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1 Question 1

Using public key cryptography, X adds a digital signature to message M, encrypts < M, >, and sends it to Y, where it is decrypted. Which one of the following sequences of keys is used for the operations?

A

Encryption: X’s private key followed by Y’s private key; Decryption: X’s public

B

Encryption: X’s private key followed by Y’s public key; Decryption: X’s public

C

Encryption: X’s public key followed by Y’s private key; Decryption: Y’s public

D

Encryption: X’s private key followed by Y’s public key; Decryption: Y’s private

key followed by Y’s public key

key followed by Y’s private key

key followed by X’s private key

key followed by X’s public key

GATE CS 2013 Network Security Discuss it

Question 2

In the RSA public key cryptosystem, the private and public keys are (e, n) and (d, n) respectively, where n = p*q and p and q are large primes. Besides, n is public and p and q are private. Let M be an integer such that 0 < M < n and f(n) = (p- 1)(q-1). Now consider the following equations. I. M’= Me mod n M = (M’)d mod n II. ed º 1 mod n III. ed º 1 mod f(n) IV. M’= Me mod f(n) M = (M’)d mod f(n)

Which of the above equations correctly represent RSA cryptosystem?

A

I and II

B

I and III

C

II and IV

D

III and IV

GATE-CS-2009 Network Security Discuss it

Question 3

Which of the following are used to generate a message digest by the network security protocols? (P) RSA (Q) SHA-1 (R) DES (S) MD5

A

P and R only

B

Q and R only

C

Q and S only

D

R and S only

Network Security GATE-CS-2014-(Set-1) Discuss it

Question 4

Suppose that everyone in a group of N people wants to communicate secretly with the N–1 others using symmetric key cryptographic system. The communication between any two persons should not be decodable by the others in the group. The number of keys required in the system as a whole to satisfy the confidentiality requirement is

A

2N

B

N(N – 1)

C

N(N – 1)/2

D

(N – 1)2

Network Security GATE-CS-2015 (Set 1) Discuss it

Question 5

A sender is employing public key cryptography to send a secret message to a receiver. Which one of the following statements is TRUE?

A

Sender encrypts using receiver’s public key

B

Sender encrypts using his own public key

C

Receiver decrypts using sender’s public key

D

Receiver decrypts using his own public key

Network Security GATE-IT-2004 Discuss it

Question 6

Consider that B wants to send a message m that is digitally signed to A. Let the pair of private and public keys for A and B be denoted

represent the operation of encrypting m with a key Kx and H(m) represent the message digest. Which one of the following indicates the CORRECT way of sending the message m along with the digital signature to A?

A

A

B

B

C

C

D

D

Network Security GATE-CS-2016 (Set 1) Discuss it

Question 7

Anarkali digitally signs a message and sends it to Salim. Verification of the signature by Salim requires

A

Anarkali’s public key.

B

Salim’s public key.

2

C

Salim’s private key.

D

Anarkali’s private key.

Network Security GATE-CS-2016 (Set 2) Discuss it

Question 8

Consider the following two statements: i. A hash function (these are often used for computing digital signatures) is an injective function. A. encryption technique such as DES performs a permutation on the elements of its input alphabet. Which one of the following options is valid for the above two statements?

A

Both are false

B

Statement (i) is true and the other is false

C

Statement (ii) is true and the other is false

D

Both are true

Network Security Gate IT 2007 Discuss it

Question 9

The minimum positive integer p such that 3p modulo 17 = 1 is

A

5

B

8

C

12

D

16

Misc Network Security Gate IT 2007 Discuss it

Question 10

Exponentiation is a heavily used operation in public key cryptography. Which of the following options is the tightest upper bound on the number of multiplications required to compute bn mod m,0≤b,n≤m ?

A

O(logn)

B

O(√n)

C

O(n/logn)

D

O(n)

Network Security Gate IT 2007 Discuss it

There are 15 questions to complete. 1 2

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