream ciphers
• ii) MD-5 versus SHA
• iii) Key generation in IDEA and Blowfish

6(b) What are the different components of an Intrusion Detection System? Compare the working of signature based IDS with anomaly based IDS.