Digital Communications

Public Key Cryptosystems

Question 1
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 2
Marks : +2 | -2
Pass Ratio : 100%
Cipher system can be solved effectively by statistically using
Time of occurrence
Frequency of occurrence
Length of the message
None of the mentioned
Explanation:
By statistically using the frequency of occurrence of individual characters and character combinations we can solve many cipher systems.
Question 3
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 4
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 5
Marks : +2 | -2
Pass Ratio : 100%
In stream encryption, the key sequence repeats itself.
True
False
Explanation:
In stream encryption, random key-stream is used. The key sequence never repeats.
Question 6
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 7
Marks : +2 | -2
Pass Ratio : 100%
In public key cryptosystem which is kept as public?
Encryption keys
Decryption keys
Encryption & Decryption keys
None of the mentioned
Explanation:
In public key cryptosystem, the encryption keys are kept as public where as decryption keys are kept as secret.
Question 8
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 9
Marks : +2 | -2
Pass Ratio : 100%
Which has a key length of 128 bits?
IDEA
Triple-DES
IDEA & Triple-DES
None of the mentioned
Explanation:
Triple-DES uses 168 bit key size and IDEA and CAST uses 128 bits key length.
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.