Saturday 14 January 2012

network security(6)


6. Public Key Infrastructure &. Message Authentication

January-2004 [16]

1.
f)          What are the three key properties of hash functions?                                                    [4]
4.
b)         ‘A wants to send ‘B’ a signed message. ‘A’ and ‘B’ have certificates for their public keys, signed by a mutually trusted CA. Explain how ‘A’ generates the signature which is appended to the message, assuming RSA, and MD5 can be used.                                 [6]
c)         Does the certification Authority need a private key? What for? What happens if this is compromised?                                                                                                                   [6]

July-2004 [13]

1.
d)         What are session keys? How are they distributed using PKI?                                        [4]
4.
a)         What is hashing? How does it help in checking integrity of a transmitted text?                [4]
b)         Given a message, describe the steps involved in arriving at a digital signature for the message.                                                                                                                [5]

January-2005 [22]

1.
f)          We consider the random cipher model with random variables M, C and K for plaintext, ciphertext and key, respectively. Give an interpretation in cryptographic terms of the equation
                  H(M,C) = H(M)+H(C).                                                                                            [4]
6.
a)         We consider the use of RSA encryption with a 1024 bits modulus to transmit a 56 bit DES key to be used as session key. One can develop a meet-in-the-middle attack on this practice, based on the fact that a random 56 bit number m can with significant probability be factored as m = m1 m2, where both m1 and m2 are 28 bit numbers. So, assume that the DES key m has such a factorization and that the ciphertext c = me mod N has been intercepted by an adversary. Describe the attack in detail and give estimates of how much computation and storage that is needed for the attack.                                           [12]
b)         Nikita and Michael decide to agree on a secret encryption key using the Diffie-Hellman key exchange protocol. You observe the following:
(i)         Nikita chooses p=13 for the modulus and g=2 as generator.
(ii)         Nikita sends 6 to Michael.
(iii)        Michael sends 11 to Nikita.                                                                             [6]

July-2005 [36]

1.
c)         What are the three key properties of hash functions?                                                    [4]
g)         What is non-repudiation? How does Asymmetric key encryption ensure non-repudiation?                                                                                                                                                 [4]
2.
a)         What is a digital signature? Which algorithms are used to digital signatures?                  [4]
6.
a)         How are Digital Certificates used to provide third party trust?                                          [5]
b)         What are the components of X.506 v3 format for digital signatures?                                [6]
c)         What is CRL? How is it used to validate digital certificates?                                           [7]
7.         Write short notes on the following:
a)         Public Key infrastructures (PKI)                                                                                   [6]

January-2006 [32]

1.
a).        What is digital signature? Which algorithms are used for digital signatures?                   [4]
c)         How does message digest help in checking the integrity of a transmitted text?               [4]
2.
a)         Suppose you are doing RSA encryption with the prime numbers p=13 and q=7. Also, assume that encryption exponent e=5. Find the least positive decryption exponent d. Next, encrypt the message m=7. Now decrypt the cipher c=2.                                   [9]
3.
b)         How does RSA based digital signature help in "non-repudiation"? Explain with a concrete example scenario between a sender and a receiver.                                               [6]
c)         Describe the Digital Signature (DS) Algorithm based on DS standard of NIST. How are signing and verifying done in DS standard?                                                                 [9]

July-2006 [22]

1.
d)         What basic arithmetical and logical functions are used in MD5 and SHA-1?                    [4]
4.
a)         Differentiate between both the MD5 and SHA-1 algorithms.                                            [6]
b)         Suppose that A has a data file namely “d” that B needs. A and B want to ensure a secure transmission of file. They do not want that anyone should know the content of file even if it is intercepted during transmission. B also wants to know whether or not whatever is transmitted from A has not been corrupted or altered in transit and that the file was sent by A . It is assumed that A and B share a secret symmetric key that no one else knows and there is a public key infrastructure available.
            Describe the steps that A takes to send the data file “d” meeting the requirements give as above. Your solution should only use as few a number of symmetric and/or public key as necessary while meeting the above requirements.                                                   [12]

