Digital Communications

Public Key Cryptosystems

Question 1
Marks : +2 | -2
Pass Ratio : 100%
Which are called the block ciphers?
IDEA
CAST
Triple-DES
All of the mentioned
Explanation:
Some of the examples of block codes are triple-DES, CAST and IDEA.
Question 2
Marks : +2 | -2
Pass Ratio : 100%
In which method, key-stream is generated independently?
Synchronous
Self synchronous
Synchronous & Self synchronous
None of the mentioned
Explanation:
In synchronous encryption system, the key-stream is generated independently of the message.
Question 3
Marks : +2 | -2
Pass Ratio : 100%
For n input bits the number of substitution patterns are
2n
(2n)!
1/2n!
2n!
Explanation:
For n input bits the total number of possible substitution or connection patterns are (2n)!.
Question 4
Marks : +2 | -2
Pass Ratio : 100%
In transposition, the plaintext letters are
Substituted
Rearranged
Removed
None of the mentioned
Explanation:
In permutation or transposition, the positions of the plaintext letters in the message are simply rearranged.
Question 5
Marks : +2 | -2
Pass Ratio : 100%
The substitution of the letters are done
Serially
Parallel way
Serially & Parallel way
None of the mentioned
Explanation:
The substitution part of the encryption scheme is performed in parallel on small segment of the blocks.
Question 6
Marks : +2 | -2
Pass Ratio : 100%
Which algorithm can be used to sign a message?
Public key algorithm
Private key algorithm
Public & Private key algorithm
None of the mentioned
Explanation:
Public key algorithms are used to sign a message and private key algorithms are used to encrypt the messages.
Question 7
Marks : +2 | -2
Pass Ratio : 100%
Private key algorithm is used for _____ encryption and public key algorithm is used for _____ encryption.
Messages, session key
Session key, messages
Can be used for both
None of the mentioned
Explanation:
Private key algorithm is used for encryption of messages and public key algorithm is used for encryption of session keys.
Question 8
Marks : +2 | -2
Pass Ratio : 100%
In a trapdoor function, the functions are easy to go in
One direction
Two directions
All directions
None of the mentioned
Explanation:
A trapdoor is a one way function. Such functions can go easily in only one direction.
Question 9
Marks : +2 | -2
Pass Ratio : 100%
Encryption transformations are known as
Diffusion
Confusion
Diffusion & Confusion
None of the mentioned
Explanation:
The encryption transformations were termed confusion and diffusion by Shannon.
Question 10
Marks : +2 | -2
Pass Ratio : 100%
In cipher feedback method, encryption is done on
Single individual bits
Characters
Single individual bits & Characters
None of the mentioned
Explanation:
In cipher feedback method, single individual bits are encrypted rather than characters and this leads to stream encryption.