Digital Communications

Public Key Cryptosystems

Question 1
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 2
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 3
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 4
Marks : +2 | -2
Pass Ratio : 100%
Examples of hash functions are
MD5
SHA-1
MD5 & SHA-1
None of the mentioned
Explanation:
Some examples of hash functions are MD5 and SHA-1.
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%
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 7
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 8
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 9
Marks : +2 | -2
Pass Ratio : 100%
Pretty good privacy program is used for
Electronic mails
File encryption
Electronic mails & File encryption
None of the mentioned
Explanation:
Pretty good privacy (PGP) privacy program is used for both electronic mails and file encryption.
Question 10
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.