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SPRING 2016 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
numberof positionsdownthe alphabet. For example, with a left shift of 3, D would be replaced by
A,E wouldbecome B,andso on. The methodisnamedafterJuliusCaesar,who used it in his private
correspondence.
Question. 2. Explain data encryption standard (DES).
Answer:DESworks byusingthe same keyto encryptand decrypta message,so both the sender and
the receivermustknowanduse 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the encryption of electronic data, DES has been superseded by the more secure Advanced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.

2. 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
certainintegerfactorization,discretelogarithm, andellipticcurve relationships.Itiscomputationally
easyfor a userto generate apublicand private key-pairandtouse 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 isamathematical scheme fordemonstrating the authenticity of a digital
message ordocuments.A validdigital signaturegivesarecipientreasontobelieve 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 signaturesare commonlyused 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
basisof 'tickets'to allownodescommunicatingoveranon-secure networktoprove their identity to
one anotherina secure manner.The protocol wasnamedafter the character Kerberos(orCerberus)
from Greek mythology, the ferocious three-headed guard dog of Hades (hellhound). Its designers
aimeditprimarilyata client–servermodelanditprovidesmutual authentication—boththe userand
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,clientauthenticationandencryptedcommunicationbetweenserversandclients.SSL
usesa combinationof public-keyandsymmetric-keyencryptiontosecure aconnectionbetweentwo
machines,typicallya Web or mail server and a client machine, communicating over the Internet or
an internal network.
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