BT0088- Cryptography and Network Security

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FALL 2015, ASSIGNMENT

PROGRAM	BSC IT
SEMESTER	FIFTH
SUBJECT CODE & NAME	BT0088- Cryptography and Network Security
CREDITS	4
BK ID	B2069
MARKS	60

Note: Answer all questions. Kindly note that answers for 10 marks questions should be approximately of 400 words. Each question is followed by evaluation scheme.

Question. 1. Explain Caesar’s Cipher encryption technique.

                                                                 

Answer:In cryptography, a Caesar cipher, also known as Caesar's cipher, the shift cipher, Caesar's code or Caesar shift, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. For example, with a left shift of 3, D would be replaced by A, E would become B, and so on. The method is named after Julius Caesar, who used it in his private correspondence.

Question. 2. Explain data encryption standard (DES).

Answer:DES works by using the same key to encrypt and decrypt a message, so both the sender and the receiver must know and use the same private key. Once the go-to, symmetric-key algorithm for the encryption of electronic data, DES has been superseded by the more secure Advanced Encryption Standard (AES) algorithm.

Originally designed by researchers at IBM in the early 1970s, DES was adopted by the U.S. government as an official Federal Information

Question. 3. Describe the principles of Public-Key Cryptosystems.

Answer:Public-key cryptography refers to a set of cryptographic algorithms that are based on mathematical problems that currently admit no efficient solution -- particularly those inherent in certain integer factorization, discrete logarithm, and elliptic curve relationships. It is computationally easy for a user to generate a public and private key-pair and to use it for encryption and decryption. The strength lies in the "impossibility" (computational impracticality) for a properly generated private key to be determined from its corresponding public key. Thus the public key may be published without compromising security. Security depends

Question. 4.Write short notes on

a) Digital signature

Answer:A digital signature is a mathematical scheme for demonstrating the authenticity of a digital message or documents. A valid digital signature gives a recipient reason to believe that the message was created by a known sender, that the sender cannot deny having sent the message (authentication and non-repudiation), and that the message was not altered in transit (integrity). Digital signatures are commonly used for software distribution, financial transactions, and in other cases where it is important to detect forgery or tampering.

Question. 5. Describe Kerberos.

Answer:Kerberos /ˈkərbərəs/ is a computer network authentication protocol which works on the basis of 'tickets' to allow nodes communicating over a non-secure network to prove their identity to one another in a secure manner. The protocol was named after the character Kerberos (or Cerberus) from Greek mythology, the ferocious three-headed guard dog of Hades (hellhound). Its designers aimed it primarily at a client–server model and it provides mutual authentication—both the user and the server verify each other's identity. Kerberos protocol messages are protected against eavesdropping and replay attacks.  Kerberos

Question. 6. Explain Security Socket Layer (SSL).

Answer:The Secure Sockets Layer (SSL) is a computer networking protocol that manages server authentication, client authentication and encrypted communication between servers and clients.SSL uses a combination of public-key and symmetric-key encryption to secure a connection between two machines, typically a Web or mail server and a client machine, communicating over the Internet or an internal network.

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