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1. Dear students get fully solved assignments
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[ WINTER, 2015 ] ASSIGNMENT
PROGRAM MCA(REVISED FALL 2012)
SEMESTER V
SUBJECT CODE & NAME MCA5042- Cryptography and Network Security
CREDIT 4
BK ID B2069
MAX. MARKS 60
Answer all the Questions
Question.1. Define computer security. Explain the important objectives of computer security.
Answer:Computer security, also known as cybersecurity or IT security, is the protection of
informationsystemsfromtheftordamage tothe hardware,the software,andtothe information on
them,as well asfromdisruptionormisdirectionof the services they provide. It includes controlling
physical access to the hardware, as well as protecting against harm that may come via network
access, data and code injection,and due to malpractice by operators, whether intentional,
accidental, or due to them being tricked into deviating from secure procedures.
The field is of growing importance due to the
Question.2. Explain Feistel Cipher.
Answer:In cryptography, a Feistel cipher is a symmetric structure used in the construction of block
ciphers,namedafterthe German-bornphysicistandcryptographerHorstFeistel whodidpioneering
research while working for IBM (USA); it is also commonly known as a Feistel network. A large
proportion of block ciphers use the scheme, including the Data Encryption Standard (DES). The
Feistel structure hasthe advantage thatencryptionanddecryptionoperationsare verysimilar, even
identical insome cases,requiringonlyareversal of the keyschedule.Therefore the size of the code
or circuitry required to implement such a
Question.3. Explain the following.
(a) Asymmetric Keys
Answer:Anasymmetricalgorithm, asoutlinedinthe Diffie-Hellmanpaper, is a trap door or one-way
function. Sucha functionis easy to perform in one direction, but difficult or impossible to reverse.

2. For example,itiseasytocompute the productof twogivennumbers,butitiscomputationallymuch
harder to find the two factors given only their product. Given both the product and one of the
(b) Public Key Certificate
Answer:Asymmetriccryptographyorpublic-keycryptographyiscryptographyinwhicha pair of keys
isusedto encryptand decrypta message sothat itarrivessecurely.Initially,anetworkuserreceives
a public and private key pair from a certificate authority. Any other user who wants to send an
encrypted
(c) Public Key (Asymmetric) Cryptographic Algorithm
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
easy for a user to
(d) Public Key Infrastructure (PKI)
Answer:A public key infrastructure (PKI) is a set of hardware, software, people, policies, and
procedures needed to create, manage, distribute, use, store, and revoke digital certificates and
manage
Question.4. (a) Explain digital signature.
Answer: A digital signature isamathematical scheme fordemonstratingthe 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.
(b) Explain the different types of attacks on digital signatures.
Answer:In their foundational paper, Goldwasser, Micali, and Rivest lay out a hierarchy of attack
models against digital signatures:
 In a key-only attack, the attacker is only given the public verification key.
 In a known message attack, the attacker is given valid signatures for a variety of messages
known by the attacker but not chosen by the attacker.

3.  In an adaptive chosen
Question.5. Explain the Benefits of IP security.
Answer:Internet Protocol Security (IPSec) is a framework of open standards for ensuring private,
secure communications over Internet Protocol (IP) networks, through the use of cryptographic
securityservices.IPSec is a suite of cryptography-based protection services and security protocols.
Because it requires no changes to programs or protocols, you can easily deploy IPSec for existing
networks.
The driving force for the acceptance and deployment of secure IP is the need for business and
government users to connect their
Question.6. Define the following terms used in the IEEE 802.11 standard.
(a) Access point (AP)
Answer:In computer networking, a wireless access point (WAP) is a networking hardware device
that allowswirelessdevicestoconnecttoa wirednetworkusingWi-Fi, or related standards. The AP
usually connects to a router (via a wired network) as a standalone device, but it can also be an
integral componentof the routeritself.AnAPisdifferentiatedfrom a hotspot, which is the physical
space where
(b) Basic service set (BSS)
Answer: Basic Service Set is a component of the IEEE 802.11 WLAN architecture. This network
architecture isbuiltarounda BasicService Set (BSS), which is actually a set of STAs (the component
that connects to the wireless medium such as a network adapter or NIC) that communicate with
each other. When one access
(c) Coordination function
Answer:Distributed coordination function (DCF) is the fundamental MAC technique of the IEEE
802.11 basedWLAN standard.DCFemploys a CSMA/CA with binary exponential backoff algorithm.
DCF
(d) Distribution system (DS)
Answer:A wirelessdistribution system (WDS) is a system enabling the wireless interconnection of
access pointsinanIEEE 802.11 network.Itallowsawirelessnetworktobe expanded using multiple
access points
(e) Extended service set (ESS)

4. Answer:An extended service set (ESS) is one or more interconnected basic service sets (BSSs) and
their associated
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