5. Cryptography
January-2004 [10]
1.
d) What is a stream cipher? Is DES a stream
or block cipher? [4]
4.
a) What are the
four modes of operation for a symmetric cipher? What are the relative
advantages of each of the mode? [6]
July-2004 [22]
1.
g) Show that in
a block chaining mode of encryption a XOR operation on the decrypted result
with the preceding block produces the plain text. [4]
3.
a) What is steganography? How is it
different from cryptography? [4]
b) Give
expressions describing the triple DES function at the sending and receiving
ends. What is the purpose of the intermediate state? Illustrate how the
intended purpose of the intermediate stage is achieved. [6]
c) Consider the
plain text 47E6BF5193ACD280 and the key FFC16B4A both in
hexadecimal. Apply the following functions on the plain text using the key and
compute the result:
Ri
= Li-1 Å (Ri-1 Å K
i)
Li
= Ri-1 Å (Li-1 Å K
i)
[8]
January-2005 [4]
1.
e) Cryptography
needs physical security. To what extent is this statement correct? [4]
July-2005 [8]
2.
c) Differentiate
between Symmetric Key and Asymmetric Key algorithms? Which is most commonly
used for encryption on the web? [8]
January-2006 [4]
1.
b) Differentiate
between steganography and cryptography. [4]
July-2006 [0]
January-2007 [0]
July-2007 [10]
1.
b) Modern
study of symmetric-key ciphers relates mainly to the study of block ciphers,
stream ciphers and their applications. Explain block ciphers and stream
ciphers. [4]
3.
a) What
is steganography and how it works? What are the advantages and application of
it? [6]
January-2008 [0]
July-2008 [12]
3.
c) What is
steganography and how it works? What are the advantages and application of it? [6]
7.
b) What are the purposes and
functions of a Public Key Infrastructure (PKI) in
cryptography? Explain. [6]
January-2009
[10]
1.
d) Differentiate between
cryptography and steganography. [4]
3.
b) Give
expressions describing the triple DES function at the sending and receiving
ends. What is the purpose of the intermediate stage? Illustrate how the
intended purpose of the intermediate stage is achieved. [6]
July-2009 [14]
1.
b) Cryptanalytic
attacks vary in potency and amount of threat they pose to real-world
cryptosystems. What are the factors on which the practical importance of an
attack depends? [4]
e) What
are the two main branches of public key cryptography? Briefly explain each of
them. [4]
2.
a) In
cryptography, MD5 (Message-Digest algorithm 5) is widely used cryptographic
hash function with a 128-bit hash value. Explain the algorithm. [6]
January-2010 [26]
1.
b) What
is plain text? What is cipher text? Give an example of transformation of plain
text into cipher text? [4]
g) Define
the session key and show how a key distribution centre (KDC) can create a
session key between two users. [4]
3.
a) Describe
the advantages and disadvantages of symmetric and asymmetric key cryptography. [9]
c) The
most powerful and most common approach to secure the points of vulnerabilities
in typical business environment is encryption. If encryption is to be used to
counter the attacks, then there are two alternatives to locate the encryption
function- end to end encryption and link to link encryption. What are the
advantages and disadvantages of both the approaches? [5]
4.
c) How is double DES equivalent to single
DES (Digital Encryption Standard)? [4]
July-2010 [26]
1.
a) How
are block ciphers different from stream ciphers? [4]
d) In a
cryptosystem, P, C and K stand for Plain Text, Cipher text and Key
respectively. Answer the following:
i)
Give an interpretation of the following
equation:
C = Ek2(E
k1(P))
ii)
Give an example of a cryptosystem with the above
property. [4]
2.
b) What
are the various classes of Digital Certificates? List three primary functions
of CERT. [6]
c) How
key distribution can be achieved in symmetric encryption? [6]
7. Write
short notes on any three of the following:
c) Triple
DES [6]
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