Digital Communications

Public Key Cryptosystems

Question 1
Marks : +2 | -2
Pass Ratio : 100%
PGP system uses
Private key system
Public key system
Private & Public key system
None of the mentioned
Explanation:
Pretty good privacy system uses both private key and public key based systems.
Question 2
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.
Question 3
Marks : +2 | -2
Pass Ratio : 100%
Public key cryptosystem uses same key for both encryption and decryption.
True
False
Explanation:
Public key cryptosystem uses different keys for encryption and decryption.
Question 4
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 5
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 6
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 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%
In public key cryptosystem _____ keys are used for encryption and decryption.
Same
Different
Encryption Keys
None of the mentioned
Explanation:
In conventional cryptosystem, same keys are used for encryption and decryption where as in public key cryptosystem different keys are used.
Question 10
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.