This set of Digital Communications Multiple Choice Questions & Answers (MCQs) focuses on “Public key cryptosystem – 1”.
1. In public key cryptosystem _____ keys are used for encryption and decryption.
a) Same
b) Different
c) Encryption Keys
d) None of the mentioned
View Answer
Explanation: In conventional cryptosystem, same keys are used for encryption and decryption where as in public key cryptosystem different keys are used.
2. In public key cryptosystem which is kept as public?
a) Encryption keys
b) Decryption keys
c) Encryption & Decryption keys
d) None of the mentioned
View Answer
Explanation: In public key cryptosystem, the encryption keys are kept as public where as decryption keys are kept as secret.
3. In a trapdoor function, the functions are easy to go in
a) One direction
b) Two directions
c) All directions
d) None of the mentioned
View Answer
Explanation: A trapdoor is a one way function. Such functions can go easily in only one direction.
4. Pretty good privacy program is used for
a) Electronic mails
b) File encryption
c) Electronic mails & File encryption
d) None of the mentioned
View Answer
Explanation: Pretty good privacy (PGP) privacy program is used for both electronic mails and file encryption.
5. PGP system uses
a) Private key system
b) Public key system
c) Private & Public key system
d) None of the mentioned
View Answer
Explanation: Pretty good privacy system uses both private key and public key based systems.
6. Private key algorithm is used for _____ encryption and public key algorithm is used for _____ encryption.
a) Messages, session key
b) Session key, messages
c) Can be used for both
d) None of the mentioned
View Answer
Explanation: Private key algorithm is used for encryption of messages and public key algorithm is used for encryption of session keys.
7. Which are called the block ciphers?
a) IDEA
b) CAST
c) Triple-DES
d) All of the mentioned
View Answer
Explanation: Some of the examples of block codes are triple-DES, CAST and IDEA.
8. Which has a key length of 128 bits?
a) IDEA
b) Triple-DES
c) IDEA & Triple-DES
d) None of the mentioned
View Answer
Explanation: Triple-DES uses 168 bit key size and IDEA and CAST uses 128 bits key length.
9. Which algorithm can be used to sign a message?
a) Public key algorithm
b) Private key algorithm
c) Public & Private key algorithm
d) None of the mentioned
View Answer
Explanation: Public key algorithms are used to sign a message and private key algorithms are used to encrypt the messages.
10. Examples of hash functions are
a) MD5
b) SHA-1
c) MD5 & SHA-1
d) None of the mentioned
View Answer
Explanation: Some examples of hash functions are MD5 and SHA-1.
11. A cryptographic hash function has variable output length.
a) True
b) False
View Answer
Explanation: A cryptographic hash function has fixed output length.
12. A set of numbers is called as super increasing if
a) Each element is greater than previous element
b) Each element greater than sum of all the previous elements
c) Each element greater than the average of all elements
d) Each element lesser than the sum of all the elements
View Answer
Explanation: A set of numbers is called as super increasing if each element is greater than the sum of all the numbers lesser than it.
13. Knapsack problem can be solved by
a) Public key cryptosystem
b) Private key cryptosystem
c) Public & Private key cryptosystem
d) None of the mentioned
View Answer
Explanation: The knapsack problem can be solved by public key cryptosystem system using knapsack vector and data vector.
14. Merkle hellman is a symmetric cryptosystem.
a) True
b) False
View Answer
Explanation: Merkell hellman cryptosystem is a public key asymmetric cryptosystem method.
15. In this Merkle Hellman method same key is used for encryption and decryption.
a) True
b) False
View Answer
Explanation: In Merkle hellman cryptosystem method, two separate private and public keys are used for encryption and decryption.
Sanfoundry Global Education & Learning Series – Digital Communications.
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