January-2007 [20]

3.
a)         In RSA Encryption method if the prime number p and q are 3 and 7 respectively, the encryption exponent e is 11, find the following:
            i)          the least positive decryption exponent d
ii)          public and private key
            iii)         cipher text when the plain text P is encrypted using the public key ?                [10]
5.
a)         Alice sends some message M to Bob using RSA public-Key encryption Algorithm where public key is (5,119) and private key is (77,119). The Cipher text is 66. Find the message M sent to Bob.                                                                                                            [5]
6.
b)         How does Asymmetric key encryption ensure “Non-Repudiation”? Explain with an example?                                                                                                                    [5]

 

July-2007 [22]

1.
c)         A hash function takes a long string (or ‘message’) of any length as input and produces a fixed length string as output, termed a message digest or a digital fingerprint. Briefly explain message authentication code (MAC) in message digest.                                            [4]
4.
c)         Why is MD5 (Message-Digest algorithm 5) widely used in cryptographic hash function with a 128-bit hash value?                                                                                      [6]
6.
a)         How does Asymmetric key encryption ensure “Non-Repudiation”? Explain with an example.                                                                                                                     [6]
7.
d)         RSA involves a public and private key. The public key can be known to everyone and is used for encrypting messages. How are the keys for the RSA algorithm generated? Write steps.                                                                                                                       [6]

January-2008 [40]

1.
f)          What do you understand by authentication? Explain authentication using public key cryptography.                                                                                                           [4]
4.
a)         What are the various classes of Digital certificates? List three primary functions of CERT.                                                                                                                                    [9]
5.
a)         What is encryption? Why is it required? Explain the RSA algorithm of encryption with example.                                                                                                               [9]
b)         What are the major differences between MD4 and MD5?                                   [6]
6.
b)         How does Asymmetric Key Encryption ensures “Non-Repudiation and Privacy”? Explain with an example.                                                                                                [6]
7.
b)         What is CRL? How is it used to validate digital certificates?                                           [6]

July-2008 [28]
1.
e)         A hash function takes a long string (or 'message') of any length as input and produces a fixed length string as output, termed a message digest or a digital fingerprint. Explain message authentication code (MAC) in message digest in brief.                                    [4]

2.
b)         RSA involves a public and private key. How are these keys, for the RSA algorithm, generated? Write steps.          [6]
c)         Explain attack in Diffie-Hellman Key Exchange algorithm.              [6]

3.
b)         In cryptography, MD5 (Message-Digest algorithm 5) is widely used cryptographic hash
function with a 128-bit hash value. Explain the algorithm.                           [6]

5.
c)         How does Assymetric key encryption ensure “Non-Repudiation”? Explain with an
example.           [6]

January-2009 [25]

4.
c)         How does RSA based digital signature help in “non-repudiation”? Explain with a suitable example scenario between a sender and a receiver.    [6]

6.
b)         What are the various classes of Digital certificates? What are the advantages of
International format Standard X.509v3?                 [9]
c)         What is Snooping? Is Diffie-Hellman algorithm susceptible to this attack?               [4]

7.         Write short notes on any three of the following:
a)         Message Digest             [6]

July-2009 [13]

1.
f)          What are the three key properties of hash functions?        [4]

6.
a)         The RSA algorithm involves three steps, key generation, encryption, and decryption. Explain each step.       [9]

January-2010 [7]

1.
f)          Compare the digital signature and conventional signature with respect to the following four parameters: Inclusion, Verification, Relation and Duplicity.          [4]

2.
c)         What are the three broad categories of applications of public key cryptosystems?   [3]

July-2010 [21]

2.
a)         What are the various classes of Digital Certificates? List three primary functions of CERT. [6]

4.
a)         List four public key cryptography algorithms. Explain one of the algorithms where public key cryptosystems is used. [9]

7.         Write short notes on any three of the following:
b)         MD       [6]

No comments:

Post a Comment